| 1. |
- Barrirero, Jenifer, 1981-
(författare)
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Eutectic Modification of Al-Si casting alloys
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aluminum alloys with silicon as the major alloying element are the most widely used aluminum casting alloys. The eutectic phase in these alloys is formed by hard and brittle silicon plates in an aluminum matrix. Such silicon plates can act as crack propagation paths deteriorating the toughness of the material. To enhance ductility, silicon can be modified to a coral-like microstructure by addition of a modifying agent. Amongst the elements proposed as modifiers, only strontium, sodium and europium induce a plate-tocoral transition, while others such as ytterbium, only refine the silicon plates. The exact mechanism for the remarkable plate-to-coral change, and the reason why certain elements only refine the structure, is still not completely understood.In this investigation, atom probe tomography and transmission electron microscopy were used to analyze and compare the crystal structure and the distribution of solute atoms in silicon at the atomic level. An unmodified alloy and alloys modified by strontium, sodium, europium and ytterbium were studied. Elements inducing silicon plate-to-coral transition were found to contain nanometer sized clusters at the defects in silicon with stoichiometries corresponding to compounds formed at the ternary eutectic reaction of each system. In contrast, the addition of ytterbium, that only refines the silicon plates, is unable to form clusters in silicon. We propose that the formation of ternary compound clusters AlSiNa, Al2Si2Sr and Al2Si2Eu at the silicon / liquid interface during solidification restrict silicon growth. The formation of clusters on silicon facets create growth steps and increase growth direction diversity. The incorporation of clusters in silicon explains the high density of crystallographic defects and the structural modification from plates to corals.The parallel lattice plane-normals 011Si // 0001Al2Si2Eu, 011Si // 610Al2Si2Eu and 111Si // 610Al2Si2Eu were found between Al2Si2Eu and silicon, and absent between Al2Si2Yb and silicon. We propose a favorable heterogeneous formation of Al2Si2Eu on silicon. The misfit between 011Si and 0002Al2Si2X interplanar spacings shows a consistent trend with the potency of modification for several elements such as strontium, sodium, europium, calcium, barium, ytterbium and yttrium.
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| 2. |
- Bock, Florian, 1994-
(författare)
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Combining ab‐initio and machine learning techniques for theoretical simulations of hard nitrides at extreme conditions
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis I focus on combining the high accuracy of first-principles calculations with modern machine learning methods to make large scale investigations of industrially relevant nitride systems reliable and computationally viable. I study the electronic, thermodynamic and mechanical properties of two families of compounds: Ti1−xAlxN alloys at the operational conditions of industrial cutting tools and ReNx systems at crushing pres-sures comparable to inner earth core conditions. Standard first-principles simulations of materials are usually carried out at zero temperature and pressure, and while many state-of-the-art approaches can take these effects into account, they are usually accompanied by a substantial increase in computational demand. In this thesis I therefore explore the possiblities of studying materials at extreme conditions using machine learning methods with extraordinary efficiency without loss of calculational accuracy. Ti1−xAlxN alloy coatings exhibit exceptional properties due to their inherent ability to spinodally decompose at elevated temperature, leading to age-hardening. Since the cubic B1 phase of Ti1−xAlxN is well-studied, available high-accuracy first-principles data served as both a benchmark and data set on which to train a machine learning interatomic potential. Using the reliable moment tensor potentials, an investigation of the accuracy and efficiency of this approach was carried out in a machine learning study. Building upon the success of this technique, implementation of a learning-on-the-fly (active learning) methodology into a workflow to determine accurate material properties with minimal prior knowledge showed great promise, while maintaining a computational demand up to two orders of magnitude lower than comparable first-principles approaches. Investigations of properties of industrially lesser desired, but sometimes present hexagonal alloy phases of Ti1−xAlxN are also included in this thesis, since knowledge and understanding of all competing phases can help guide development toward improving cutting tool lifetime and performance. Furthermore, while w-Ti1−xAlxN may not be able to compete with its cubic counterpart in terms of hardness, it shows promise for other applications due to its electronic and elastic properties. Metastable ReNx phases are high energy materials due to their covalent N-N and Re-N bonds, leading to exceptional mechanical and electronic properties. Just like diamond, the hardest and arguably most famous metastable mate-rial naturally occurring on earth, they are stabilized by extreme pressures and high temperatures, but can be quenched to ambient conditions. Understanding the formation and existence of these non-equilibrium compounds may hold the key to unlocking a new generation of hard materials. In this thesis, all currently known phases of ReNx compounds have been investigated, encompassing both experimentally observed and theoretically suggested structures. Investigations of the convex hulls across a broad pressure range were carried out, coupled with calculations of phonons in the proposed crystals to determine both energetic and dynamical stability. Overall, the studies included in this thesis focused mainly on investigation of the ground state of ReN2 at higher pressure, where experimental results were deviating from earlier theoretical predictions. Additional research focused on specifically exploring properties and stability of novel ReN6 at synthesis conditions using the active learning workflow to train an interatomic potential.
