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Sökning: AMNE:(TEKNIK OCH TEKNOLOGIER) AMNE:(Materialteknik) AMNE:(Keramteknik)

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1.
  • Buckland, Philip I., 1973-, et al. (författare)
  • The Strategic Environmental Archaeology Database : a resource for international, multiproxy and transdisciplinary studies of environmental and climatic change
  • 2015
  • Konferensbidrag (refereegranskat)abstract
    • Climate and environmental change are global challenges which require global data and infrastructure to investigate. These challenges also require a multi-proxy approach, integrating evidence from Quaternary science and archaeology with information from studies on modern ecology and physical processes among other disciplines. The Strategic Environmental Archaeology Database (SEAD http://www.sead.se) is a Swedish based international research e-infrastructure for storing, managing, analysing and disseminating palaeoenvironmental data from an almost unlimited number of analysis methods. The system currently makes available raw data from over 1500 sites (>5300 datasets) and the analysis of Quaternary fossil insects, plant macrofossils, pollen, geochemistry and sediment physical properties, dendrochronology and wood anatomy, ceramic geochemistry and bones, along with numerous dating methods. This capacity will be expanded in the near future to include isotopes, multi-spectral and archaeo-metalurgical data. SEAD also includes expandable climate and environment calibration datasets, a complete bibliography and extensive metadata and services for linking these data to other resources. All data is available as Open Access through http://qsead.sead.se and downloadable software. SEAD is maintained and managed at the Environmental Archaeology Lab and HUMlab at Umea University, Sweden. Development and data ingestion is progressing in cooperation with The Laboratory for Ceramic Research and the National Laboratory for Wood Anatomy and Dendrochronology at Lund University, Sweden, the Archaeological Research Laboratory, Stockholm University, the Geoarchaeological Laboratory, Swedish National Historical Museums Agency and several international partners and research projects. Current plans include expanding its capacity to serve as a data source for any system and integration with the Swedish National Heritage Board's information systems. SEAD is partnered with the Neotoma palaeoecology database (http://www.neotomadb.org) and a new initiative for building cyberinfrastructure for transdisciplinary research and visualization of the long-term human ecodynamics of the North Atlantic funded by the National Science Foundation (NSF).
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2.
  • Mahade, Satyapal, 1987-, et al. (författare)
  • Incorporation of graphene nano platelets in suspension plasma sprayed alumina coatings for improved tribological properties
  • 2021
  • Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 570
  • Tidskriftsartikel (refereegranskat)abstract
    • Graphene possesses high fracture toughness and excellent lubrication properties, which can be exploited to enhance tribological performance of coating systems utilized to combat wear. In this work, suspension plasma spray (SPS) process was employed to deposit a composite, graphene nano-platelets (GNP) incorporated alumina coating. For comparison, monolithic alumina was also deposited utilizing identical spray conditions. The as-deposited coatings were characterized in detail for their microstructure, porosity content, hardness, fracture toughness and phase composition. Raman analysis of the as-deposited composite coating confirmed retention of GNP. The composite coating also showed good microstructural integrity, comparable porosity, higher fracture toughness and similar alumina phase composition as the monolithic alumina coating. The as-deposited coatings were subjected to dry sliding wear tests. The GNP incorporated composite coating showed lower CoF and lower specific wear rate than the pure alumina coating. Additionally, the counter surface also showed a lower wear rate in case of the composite coating. Post-wear analysis performed by SEM/EDS showed differences in the coating wear track and in the ball wear track of monolithic and composite coatings. Furthermore, Raman analysis in the wear track of composite coating confirmed the presence of GNP. The micro-indentation and wear test results indicate that the presence of GNP in the composite coating aided in improving fracture toughness, lowering CoF and specific wear rate compared to the monolithic coating. Results from this work demonstrated retention of GNP in an SPS processed coating, which can be further exploited to design superior wear-resistant coatings.
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3.
  • Grolig, Jan Gustav, 1986 (författare)
  • Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells - Material Development and Electrical Properties
  • 2015
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Solid oxide fuel cells (SOFCs) are attracting increasing interest as devices with potentialuses in decentralized and clean electricity and heat production. Several challengeswith respect to materials have to be overcome to achieve efficiencies and life-spansthat are sufficient for long-term applications.An important element of an SOFC stack is the interconnect component, which connectstwo adjacent fuel cell elements. Interconnects, which are commonly composedof ferritic stainless steels, have to be corrosion-resistant, mechanically stable and costoptimized.This work aimed to investigate economic solutions for interconnect materials and tounderstand the underlying mechanisms of degradation and electrical conduction ofthese materials. Mainly two substrates, a commercially available steel (AISI 441) anda ferritic stainless steel that was optimized for an SOFC application (Sandvik SanergyHT) were combined with different barrier coatings and exposed to a cathode-sideatmosphere. A method was developed that allows for the electrical characterizationof promising material systems and model alloys, thereby facilitating a fundamentalunderstanding of the dominant electrical conduction processes linked to the oxidescales that grow on interconnects. The AISI 441 steel coated with reactive elementsand cobalt showed good corrosion and chromium evaporation profiles, while AISI 441coated with cerium and cobalt also had promising electrical properties. The SanergyHT steel was examined with coatings of copper and iron and copper and manganese,respectively. The corrosion and chromium evaporation profiles of Sanergy HT wereimproved by coating with copper and iron. The copper and iron-coated Sanergy HTshowed lower area specific resistance values than cobalt-coated Sanergy HT. Chromia,which is the main constituent of oxide scales, was synthesized using differentmethods. The electrical properties of chromia were found to be sensitive to not onlyimpurities, but also heat treatment. Finally the electrical properties of cobalt- andcobalt cerium-coated Sanergy HT steels were investigated. It was revealed that theaddition of cerium improved the conductivity of the interconnect by both slowingdown chromia growth and preventing the outward diffusion of iron into the spinel.
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4.
  • Krakhmalev, Pavel, 1973-, et al. (författare)
  • Microstructure, solidification texture, and thermal stability of 316 L stainless steel manufactured by laser powder bed fusion
  • 2018
  • Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 8:8, s. 1-18
  • Tidskriftsartikel (refereegranskat)abstract
    • This article overviews the scientific results of the microstructural features observed in 316 L stainless steel manufactured by the laser powder bed fusion (LPBF) method obtained by the authors, and discusses the results with respect to the recently published literature. Microscopic features of the LPBF microstructure, i.e., epitaxial nucleation, cellular structure, microsegregation, porosity, competitive colony growth, and solidification texture, were experimentally studied by scanning and transmission electron microscopy, diffraction methods, and atom probe tomography. The influence of laser power and laser scanning speed on the microstructure was discussed in the perspective of governing the microstructure by controlling the process parameters. It was shown that the three-dimensional (3D) zig-zag solidification texture observed in the LPBF 316 L was related to the laser scanning strategy. The thermal stability of the microstructure was investigated under isothermal annealing conditions. It was shown that the cells formed at solidification started to disappear at about 800 °C, and that this process leads to a substantial decrease in hardness. Colony boundaries, nevertheless, were quite stable, and no significant grain growth was observed after heat treatment at 1050 °C. The observed experimental results are discussed with respect to the fundamental knowledge of the solidification processes, and compared with the existing literature data.
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5.
  • Zhang, Hanzhu, 1991-, et al. (författare)
  • A high-entropy B4(HfMo2TaTi)C and SiC ceramic composite
  • 2019
  • Ingår i: Dalton Transactions. - : Royal Society of Medicine Press. - 1477-9226 .- 1477-9234. ; 48:16, s. 5161-5167
  • Tidskriftsartikel (refereegranskat)abstract
    • A multicomponent composite of refractory carbides, B4C, HfC, Mo2C, TaC, TiC and SiC, of rhombohedral, face-centered cubic (FCC) and hexagonal crystal structures is reported to form a single phase B4(HfMo2TaTi)C ceramic with SiC. The independent diffusion of the metal and nonmetal atoms led to a unique hexagonal lattice structure of the B4(HfMo2TaTi)C ceramic with alternating layers of metal atoms and C/B atoms. In addition, the classical differences in the crystal structures and lattice parameters among the utilized carbides were overcome. Electron microscopy, X-ray diffraction and calculations using density functional theory (DFT) confirmed the formation of a single phase B4(HfMo2TaTi)C ceramic with a hexagonal close-packed (HCP) crystal structure. The DFT based crystal structure prediction suggests that the metal atoms of Hf, Mo, Ta and Ti are distributed on the (0001) plane in the HCP lattice, while the carbon/boron atoms form hexagonal 2D grids on the (0002) plane in the HCP unit cell. The nanoindentation of the high-entropy phase showed hardness values of 35 GPa compared to the theoretical hardness value estimated based on the rule of mixtures (23 GPa). The higher hardness was contributed by the solid solution strengthening effect in the multicomponent hexagonal structure. The addition of SiC as the secondary phase in the sintered material tailored the microstructure of the composite and offered oxidation resistance to the high-entropy ceramic composite at high temperatures.
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6.
  • Xu, Jinghao, et al. (författare)
  • Short-term creep behavior of an additive manufactured non-weldable Nickel-base superalloy evaluated by slow strain rate testing
  • 2019
  • Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 179, s. 142-157
  • Tidskriftsartikel (refereegranskat)abstract
    • Additive manufacturing (AM) of high γ′ strengthened Nickel-base superalloys, such as IN738LC, is of high interest for applications in hot section components for gas turbines. The creep property acts as the critical indicator of component performance under load at elevated temperature. However, it has been widely suggested that the suitable service condition of AM processed IN738LC is not yet fully clear. In order to evaluate the short-term creep behavior, slow strain rate tensile (SSRT) tests were performed. IN738LC bars were built by laser powder-bed-fusion (L-PBF) and then subjected to hot isostatic pressing (HIP) followed by the standard two-step heat treatment. The samples were subjected to SSRT testing at 850 °C under strain rates of 1 × 10−5/s, 1 × 10−6/s, and 1 × 10−7/s. In this research, the underlying creep deformation mechanism of AM processed IN738LC is investigated using the serial sectioning technique, electron backscatter diffraction (EBSD), transmission electron microscopy (TEM). On the creep mechanism of AM polycrystalline IN738LC, grain boundary sliding is predominant. However, due to the interlock feature of grain boundaries in AM processed IN738LC, the grain structure retains its integrity after deformation. The dislocation motion acts as the major accommodation process of grain boundary sliding. Dislocations bypass the γ′ precipitates by Orowan looping and wavy slip. The rearrangement of screw dislocations is responsible for the formation of subgrains within the grain interior. This research elucidates the short-creep behavior of AM processed IN738LC. It also shed new light on the creep deformation mechanism of additive manufactured γ′ strengthened polycrystalline Nickel-base superalloys.
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7.
  • Zhang, Hanzhu, 1991-, et al. (författare)
  • Refractory multicomponent boron-carbide high entropy oxidation-protective coating for carbon-carbon composites
  • 2021
  • Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 425
  • Tidskriftsartikel (refereegranskat)abstract
    • A novel refractory multicomponent boron-carbide coating of 300 nm thickness, HfMoTaTi-BC, was deposited on carbon-carbon composites (CCC). The coating showed a face-centred cubic (FCC) structure of lattice parameter of 0.4429 nm with an average crystallite size of 5 nm. The FCC coating transformed from single-phase solid solution into multiple ceramic carbides and boride phases at 900°C during long-term thermal stability test. The exposure of HEC coated CCC to the flame (2000°C) of liquefied petroleum gas (LPG) torch for 5 minutes revealed that the film had excellent resistance to oxidation and protected the CCC material under extreme aerothermal heating.
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8.
  • Hanning, Fabian, et al. (författare)
  • The Effect of Grain Size on theSusceptibility Towards Strain Age Crackingof Wrought Haynes® 282®
  • 2020
  • Ingår i: SPS 2020. - Amsterdam : IOS Press. - 9781643681467 - 9781643681474 ; 13, s. 407-416
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • The effect of grain size on the suceptibility towards strain age cracking (SAC) has been investigated for Haynes® 282® in the tempeature range of 750 to 950°C after isothermal exposure up to 1800s. Grain growth was induced by heattreating the material at 1150°C for 2h, resulting in a fourfold increase in grain size. Hardness was significanlty reduced after heat treatment as compared to millannealed material. Large grain size resulted in intergranular fracture over a widertemperature range than small grain size material. Ductility was lowest at 850°C, while lower values were observed to be correlated to increased grain size. The rapid formation of grain boundary carbide networks in Haynes® 282® is found to be notable to compensate for higher local stresses on grain boundaries due to incresedgrain size. 
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9.
  • Qin, Xiao, 1993, et al. (författare)
  • Microstructure and texture evolutions in FeCrAl cladding tube during pilger processing
  • 2023
  • Ingår i: Journal of Materials Research and Technology. - 2238-7854. ; 25, s. 5506-5519
  • Tidskriftsartikel (refereegranskat)abstract
    • The microstructure of FeCrAl cladding tubes depends on the fabricating process history. In this study, the microstructural characteristics of wrought FeCrAl alloys during industrial pilger processing into thin-walled tubes were investigated. The hot extruded tube showed ∼100 μm equiaxed grains with weak α∗-fiber in {h11}<1/h12> texture, while pilger rolling process change the microstructure to fragmented and elongated grains along the rolling direction. The pilgered textures could be predicted with the VPSC model. The inter-pass annealing at 800–850 °C for 1 h results in recovery and recrystallization of the ferric matrix and restoration of ductility. The final finished tube shows fine recrystallized grains (∼11 μm) with dominant γ-fiber in three dimensions. Pilger rolling enhanced α-fiber while annealing reduced α-fiber and enhanced γ-fiber. Microstructural evolution in the Laves precipitates followed the sequence of faceted needle-like → spherical → faceted ellipsoidal. Thermomechanical processing resulted in cladding tubes with an area fraction of ∼5% and a number density of 5 × 10−11 m−2 in Laves precipitates, which is half that of the first-pilgered tube. Laves precipitates pin the grain boundaries to control the microstructure and prevent grain coarsening.
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10.
  • Shoja, Siamak, 1980 (författare)
  • Microstructure and plastic deformation of textured CVD alumina coatings
  • 2020
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • It is known that the wear performance of α-alumina coatings produced by chemical vapor deposition (CVD) is significantly influenced by the type and degree of texture. However, the main reasons behind this behavior are not fully understood. This thesis contains studies of two related topics for increasing the understanding of α-alumina coatings. The first topic concerns the microstructure and texture development of CVD α-Al2O3 coatings, and the second topic concerns calculations and analysis of the Schmid factors ( m ) for coatings with different textures. By combining different analysis methods (such as XRD, SEM, FIB/SEM, TKD, TEM, STEM, XEDS), and theoretical and experimental Schmid factor analysis by MATLAB and EBSD, the microstructure and plastic deformation of α-alumina coatings were investigated.     The microstructures of three different CVD α-Al2O3 layers deposited onto a Ti(C,N,O) bonding layer were studied. Grain boundary diffusion of heavy elements from the substrate to the bonding layer/α-Al2O3 interface was observed. This may be the cause of a disturbance in the early growth of α-Al2O3. Additionally, it was found that the number of interfacial pores at the bonding layer/α-Al2O3 interface increased by introducing the H2S gas. The H2S gas also promoted an earlier development of the (0001) texture. The orientation of the grains was developed to the desired texture both as a gradual change over several grains and as an abrupt transformation from one grain to another.   The probability of plastic deformation in different wear zones on the rake face of a cutting tool was investigated theoretically and experimentally by analyzing Schmid factors for textured α-Al2O3 coatings. Schmid factor diagrams were constructed using MATLAB/MTEX and used to extract frequency distributions for different slip systems and textures. The results were compared with lateral distribution maps of Schmid factors obtained from experimental coatings. It was observed that basal slip is most easily activated in the transition zone, followed by prismatic slip systems 1 and 2 in coatings with an (0001)-texture. The homogeneous plastic deformation behavior observed in this coating is also connected to mostly high Schmid factors in the  m -value distribution. The differences between the  m -value distributions for the three slip systems are not that pronounced in the (01-1​2) and (11-20) textures, and the distributions are relatively wide. The low wear rate and more homogeneous deformation of the coating with (0001) texture compared to the other coating textures may be the result of the high plasticity, offered by the easy activation of basal slip and prismatic 1 slip, and the low spread of Schmid factor values at the transition zone.   In conclusion, the results presented in this thesis form a knowledge platform that can be used to understand the microstructure and wear mechanisms of textured CVD α-alumina coatings.
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11.
  • Saarimäki, Jonas, et al. (författare)
  • 3D Residual Stresses in Selective Laser Melted Hastelloy X
  • 2017
  • Ingår i: Residual Stresses 2016: ICRS-10, Materials Research Proceedings 2 (2016). - : Materials Research Forum LLC. ; , s. 73-78
  • Konferensbidrag (refereegranskat)abstract
    • 3D residual stresses in as manufactured EOS NickelAlloy HX, produced by laser powder bed additive manufacturing, are analysed on the surface closest to the build-plate. Due to the severe thermal gradient produced during the melting and solidification process, profound amounts of thermal strains are generated. Which can result in unwanted geometrical distortion and effect the mechanical properties of the manufactured component. Measurements were performed using a four-circle goniometer Seifert X-ray machine, equipped with a linear sensitive detector and a Cr-tube. Evaluation of the residual stresses was conducted using sin2ψ method of the Ni {220} diffraction peak, together with material removal technique to obtain in-depth profiles. An analysis of the material is reported. The analysis reveals unwanted residual stresses, and a complicated non-uniform grain structure containing large grains with multiple low angle grain boundaries together with nano-sized grains. Grains are to a large extent, not equiaxed, but rather elongated.
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12.
  • Ciurans Oset, Marina, 1993-, et al. (författare)
  • Processing of Macroporous Alumina Ceramics Using Pre-Expanded Polymer Microspheres as Sacrificial Template
  • 2018
  • Ingår i: Ceramics. - : MDPI. - 2571-6131. ; 1:2, s. 329-342
  • Tidskriftsartikel (refereegranskat)abstract
    • Shaped porous ceramics have proven to be the most adapted materials for several industrial applications, both at low and high temperatures. Recent research has been focused on developing shaping techniques, allowing for a better control over the total porosity and the pores characteristics. In this study, macroporous alumina foams were fabricated by gel-casting using pre-expanded polymeric microspheres with average sizes of 40 μm, 20 μm, and 12 μm as sacrificial templates. The gel-casting method, as well as the drying, debinding, and presintering conditions were investigated and optimized to process mechanically strong and highly porous alumina scaffolds. Furthermore, a reliable model relating the amount of pre-expanded polymeric microspheres and the total porosity of the presintered foams was developed and validated by mercury intrusion porosimetry measurements. The electron microscopy investigation of the presintered foams revealed that the size distribution and the shape of the pores could be tailored by controlling the particle size distribution and the shape of the wet pre-expanded microspheres. Highly uniform and mechanically stable alumina foams with bimodal porosity ranging from 65.7 to 80.2 vol. % were processed, achieving compressive strengths from 3.3 MPa to 43.6 MPa. Given the relatively open pore structure, the pore size distribution, the presintered mechanical strength, and the high porosity achieved, the produced alumina foams could potentially be used as support structures for separation, catalytic, and filtration applications.
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13.
  • Jiang, Zhiwu, et al. (författare)
  • Combustion synthesis and mechanical properties of MoSi2­-ZrB2­-SiC ceramics
  • 2018
  • Ingår i: Journal of the Ceramic Society of Japan. - : Ceramic Society of Japan. - 1882-0743 .- 1348-6535. ; 126:7, s. 504-509
  • Tidskriftsartikel (refereegranskat)abstract
    • MoSi2ZrB2SiC ceramics were synthesized using Mo, Zr, Si and B4C powders by self-propagating high-temperature synthesis and densifying by spark plasma sintering. The effects of MoSi2 content on the combustion synthesis process, microstructure, and mechanical properties of the ceramics were investigated. The results showed that combustion synthesis is an unstable mode, spiral combustion. The Gibbs calculations and combustion temperature curves indicate there are two reactions occurring at the same time. The volume fraction of the four different phases and their relative densities were also measured and calculated. Compared to pure MoSi2, the 1.0MoSi20.2ZrB20.1SiC (M10) ceramic exhibits excellent mechanical properties with its maximum Vickers hardness and fracture toughness being 14.0 GPa and of 5.5 MPa m1/2, respectively. The hardness is in agreement with the rule of mixture. The morphology of indentation cracks reveals that the fracture toughness improves as a result of toughening mechanisms such as crack bridge, crack deflection, and microcracks.
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14.
  • Mangalaraja, R.V., et al. (författare)
  • Microwave assisted combustion synthesis of nanocrystalline yttria and its powder characteristics
  • 2009
  • Ingår i: Powder Technology. - : Elsevier BV. - 0032-5910 .- 1873-328X. ; 191:3, s. 309-314
  • Tidskriftsartikel (refereegranskat)abstract
    • Microwave assisted combustion synthesis is used for fast and controlled processing of advanced ceramics. Single phase and sinter active nanocrystalline cubic yttria powders were successfully synthesized by microwave assisted combustion using the organic fuels urea, citric acid and glycine as reducing agents. The precursor powders were investigated by thermogravimetry (TG) and differential scanning colorimetry (DSC) analyses. The as-prepared precursors and the resulting oxide powders calcined at 1100 °C in oxygen atmosphere were characterized for their structure, particle size and morphology. The thermal analyses (TG/DSC), X-ray diffraction (XRD) and Fourier transform infra red (FT-IR) results demonstrate the effectiveness of the microwave assisted combustion synthesis. The scanning electron microscopy (SEM) observations show the different morphologies of as-prepared powders and transmission electron microscopy (TEM) shows the particle sizes in the range of 30-100 nm for calcined powders for different fuels. The results confirm that the homogeneous, nano scale yttria powders derived by microwave assisted combustion have high crystalline quality and the morphology of the as-prepared precursor powders depends on the nature of organic fuel used.
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15.
  • Procter, Philip, et al. (författare)
  • Designing A Commercial Biomaterial For A Specific Unmet Clinical Need – : An Adhesive Odyssey
  • 2018
  • Konferensbidrag (refereegranskat)abstract
    • There are clinical situations in fracture repair, e.g. osteochondral fragments, where current implant hardware is insufficient. The proposition of an adhesive enabling fixation and healing has been considered but no successful candidate has emerged thus far. The many preclinical and few clinical attempts include fibrin glue, mussel adhesive and even “Kryptonite” (US bone void filler). The most promising recent attempts are based on phosphorylating amino acids, part of a common cellular adhesion mechanism linking mussels, caddis fly larvae, and mammals. Rapid high bond strength development in the wetted fatty environment of fractured bone, that is sustained during biological healing, is challenging to prove both safety and efficacy. Additionally, there are no “predicate” preclinical animal and human models which led the authors to develop novel evaluations for an adhesive candidate “OsStictm” based on calcium salts and amino acids. Adhesive formulations were evaluated in both soft (6/12 weeks) and hard tissue (3,7,10,14 & 42 days) safety studies in murine models. The feasibility of a novel adhesiveness test, initially proven in murine cadaver femoral bone, is being assessed in-vivo (3,7,10,14 & 42 days) in bilateral implantations with a standard tissue glue as the control. In parallel an ex-vivo human bone model using freshly harvested human donor bone is under development to underwrite the eventual clinical application of such an adhesive. This is part of a risk mitigation project bridging between laboratory biomaterial characterisation and a commercial biomaterial development where safety and effectiveness have to meet today´s new medical device requirements.
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16.
  • Pujari-Palmer, Michael, et al. (författare)
  • A Novel Class of Injectable Bioceramics That Glue Tissues and Biomaterials
  • 2018
  • Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 11:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Calcium phosphate cements (CPCs) are clinically effective void fillers that are capable of bridging calcified tissue defects and facilitating regeneration. However, CPCs are completely synthetic/inorganic, unlike the calcium phosphate that is found in calcified tissues, and they lack an architectural organization, controlled assembly mechanisms, and have moderate biomechanical strength, which limits their clinical effectiveness. Herein, we describe a new class of bioinspired CPCs that can glue tissues together and bond tissues to metallic and polymeric biomaterials. Surprisingly, alpha tricalcium phosphate cements that are modified with simple phosphorylated amino acid monomers of phosphoserine (PM-CPCs) bond tissues up to 40-fold stronger (2.5-4 MPa) than commercial cyanoacrylates (0.1 MPa), and 100-fold stronger than surgical fibrin glue (0.04 MPa), when cured in wet-field conditions. In addition to adhesion, phosphoserine creates other novel properties in bioceramics, including a nanoscale organic/inorganic composite microstructure, and templating of nanoscale amorphous calcium phosphate nucleation. PM-CPCs are made of the biocompatible precursors calcium, phosphate, and amino acid, and these represent the first amorphous nano-ceramic composites that are stable in liquids.
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17.
  • da Silva, Melina, 1978, et al. (författare)
  • A comparison of thermal stability in nanocrystalline Ni- and Co-based materials
  • 2005
  • Ingår i: International Journal of Materials Research. - : Walter de Gruyter GmbH. - 1862-5282 .- 2195-8556. ; 96:09, s. 1009-1014
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper the microstructural development upon annealing of nanocrystalline Ni- and Co-based electrodeposits is described. New investigations on Ni, Ni - Fe, and Co-P are compared with previous results on Ni, Co, and Ni -P in terms of microstructural changes and stabilizing mechanisms. The conclusions are: pure nanocrystalline Ni and Co are stabilized by impurities in the grain boundaries. In the case of Co, also an allotropic phase transformation influences the occurrence of abnormal grain growth. Alloying and/or adding solutes is found to increase thermal stability. While in Ni-20 at.% Fe the ordering transformation is expected to be the reason for stabilization, in strongly segregating systems (Ni -P and Co-P) the stabilizing effect is the decrease in grain boundary energy due to solute segregation. After precipitation, Zener pinning still hinders grain boundary migration, but not sufficient to stabilize the nanocrystalline structure.
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18.
  • Löffler, Markus, 1980, et al. (författare)
  • Adhesion layer-bottom electrode interaction during BaxSr1−xTiO3 growth as a limiting factor for device performance
  • 2012
  • Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 111:12, s. Art. no. 124514-
  • Tidskriftsartikel (refereegranskat)abstract
    • Changes in bottom electrode morphology and adhesion layer composition upon deposition of BaxSr1-xTiO3 (BSTO) at elevated temperatures have been found, which have a negative impact on acoustic wave resonator device performance. The difference between nominal and actual adhesion layer composition are explained by grain boundary diffusion of Ti or W and their oxidation by in-diffusing oxygen, which leads to an increased interface roughness between the Pt bottom electrode and the BSTO. It is shown, that room-temperature deposited TiO2 diffusion barriers fail to protect against Ti oxidation and diffusion. Also W adhesion layers are prone to this phenomenon, which limits their ability to act as high temperature resistant adhesion layers for bottom electrodes for ferroelectric thin films.
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19.
  • Karlsson, Tobias, et al. (författare)
  • Sensing abilities of embedded vertically aligned carbon nanotube forests in structural composites: From nanoscale properties to mesoscale functionalities
  • 2023
  • Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368 .- 1879-1069. ; 255
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, Vertically Aligned Carbon Nanotube (VACNT) forests are embedded into two different glass fibre/epoxy composite systems to study their sensing abilities to strain and temperature. Through a bottom-up approach, performing studies of the VACNT forest and its individual carbon nanotubes on the nano-, micro-, and mesoscale, the observed thermoresistive effect is determined to be due to fluctuation-assisted tunnelling, and the linear piezoresistive effect due to the intrinsic piezoresistivity of individual carbon nanotubes. The VACNT forests offer great freedom of placement into the structure and reproducibility of sensing sensitivity in both composite systems, independent of conductivity and volume fraction, producing a robust sensor to strain and temperature.
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20.
  • Shan, Bo, et al. (författare)
  • Preparation of graphene/aligned carbon nanotube array composite films for thermal packaging applications
  • 2019
  • Ingår i: Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 58
  • Tidskriftsartikel (refereegranskat)abstract
    • Vertically aligned carbon nanotube arrays (VACNTs) have been successfully achieved by CVD. The carbon nanotubes were almost triple-walled. Furthermore, the graphene/VACNT composite films have been prepared as thermal interface materials, using photolithographic and densification processes. Compared with pure epoxy resin, the longitudinal thermal conductivity of the composite films was obviously improved, which confirmed that VACNTs provided additional longitudinal heat transfer channels in the films. Furthermore, their longitudinal thermal conductivity was largely dependent on the distribution of VACNTs. The transversal thermal conductivity of the composite film with a pattern size of 300 mu m was about seven times higher than that of pure epoxy resin. This indicated that graphene provided additional horizontal heat transfer channels to achieve the enhancement of transversal thermal conductivity in composite films. (C) 2019 The Japan Society of Applied Physics
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21.
  • Wang, Ying, et al. (författare)
  • Epoxy composite with high thermal conductivity by constructing 3D-oriented carbon fiber and BN network structure
  • 2021
  • Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 11:41, s. 25422-25430
  • Tidskriftsartikel (refereegranskat)abstract
    • As electronic devices tend to be integrated and high-powered, thermal conductivity is regarded as the crucial parameter of electronic components, which has become the main factor that limits the operating speed and service lifetime of electronic devices. However, constructing continuous thermal conductive paths for low content particle fillers and reducing interface thermal resistance between fillers and matrix are still two challenging issues for the preparation of thermally conductive composites. In this study, 3D-oriented carbon fiber (CF) thermal network structures filled with boron nitride flakes (BN) as thermal conductive bridges were successfully constructed. The epoxy composite was fabricated by thermal conductive material with a 3D oriented structure by the vacuum liquid impregnation method. This special 3D-oriented structure modified by BN (BN/CF) could efficiently broaden the heat conduction pathway and connected adjacent fibers, which leads to the reduction of thermal resistance. The thermal conductivity of the boron nitride/carbon fiber/epoxy resin composite (BN/CF/EP) with 5 vol% 10 mm CF and 40 vol% BN reaches up to 3.1 W m(-1) K-1, and its conductivity is only 2.5 x 10(-4) S cm(-1). This facile and high-efficient method could provide some useful advice for the thermal management material in the microelectronic field and aerospace industry.
  •  
22.
  • Banerjee, Debashree, et al. (författare)
  • Elevated thermoelectric figure of merit of n-type amorphous silicon by efficient electrical doping process
  • 2018
  • Ingår i: Nano Energy. - : Elsevier BV. - 2211-2855 .- 2211-3282. ; 44, s. 89-94
  • Tidskriftsartikel (refereegranskat)abstract
    • The currently dominant thermoelectric (TE) materials used in low to medium temperature range contain Tellurium that is rare and mild-toxic. Silicon is earth abundant and environment friendly, but it is characterized by a poor TE efficiency with a low figure of merit, ZT. In this work, we report that ZT of amorphous silicon (a-Si) thin films can be enhanced by 7 orders of magnitude, reaching ∼0.64 ± 0.13 at room temperature, by means of arsenic ion implantation followed by low-temperature dopant activation. The dopant introduction employed represents a highly controllable doping technique used in standard silicon technology. It is found that the significant enhancement of ZT achieved is primarily due to a significant improvement of electrical conductivity by doping without crystallization so as to maintain the thermal conductivity and Seebeck coefficient at the level determined by the amorphous state of the silicon films. Our results open up a new route towards enabling a-Si as a prominent TE material for cost-efficient and environment-friendly TE applications at room temperature.
  •  
23.
  • Wójcik, Natalia A., et al. (författare)
  • The influence of Be addition on the structure and thermal properties of alkali-silicate glasses
  • 2019
  • Ingår i: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 521
  • Tidskriftsartikel (refereegranskat)abstract
    • Be-Na-(Li)-Si oxide glasses containing up to 15 mol% of BeO were prepared. Their structure was characterized by X-ray powder diffraction and Raman as well as infrared spectroscopic techniques, while their chemical compositions were examined by Inductively Coupled Plasma Optical Emission Spectrometry. All materials were found to be amorphous and contain Al contaminations from minor dissolution of the alumina crucibles. The results of Raman and IR spectroscopies showed that BeO addition to Na-(Li)-Si glass systems resulted in the formation of [BeO4/2](2-) tetrahedra which are inserted into the silicate glass network, demonstrating the intermediate glass-forming role of BeO. In parallel, the effective destruction of Si-O-Si bridges was observed by vibrational spectroscopy. The glass transition temperature was studied by Differential Thermal Analysis and found to range from about 431 degrees C to 551 degrees C. A significant increase in T-g by 70 degrees C was found as SiO2 was substituted by up to 15 mol% BeO.
  •  
24.
  • Bojestig, Eric, 1991, et al. (författare)
  • Laser powder bed fusion of bronze - Process optimization and influence on microstructure and mechanical properties
  • 2019
  • Ingår i: Euro PM 2019 Congress and Exhibition.
  • Konferensbidrag (refereegranskat)abstract
    • As the interest in additive manufacturing increases, so does the demand for new materials. Among these are the copper alloys due to their good bearing properties, corrosion resistance and electrical conductivity. When attempting to print Cu-base materials with laser powder bed fusion, their low laser absorption and high thermal conductivity restricts the attainable local heat absorption in the material and hence the manufacturability with respect full density processing, especially for pure Cu. Alloyed Cu constitutes, however, less challenge in this respect. Hence, spherical gas atomized bronze (Cu-11Sn) powder was used and all printing was performed in an EOS M100 machine in argon atmosphere. Design of experiment method was used to determine optimized process parameters with respect to laser power, scan speed and hatch distance. Full density (99.9%) parts were successfully fabricated with UTS>400 MPa and the fine cellular microstructure was displayed. Furthermore, thin wall capacity of 150 µm was demonstrated.
  •  
25.
  • Cabo Rios, Alberto, 1990, et al. (författare)
  • Sintering anisotropy of binder jetted 316L stainless steel: part I–sintering anisotropy
  • 2022
  • Ingår i: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 65:4, s. 273-282
  • Tidskriftsartikel (refereegranskat)abstract
    • In Binder Jetting (BJ) Additive Manufacturing (AM), green components are usually subjected to sintering process to reach required properties. Owing to the inherent low green density, binder jetted (BJ) parts undergo shrinkages up to 20%. In addition, anisotropic dimensional evolution during sintering is characteristic for BJ, generally caused by the specifics of the arrangement of particles during the printing process. In this study, the multi-axial dimensional evolution of 316L stainless steel cubic samples (10 × 10 × 10 mm3), manufactured using BJ, was characterised by dilatometry experiments. Dilatometry tests were conducted up to sintering temperatures of 1300°C and 1370°C, with a heating rate of 10°C/min and 5°C/min, respectively. Dilatometry results and final dimension measurements showed anisotropic shrinkage behaviour during sintering with about 15% larger shrinkage along the building direction. Shrinkages along the other two orthogonal directions were relatively similar, but a slightly larger final shrinkage along the printhead movement direction was observed. Relative density of 85.0% and 96.4% was obtained after sintering tests at 1300°C and 1370°C, respectively.
  •  
26.
  • Hu, Q., et al. (författare)
  • Anomalous thermal expansion in the deep super-cooled liquid region of a ZrCuAlAg bulk metallic glass
  • 2018
  • Ingår i: Materials Research Letters. - : Informa UK Limited. - 2166-3831. ; 6:2, s. 121-129
  • Tidskriftsartikel (refereegranskat)abstract
    • Bulk metallic glasses (BMGs), like other glasses, soften in the super-cooled liquid region (SCLR). Here in this work, surprisingly, a large expansion is reported occurring in the deep SCLR of a Zr 47 Cu 37 Al 8 Ag 8 BMG. Nano-crystals (NCs) are found precipitated during the anomalous expansion of Zr 47 Cu 37 Al 8 Ag 8 , but also in the SCLR of Zr 43 Cu 41 Al 8 Ag 8 that exhibits a conventional softening. It is found that there is a steep composition and density change at the NCs/amorphous matrix transition region in the former alloy, and this transition region exerts a thermal stress of about 0.15 MPa to the surrounding super-cooled liquid (SCL) and drives the soft SCL to expand severely. (Figure presented) IMPACT STATEMENT An anomalous expansion, and particularly a large expansion instead of softening, is reported occurring in the deep SCLR of a Zr-based bulk metallic glass for the first time.
  •  
27.
  • Li, Yanling, 1990, et al. (författare)
  • Thermomechanical Creep in Sensitive Clays
  • 2018
  • Ingår i: Journal of Geotechnical and Geoenvironmental Engineering - ASCE. - 1090-0241 .- 1943-5606. ; 144:11
  • Tidskriftsartikel (refereegranskat)abstract
    • A systematic series of temperature-controlled oedometer tests on intact and remolded samples of sensitive clay from two depths has been performed. The focus is on studying the temperature effects on the emerging creep rate for a relatively small temperature range, that is, 5 degrees C-25 degrees C, during incremental heating and decremental cooling tests with steps of 5 degrees C. An efficient testing scheme has been developed that exploits the simultaneous testing of several samples. Furthermore, the testing scheme is designed such that no excess pore pressures are generated in the samples during temperature change. The creep rate for intact samples proved to be very sensitive to a temperature change, with the largest effects found for stress levels above the apparent preconsolidation pressure. Heating increments showed larger increases in creep rate than cooling decrements. Both, however, led to a significant change of creep rate in the intact clay samples. In contrast, the reference tests on remolded samples of the same clay that were reconstituted to the in-situ stress state did not show much sensitivity to temperature change. The latter leads to the conclusion that the significant thermal creep triggered in sensitive clays is primarily an effect of the apparent bonding of the natural clay.
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28.
  • Manchili, Swathi Kiranmayee, 1987, et al. (författare)
  • Comparative study on the densification of chromium pre-alloyed powder metallurgy steel through nanopowder addition using design of experiments
  • 2021
  • Ingår i: Results in Materials. - : Elsevier BV. - 2590-048X. ; 10
  • Tidskriftsartikel (refereegranskat)abstract
    • There is a constant demand for high density press and sinter powder metallurgical components for automotiveapplications. Steel powder pre-alloyed with chromium is an attractive material for such applications, but newways to further increase the sinter density are required for successful processing of these powders to high density.Nanopowder could be used as a potential sintering aid in order to boost the densification of the steel powdercompact. In this study, steel powder pre-alloyed with chromium, without and with admixed nickel, is used as basepowder, to which nanopowder was added. Surface oxide removal, crucial for successful sintering of such mate-rials, was studied by thermogravimetry analysis in order to understand the influence of nanopowder addition onthe oxide reduction. Powder compacts containing nanopowder showed higher mass loss in comparison to the oneswithout nanopowder. Linear shrinkage obtained from dilatometric curves increased with the addition of nano-powder. To depict the influence of the critical parameters; sintering temperature, powder size, addition ofnanopowder and composition (with or without nickel), a design of experiment approach was applied. The criticalparameters were then adjusted at 2 different values (categorical parameters) and a‘full factorial design model’was used involving 16 experiments, with sinter density and hardness as output measures of the experimentsdetermined. The results were analyzed using polynomialfit to determine which of the parameter exerts themaximum influence. Presence of nickel increased the hardness whereas sintering temperature and presence ofnanopowder enhanced the sinter density. This led to the tentative design of optimum conditions that resulted inincrease in sinter density from 7.25 g/cm3(92.5% of the theoretical density) to 7.4 g/cm3(94% of the theoreticaldensity) with an addition of 5% nanopowder to Ni-containing grade when sintered at 1350 ​°C instead of 1250 ​°C.
  •  
29.
  • Reddy, S. R., et al. (författare)
  • Nanostructuring with Structural-Compositional Dual Heterogeneities Enhances Strength-Ductility Synergy in Eutectic High Entropy Alloy
  • 2019
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 9:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A lamellar (L12 + B2) AlCoCrFeNi2.1 eutectic high entropy alloy (EHEA) was severely deformed by a novel hybrid-rolling process. During hybrid-rolling, the deformation was carried out in two stages, namely cryo-rolling followed by warm-rolling at 600 °C. The strain (ε) imparted in each of these steps was identical ~1.2, resulting in a total strain of ε~2.4 (corresponding to 90% reduction in thickness). The novel processing strategy resulted in an extremely heterogeneous microstructure consisting of retained lamellar and transformed nanocrystalline regions. Each of these regions consisted of different phases having different crystal structures and chemical compositions. The novel structure-composition dual heterogeneous microstructure originated from the stored energy of the cryo-rolling which accelerated transformations during subsequent low temperature warm-rolling. The dual heterogeneous microstructure yielded an unprecedented combination of strength (~2000 MPa) and ductility (~8%). The present study for the first time demonstrated that dual structure-composition heterogeneities can be a novel microstructural design strategy for achieving outstanding strength-ductility combination in multiphase high entropy alloys.
  •  
30.
  • Seelam, Rajasekhar Reddy, et al. (författare)
  • Microstructural design by severe warm-rolling for tuning mechanical properties of AlCoCrFeNi2.1 eutectic high entropy alloy
  • 2019
  • Ingår i: Intermetallics. - : Elsevier BV. - 0966-9795. ; 114:nov.
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of severe warm-rolling and subsequent annealing on the microstructure and mechanical properties in an AlCoCrFeNi2.1 high entropy alloy consisting of a lamellar arrangement of ordered L1(2) and B2 phases was studied. For this purpose, the as-cast EHEA was severely warm-rolled up to 90% reduction in thickness at selected temperatures of 400 degrees C, 600 degrees C, and 750 degrees C. The severely warm-rolled EHEAs were further annealed at temperatures ranging from 800 degrees C to 1200 degrees C for 1 h. Warm-rolling resulted in a unique disordering behavior of the L1(2) depending on the temperature of warm-rolling. However, the B2 phase maintained the ordered structure irrespective of the warm-rolling temperature. The EHEA warm-rolled at 400 degrees C and 600 degrees C showed a predominantly lamellar microstructure, while the EHEA warm-rolled at 750 degrees C showed a novel heterogeneous microstructure featured by a mixture of lamellar and non-lamellar regions. Annealing of the 90% warm-rolled materials resulted in the formation of predominantly duplex microstructures consisting of disordered FCC and B2 phases. The EHEA warm-rolled at 400 degrees C and 600 degrees C showed high strength but rather limited ductility, which could be improved upon annealing. Remarkably, the EHEA warm-rolled at 750 degrees C showed the most outstanding properties featured by exceptional strength-ductility combination owing to the novel heterogeneous microstructure. Annealing of the heterogeneous EHEA resulted in the deterioration of the strength-ductility balance owing to the annihilation of the heterogeneous microstructure, being replaced by a microduplex structure.
  •  
31.
  • Wang, Shuping, 1987, et al. (författare)
  • Temperature evolution during the compaction of calcium silicate hydrate powders using a compression calorimeter
  • 2020
  • Ingår i: Journal of Thermal Analysis and Calorimetry. - : Springer Science and Business Media LLC. - 1388-6150 .- 1588-2926. ; 139:2, s. 863-875
  • Tidskriftsartikel (refereegranskat)abstract
    • Amorphous calcium silicate hydrate (CSH) undergoes contact-hardening property, i.e. the powder can be hardened by compression. A compression calorimeter was designed to determine the temperature evolution during the compaction of the powder. A platinum sensor (Pt100) was used as the temperature sensor and was positioned in the powder as well as in the compression die. A resolution of 0.01 °C with a sampling time of every second was used to monitor the temperature. Both theoretical calculation and simulations by COMSOL multiphysics showed that the device reliably evaluated the temperature during the compaction of CSH powders. The measurement was taken under semi-adiabatic conditions. The temperature profiles obtained from the measurement revealed the compression process and bonding development during the compaction of the powders. Finally, a linear relationship was observed between the compressive strength and the maximum temperature increase. This provides insight into the contact-hardening mechanism during the compaction of CSH powders.
  •  
32.
  • Zhang, Q., et al. (författare)
  • Mechanical property and reliability of bimodal nano-silver paste with Ag-coated SiC particles
  • 2019
  • Ingår i: Soldering and Surface Mount Technology. - 1758-6836 .- 0954-0911. ; 31:4, s. 193-202
  • Tidskriftsartikel (refereegranskat)abstract
    • © 2019, Emerald Publishing Limited. Purpose: This study aims to develop a bimodal nano-silver paste with improved mechanical property and reliability. Silicon carbide (SiC) particles coated with Ag were introduced in nano-silver paste to improve bonding strength between SiC and Ag particles and enhance high-temperature stability of bimodal nano-silver paste. The effect of sintering parameters such as sintering temperature, sintering time and the proportion of SiC particles on mechanical property and reliability of sintered bimodal nano-silver structure were investigated. Design/methodology/approach: Sandwich structures consist of dummy chips and copper substrates with nickel and silver coating bonded by nano-silver paste were designed for shear testing. Shear strength testing was conducted to study the influence of SiC particles proportions on the mechanical property of sintered nano-silver joints. The reliability of the bimodal nano-silver paste was evaluated experimentally by means of shear test for samples subjected to thermal aging test at 150°C and humidity and temperature testing at 85°C and 85 per cent RH, respectively. Findings: Shear strength was enhanced obviously with the increase of sintering temperature and sintering time. The maximum shear strength was achieved for nano-silver paste sintered at 260°C for 10 min. There was a negative correlation between the proportion of SiC particles and shear strength. After thermal aging testing and humidity and temperature testing for 240 h, the shear strength decreased a little. High-temperature stability and high-hydrothermal stability were improved by the addition of SiC particles. Originality/value: Submicron-scale SiC particles coated with Ag were used as alternative materials to replace part of nano-silver particles to prepare bimodal nano-silver paste due to its high thermal conductivity and excellent mechanical property.
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33.
  • Hooshmand, Saleh, et al. (författare)
  • Development of Ceramic Foams Containing Platinum Nanoparticles as the Catalyst
  • 2019
  • Konferensbidrag (refereegranskat)abstract
    • The exhaust gases contribute significantly to global warming, but without a catalytic converter, exhaust gases would be even more polluting. Therefore, having a catalytic metal such as platinum nanoparticles on the surface of the pore walls in ceramic foams is a practical way to remove particulate matters and to have an effective catalytic converter in one. The porous structure of the foam filters the particulate matters and the high specific surface area of the Pt nanoparticles in the pores speed up the reactions. The role of platinum is to oxidize carbon monoxide (CO) and hydrocarbons (HC) to form carbon dioxide (CO2) and water vapor (H2O). In this study, The Pt nanoparticles were coated on the surface of the thermally expandable microspheres (Expancel). The Energy-dispersive X-ray spectroscopy (EDS) and Ultraviolet-visible spectroscopy (UV-Vis) confirmed the successful adsorption of Pt on the Expancel surface. In the next step, alumina foams prepared by the gel-casting technique using Pt-coated Expancels as the sacrificial template. The EDS confirmed the successful transfer of the Pt nanoparticles to the pore walls of the foam. The morphology and the porosity of the foams were studied using SEM and X-ray microtomography. Moreover, the compressive strength of the prepared sample in form of the green body, debinded and sintered was measured.  The results showed a promising way to design ceramic-based bi-functional foams for eliminating dust and converting harmful gases to nontoxic gases simultaneously.
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34.
  • Seisenbaeva, Gulaim, et al. (författare)
  • High surface area ordered mesoporous nano-titania by a rapid surfactant-free approach
  • 2012
  • Ingår i: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22, s. 20374-20380
  • Tidskriftsartikel (refereegranskat)abstract
    • Immersion of solid nanorods of the commercial metal–organic precursor [Ti(OCH3)4]4 into boilingwater results in their rapid topotactic transformation into rod-shaped colloid crystals built up ofuniform crystalline anatase nanoparticles with average particle diameter 5.0 +/- 1 nm forming ratherregular wormhole-type mesoporosity with average pore diameter 4.1 nm and a record-high surface areaand mesopore volume of 288 m2 g-1 and 0.42 cm3 g-1 respectively. This structure emerges throughreorganization of the intermediate ordered mesoporous lamellar structure. The distance betweenlamellae is about 3 nm. They are oriented parallel to the {1 0 0} crystallographic direction in theprecursor crystals and originate most probably through contraction and densification of the layers ofprecursor molecules in the course of the process. Similar mechanisms are observed even for hydrolytictransformation of nanocrystals of other alkoxide precursors, derivatives of volatile alcohols, permittingto achieve surface area up to 350 m2 g-1. The obtained material is completely free from organics, buthighly hygroscopic. Powders produced within 3 min show very broad X-ray diffraction peaks,indicating low volume coherence domains, but continued refluxing offers a strongly improved XPDpattern after 10 min and a fully crystalline material with coherence domain equivalent to the individualparticle size after only 30 min. The latter material exhibits well defined Ti–Ti distances in the structuretypical for a crystalline anatase phase according to EXAFS spectroscopy. It displays strongphotochemical activity in destruction of methylene blue dye. When an aqueous dispersion ofsuperparamagnetic Fe3O4 nanoparticles is applied for hydrolysis the product is a magneticnanocomposite, easily and rapidly removable from solution by a magnet. The produced fully crystallineporous TiO2 possesses attractive characteristics as an adsorbent for water remediation tested throughadsorption of dichromate anions.
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35.
  • Barick, Prasenjit, et al. (författare)
  • Effect of pressure and temperature on densification, microstructure and mechanical properties of spark plasma sintered silicon carbide processed with β-silicon carbide nanopowder and sintering additives
  • 2016
  • Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 42:3, s. 3836-3848
  • Tidskriftsartikel (refereegranskat)abstract
    • The effects of applied pressure and temperature during spark plasma sintering (SPS) of additive-containing nanocrystalline silicon carbide on its densification, microstructure, and mechanical properties have been investigated. Both relative density and grain size are found to increase with temperature. Furthermore, with increase in pressure at constant temperature, the relative density improves significantly, whereas the grain size decreases. Reasonably high relative density (~96%) is achieved on carrying out SPS at 1300 °C under applied pressure of 75 MPa for 5 min, with a maximum of ~97.7% at 1500 °C under 50 MPa for 5 min. TEM studies have shown the presence of an amorphous phase at grain boundaries and triple points, which confirms the formation of liquid phase during sintering and its significant contribution to densification of SiC at relatively lower temperatures (≤1400 °C). The relative density decreases on raising the SPS temperature beyond 1500 °C, probably due to pores caused by vaporization of the liquid phase. Whereas β-SiC is observed in the microstructures for SPS carried out at temperatures ≤1500 °C, α-SiC evolves and its volume fraction increases with further increase in SPS temperatures. Both hardness and Young׳s modulus increase with increase in relative density, whereas indentation fracture toughness appears to be higher in case of two-phase microstructure containing α and β-SiC.
  •  
36.
  • Curry, Nicholas, 1984-, et al. (författare)
  • Next generation thermal barrier coatings for the gas turbine industry
  • 2011
  • Ingår i: Journal of thermal spray technology (Print). - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 20:1-2, s. 108-115
  • Tidskriftsartikel (refereegranskat)abstract
    • The aim of this study is to develop the next generation of production ready air plasma sprayed thermal barrier coating with a low conductivity and long lifetime. A number of coating architectures were produced using commercially available plasma spray guns. Modifications were made to powder chemistry, including high purity powders, dysprosia stabilized zirconia powders, and powders containing porosity formers. Agglomerated & sintered and homogenized oven spheroidized powder morphologies were used to attain beneficial microstructures. Dual layer coatings were produced using the two powders. Laser flash technique was used to evaluate the thermal conductivity of the coating systems from room temperature to 1200 °C. Tests were performed on as-sprayed samples and samples were heat treated for 100 h at 1150 °C. Thermal conductivity results were correlated to the coating microstructure using image analysis of porosity and cracks. The results show the influence of beneficial porosity on reducing the thermal conductivity of the produced coatings. © 2010 ASM International.
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37.
  • Edgren, Aina, 1995 (författare)
  • Microstructure and high temperature properties of Mo(Si,Al)2 - The effect of particle strengthening and alloying
  • 2024
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • High temperature heating processes within the steel industries result in significant emissions of CO2, primarily due to the combustion of fossil fuels. Electrification of these processes, such as through the implementation of resistive heating elements, holds great promise for reducing emissions. However, a bottleneck in the transition to a more environmentally friendly industry is related to the materials used for these heating elements. Mo(Si,Al)2 is a ceramic material commonly used for heating elements in various high temperature furnaces and is being considered for large-scale industrial-scale applications. While its oxidation properties have been extensively studied, its mechanical properties, which are crucial when increasing the size of the heating elements, have received limited attention. In this thesis, the high temperature deformation behaviour of Mo(Si,Al)2-based materials, and potential routes for their improvement, have been investigated. This work has shown that diffusion-driven grain boundary sliding is the main deformation mechanism in polycrystalline Mo(Si,Al)2, particularly in fine-grained materials. In coarse-grained materials, the slip of dislocations also contributes to deformation. Moreover, coarse-grained Mo(Si,Al)2 relaxes through the formation of low-angle grain boundaries and dynamic recrystallization. The addition of Al2O3 particles, to achieve particle strengthening, results in a competition between a negative effect from grain refinement at low fractions (up to 15 wt.%), and a positive effect from inhibition of grain boundary sliding at higher fractions. Also alloying with W, Nb, Ta, and V has been studied, among which W was the most promising alternative. The solid solubility of W in Mo(Si,Al)2 was high, and it also led to a slight improvement in high temperature strength. The solubility of the alloying elements Nb, Ta, and V was found to be low in Mo(Si,Al)2. Instead, these elements were enriched in secondary phases. Additionally, Y alloying has been explored to investigate its effect on oxidation behaviour. However, the oxide adhesion was adversely affected.
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38.
  • Ekberg, Johanna, 1987, et al. (författare)
  • The Influence of Heat Treatments on the Porosity of Suspension Plasma-Sprayed Yttria-Stabilized Zirconia Coatings
  • 2018
  • Ingår i: Journal of Thermal Spray Technology. - : Springer Science and Business Media LLC. - 1059-9630 .- 1544-1016. ; 27:3, s. 391-401
  • Tidskriftsartikel (refereegranskat)abstract
    • Suspension plasma-sprayed coatings are produced using fine-grained feedstock. This allows to control the porosity and to achieve low thermal conductivity which makes the coatings attractive as topcoats in thermal barrier coatings (TBCs). Used in gas turbine applications, TBCs are exposed to high temperature exhaust gases which lead to microstructure alterations. In order to obtain coatings with optimized thermomechanical properties, microstructure alterations like closing of pores and opening of cracks have to be taken into account. Hence, in this study, TBC topcoats consisting of 4 mol.% yttria-stabilized zirconia were heat-treated in air at 1150 °C and thereafter the coating porosity was investigated using image analysis (IA) and nuclear magnetic resonance (NMR) cryoporometry. Both IA and NMR cryoporometry showed that the porosity changed as a result of the heat treatment for all investigated coatings. In fact, both techniques showed that the fine porosity decreased as a result of the heat treatment, while IA also showed an increase in the coarse porosity. When studying the coatings using scanning electron microscopy, it was noticed that finer pores and cracks disappeared and larger pores grew slightly and achieved a more distinct shape as the material seemed to become more compact.
  •  
39.
  • Ganvir, Ashish, 1991-, et al. (författare)
  • Influence of Microstructure on Thermal Properties of Columnar Axial Suspension Plasma Sprayed Thermal Barrier Coatings
  • 2015
  • Ingår i: Proceedings of the International Thermal Spray Conference. - : ASM International. - 9781510811546 ; , s. 498-505
  • Konferensbidrag (refereegranskat)abstract
    • Suspension Plasma Spraying is a relatively new thermal spraying technique to produce advanced thermal barrier coatings. This technique enables the production of a variety of structures from highly dense, highly porous, segmented or columnar coatings. In this work a comparative study is performed on six different suspension plasma sprayed thermal barrier coatings which were produced using axial injection and different process parameters. The influence of coating morphology and porosity on thermal properties was of specific interest. Tests carried out include microstructural analysis with SEM, phase analysis using XRD, porosity calculation using Archimedes experimental setup, pore distribution analysis using mercury infiltration technique and thermal diffusivity/conductivity measurements using laser flash analysis. The results showed that columnar and cauliflower type coatings were produced by axial suspension plasma spraying process. Better performance coatings were produced with relatively higher overall energy input given during spraying. Coatings with higher energy input, lower thickness and wider range of submicron and nanometer sized pores distribution showed lower thermal diffusivity and hence lower thermal conductivity. Also, in-situ heat treatment did not show dramatic increase in thermal properties.
  •  
40.
  • Harihara Subramonia Iyer, Anand, 1990, et al. (författare)
  • Microscale fracture of chromia scales
  • 2019
  • Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 8
  • Tidskriftsartikel (refereegranskat)abstract
    • Native protective oxide scales offer resistance against corrosion for high temperature materials, which often work in extreme conditions of varying mechanical and thermal loads. The integrity of such layers is of critical importance, since their damage can lead to significant reduction in material life. Mechanical data such as fracture strain and elastic modulus are required to include oxides in material life estimation models for high temperature materials, but there is lack of such data. Their thickness is in the mm range, which makes mechanical testing for property determination difficult. Here we present a micro-mechanical testing method, based on bending of micro-cantilevers produced by focused ion beam milling, capable of circumventing the limitations of conventional approaches. We apply this method to chromia thermally grown on pure chromium, and measure fracture strains at room and high temperatures (600 °C). The measured fracture strains were found to be higher at room temperature, due to a larger fraction of transgranular fracture. Surprisingly, a large fraction of transgranular fracture was seen even in the presence of stress concentrations at grain boundaries. Removal of the stress concentrations accentuated the propensity for transgranular cracking at room temperature. Realistic values of room temperature elastic modulus were obtained as well. The observed mixed trans- and intergranular cracking points towards the need for dedicated investigations of both oxide grain boundary strength and cleavage resistance of single crystals in order to fully understand the failure mechanisms in thermally grown oxide scales.
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41.
  • Harihara Subramonia Iyer, Anand, 1990, et al. (författare)
  • Room temperature plasticity in thermally grown sub-micron oxide scales revealed by micro-cantilever bending
  • 2018
  • Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462. ; 144, s. 9-12
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose a new geometry for focused ion beam milled micro-cantilevers, which allows production of residual stress-free, isolated thin film specimens from film-substrate systems. This geometry was used to demonstrate the presence of permanent deformation in about 200 nm thick thermally grown oxide scales on a Ni-base superalloy, after applying large bending displacements in-situ in a scanning electron microscope. Stiffness measurements performed before and after the bending tests confirmed the absence of micro-cracks, leading to the conclusion that plastic deformation occurred in the oxide scale. The proposed method is extendable to other film-substrate systems and testing conditions, like non-ambient temperatures.
  •  
42.
  • Joshi, Shrikant V., 1960-, et al. (författare)
  • New Generation Ceramic Coatings for High-Temperature Applications by Liquid Feedstock Plasma Spraying : Defense, Security, Aerospace and Energy Applications
  • 2020
  • Ingår i: Handbook of Advanced Ceramics and Composites. - Cham : Springer. - 9783319732558 ; , s. 1-42
  • Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
    • Plasma spraying with liquid feedstock offers an exciting opportunity to obtain coatings with characteristics that are vastly different from those produced using conventional spray-grade powders. The two extensively investigated variants of this technique are suspension plasma spraying (SPS), which utilizes a suspension of fine powders in an appropriate medium, and solution precursor plasma spraying (SPPS), which involves use of a suitable solution precursor that can form the desired particles in situ. The advent of axial injection plasma spray systems in recent times has also eliminated concerns regarding low deposition rates/efficiencies associated with liquid feedstock. The 10–100 μm size particles that constitute conventional spray powders lead to individual splats that are more than an order of magnitude larger compared to those resulting from the fine (approximately 100 nm–2 μm in size) particles already present in suspensions in SPS or formed in situ in SPPS. The distinct characteristics of the resulting coatings are directly attributable to the above very dissimilar splats (“building blocks” for coatings) responsible for their formation. This chapter discusses the salient features associated with SPS and SPPS processing, highlights their versatility for depositing a vast range of ceramic coatings with diverse functional attributes, and discusses their utility, particularly for high-temperature applications through some illustrative examples. A further extension of liquid feedstock plasma processing to enable use of hybrid powder-liquid combinations for plasma spraying is also discussed. This presents a novel approach to explore new material combinations, create various function-dependent coating architectures with multi-scale features, and enable convenient realization of layered, composite, and graded coatings as demonstrated through specific examples.
  •  
43.
  • Mahade, Satyapal, et al. (författare)
  • Isothermal Oxidation Behavior of Gd2Zr2O7/YSZ Multilayered Thermal Barrier Coatings
  • 2016
  • Ingår i: International Journal of Applied Ceramic Technology. - : Wiley-Blackwell. - 1546-542X .- 1744-7402. ; 13:3, s. 443-450
  • Tidskriftsartikel (refereegranskat)abstract
    • Efficiency of a gas turbine can be increased by increasing the operating temperature. Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used in gas turbine applications. However, above 1200°C, YSZ undergoes significant sintering and CMAS (calcium magnesium alumino silicate) infiltration. New ceramic materials of rare earth zirconate composition such as gadolinium zirconate (GZ) are promising candidates for thermal barrier coating applications (TBC) above 1200°C. Suspension plasma spray of single-layer YSZ, double-layer GZ/YSZ, and a triple-layer TBC comprising denser GZ on top of GZ/YSZ TBC was attempted. The overall coating thickness in all three TBCs was kept the same. Isothermal oxidation performance of the three TBCs along with bare substrate and bond-coated substrate was investigated for time intervals of 10 h, 50 h, and 100 h at 1150°C in air environment. Weight gain/loss analysis was carried out by sensitive weighing balance. Microstructural analysis was carried out using scanning electron microscopy (SEM). As-sprayed single-layer YSZ and double-layer GZ/YSZ showed columnar microstructure, whereas the denser layer in the triple-layer TBC was not columnar. Phase analysis of the top surface of as-sprayed TBCs was carried out using XRD. Porosity measurements were made by water intrusion method. In the weight gain analysis and SEM analysis, multilayered TBCs showed lower weight gain and lower TGO thickness compared to single-layer YSZ.
  •  
44.
  • Weidow, J., et al. (författare)
  • Impact of crystal defects on the grain growth of cemented carbides
  • 2018
  • Ingår i: International journal of refractory metals & hard materials. - : Elsevier Ltd. - 0263-4368 .- 2213-3917. ; 72, s. 199-202
  • Tidskriftsartikel (refereegranskat)abstract
    • Two different WC-Co powder mixtures were produced through a 200 h milling process. One of these mixtures were heat treated with the aim to remove the crystal defects from the WC grains. Image analysis showed that the two powders had the same average WC grain size and grain size distributions. X-ray diffraction showed much more narrow peaks for the material produced from the heat treated powder thus interpreted to have much less crystal defects. The powder mixtures were used to produce cemented carbides. Image analyses showed a clear difference for the WC grain sizes where the material produced from the heat treated powder had a significantly smaller mean WC grain size. It is therefore concluded that the crystal defects are of importance and facilitate WC grain growth during sintering. 
  •  
45.
  • Zhang, Pimin, 1990-, et al. (författare)
  • Isothermal oxidation behavior of HVAF-sprayed NiCoCrAlY coatings : Effect of surface treatment
  • 2017
  • Ingår i: Proceedings of the International Thermal Spray Conference &amp; Exposition (ITSC 2017). - New York : Curran Associates, Inc. - 9781510858220 ; , s. 456-461
  • Konferensbidrag (refereegranskat)abstract
    • NiCoCrAlY coatings are widely used as bond coats for ceramic thermal barrier coatings (TBCs) andoxidation and corrosion protective overlay coatings in industrial gas turbines. High temperature oxidation behaviour of NiCoCrAlYs has a great influence on the coating performance and lifetime of TBCs. A promising route to decrease the oxidation rate of such coatings is post-coating surface modification which can facilitate formation of a uniform alumina scale with a considerably slower growth rate compared to the as-sprayed coatings. In this work, the effect of surface treatment by means of shot peening and laser surface melting (LSM) on the oxidation resistance of high velocity air-fuel (HVAF) sprayed NiCoCrAlY coatings was studied. Isothermal oxidation was carried out at 1000⁰C for 1000h. Results showed that the rough surface of as-sprayed HVAF sprayed coatings was significantly changed after shot peening and LSM treatment, with a compact and smooth appearance. After the exposure, the oxide scales formed on surface-treated NiCoCrAlY coatings showed different morphology and growth rate compared to those formed on as-sprayed coating surface. The oxidation behaviour of surface treated HVAF-sprayed NiCoCrAlY coatings were revealed and discussed.
  •  
46.
  • Karimi Neghlani, Paria, 1986-, et al. (författare)
  • Tailored grain morphology via a unique melting strategy in electron beam-powder bed fusion
  • 2021
  • Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 824
  • Tidskriftsartikel (refereegranskat)abstract
    • This study presents a unique melting strategy in electron beam-powder bed fusion of Alloy 718 to tailor the grain morphology from the typical columnar to equiaxed morphology. For this transition, a specific combination of certain process parameters, including low scanning speeds (400–800 mm/s), wide line offsets (300–500 μm) and a high number of line order (#10) was selected to control local solidification conditions in each melt pool during the process. In addition, secondary melting of each layer with a 90° rotation with respect to primary melting induced more vigorous motions within the melt pools and extensive changes in thermal gradient direction, facilitating grain morphology tailoring. Four different types of microstructures were classified according to the produced grain morphology depending on the overlap zone between two adjacent melt pools, i.e., fully-columnar (overlap above 40 %), fully-equiaxed (overlap below 15 %), mixed columnar-equiaxed grains, and hemispherical melt pools containing mixed columnar-equiaxed grains (overlap ~20–25 %). The typical texture was <001>; however, the texture was reduced significantly through the transition from the columnar to equiaxed grain morphology. Along with all four different microstructures, shrinkage defects and cracks were also identified which amount of them reduced by a reduction in areal energy input. The hardness was increased through the transition, which was linked to the growth of the γʺ precipitates and high grain boundary density in the fully-equiaxed grain morphology.
  •  
47.
  • Leicht, Alexander, 1987, et al. (författare)
  • Effect of scan rotation on the microstructure development and mechanical properties of 316L parts produced by laser powder bed fusion
  • 2020
  • Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 163
  • Tidskriftsartikel (refereegranskat)abstract
    • Additive manufacturing possesses appealing features for producing high-performance components, for a wide range of materials. One of these features is the ability to locally tailor the microstructure and in turn, the mechanical properties. This study investigates how the microstructure of stainless steel 316L parts produced by laser powder bed fusion are affected by alternating the laser scan orientation. The microstructure consists of large elongated grains with a fine cell substructure. This study established the correlation between the orientation of this substructure and the crystallographic orientation. The results show that by producing parts without any rotation a quite unique crystallographic orientation can be achieved. The grain structure primarily consisted of large 〈101〉 oriented grains, that were separated by thin bands of small 〈100〉 oriented grains with respect to the building direction. As rotation was added these bands were eliminated. Samples that were produced without any rotation generated the highest tensile strength (527 ± 5.4 MPa), yield strength (449 ± 2.4 MPa) and ductility (58 ± 1.3%). The lowest mechanical properties were obtained for samples that were produced using a scan rotation of 67° with the tensile strength of 485 ± 4.8 MPa, yield strength of 427 ± 5.4 MPa and ductility of 50 ± 1.3%. This indicates that cell orientation and crystallographic orientation plays an essential role in the tensile properties of 316L parts produced by laser powder bed fusion (L-PBF).
  •  
48.
  • Lindgren, Kristina, 1989, et al. (författare)
  • Cluster formation in in-service thermally aged pressurizer welds
  • 2018
  • Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 504, s. 23-28
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermal aging of reactor pressure vessel steel welds at elevated temperatures may affect the ductile-to-brittle transition temperature. In this study, unique weld material from a pressurizer, with a composition similar to that of the reactor pressure vessel, that has been in operation for 28 years at 345 °C is examined. Despite the relatively low temperature, the weld becomes hardened during operation. This is attributed to nanometre sized Cu-rich clusters, mainly located at Mo- and C-enriched dislocation lines and on boundaries. The welds have been characterized using atom probe tomography, and the characteristics of the precipitates/clusters is related to the hardness increase, giving the best agreement for the Russell-Brown model.
  •  
49.
  • Qin, Xiao, 1993, et al. (författare)
  • Recrystallization and texture evolution of warm-pilgered FeCrAl alloy tube during annealing at 850°C
  • 2022
  • Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 562
  • Tidskriftsartikel (refereegranskat)abstract
    • Recrystallization annealing of warm-pilgered FeCrAl tubes was the key to reduce the cracking and control the microstructure and properties of the cladding tube. The recrystallization and texture evolution of warm-pilgered FeCrAl tubes were investigated. The recrystallization kinetics and textural evolution during annealing were characterized using microhardness measurements and electron backscatter diffraction. The 3D-microstructure of the warm-pilgered FeCrAl tube exhibited heterogeneous deformed grains of α-fiber and γ-fiber orientation. The significant anisotropy results in different recrystallization kinetics in the axial and circumferential directions of the tube. The mirostructure maintains a stable grain size of ∼22 µm and an aspect ratio of 1.8 in the axial and circumferential directions within 0–600 min annealing time. The stable microstructure is due to the dispersion of fine Laves phase particles in the ferrite matrix. Quantitative texture analysis shows that the α-fiber texture decreased significantly and the γ-fiber increased after recrystallization. During the annealing process, the α-fiber strong point texture component {112}<110> turns into {223}<110> and the γ-fiber component {111}<110> turns into {111}<112>. The recrystallization and texture evolution of warm-pilgered FeCrAl tube is of great significance to preparation and microstructure control of final cladding tube.
  •  
50.
  • Sharma, V., et al. (författare)
  • Improved mechanical properties of a Ti-48Al alloy processed by mechanical alloying and spark plasma sintering
  • 2023
  • Ingår i: Materials Today Communications. - : Elsevier BV. - 2352-4928. ; 35
  • Tidskriftsartikel (refereegranskat)abstract
    • Bulk Ti-48Al alloy samples were prepared by the high energy ball milling (HBM) of elemental powders, followed by spark plasma sintering (SPS) of the HBM processed powders. The microstructure, phase evolution and mechanical properties of the bulk alloy were studied. The resulting TiAl + Ti3Al two phase alloy possessed an equiaxed fine grain structure, unlike the usual lamellar structure produced by arc melting. The process parameters of HBM and SPS, e.g., milling speed, milling time and sintering temperature were used to tune the phase fraction, microstructure, and grain size. A very high nanohardness of up to ∼12 GPa was obtained, ∼2.4 times higher than the corresponding value of the as-cast counterpart. The combined influence of powder size reduction during HBM, high Ti3Al phase fraction and microstructural development during SPS resulted in higher hardness, wear resistance and yield pressure. Thus, a HBM+SPS processing approach is a promising processing route for the manufacture of high hardness bulk TiAl alloys.
  •  
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