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| 3. |
- Moreno, Maiara, 1993-
(författare)
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Wear behavior of Ti1-xAlxN-based coatings during turning
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ti1-xAlxN coatings are extensively used on cutting tools used for metal cutting. In this thesis, the wear behavior of TiN, TiAlN with different Al-content, and TiAlWN and TiAlMoN coatings is investigated after turning, using electron microscopy and X-ray absorption spectroscopy techniques. An in operando study using high-energy X-ray diffraction during turning is also carried out, to understand the strain and phase evolution of TiAlN coatings during machining. The main wear mechanisms when cutting stainless steel 316L with cutting speeds from 60 m/min up to 220 m/min are investigated. The results show a difference in wear behavior with cutting speed. At low cutting speeds, adhesive wear is the main mechanism that generates coating failure, causing fracture of the coating. The higher Al-content coatings (x ≥ 0.53) perform better compared to lower Al-content coatings, likely due to a better fracture resistance. At higher cutting speeds, 220 m/min, crater wear due to abrasive wear and chemical reactions between coating and workpiece material occurs. In this case, the high temperatures achieved during turning results in formation of hexagonal (h)-AlN in Ti0.38Al0.62N coatings, which lowers their wear resistance. For TiAlMoN and TiAlWN, an improved wear behavior is observed compared to pure TiAlN, because it retards spinodal decomposition and the subsequent formation of h-AlN. Investigations of the sliding area using TEM, EDS and XANES spectra from the Ti 1s-edge reveals that there are differences in level of spinodal decomposition, thus differences in temperature, in different regions of the tool. During in operando orthogonal turning of alloy steel, spinodal decomposition was observed to take place after only 10 s of turning for the highest Al-content coatings. Decomposition occurs where the temperature of the rake face is the highest. In summary, the results achieved lead to a better understanding of the interactions between tool and workpiece material and the different wear mechanisms which may expand the application envelope for these coatings.
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| 4. |
- Salamania, Janella, 1992-
(författare)
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Defects in Titanium Aluminum Nitride-Based Thin Films
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coatings and thin films inherently contain several types of defects. This thesis aims to enhance the understanding of the relationship of defects on the growth, structure, stability, and properties of titanium aluminum nitride films synthesized by physical vapor deposition techniques.Heteroepitaxial cubic and wurtzite films in the Ti-Al-N system grown by reactive magnetron sputtering were studied in relation to their defect structures. The dislocation structures of heteroepitaxial TiN and Ti1-xAlxNy films were analyzed by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Together with atomistic simulations, it was revealed that the presence of different dislocation types in TiN enhances the metal-metal bonds which locally weakens the directionally covalent metal-N bonds. In epitaxial cubic Ti1-xAlxN films, microstrain analysis shows that increasing N-vacancies influences the strain and compositional fluctuations in as-deposited states. During spinodal decomposition induced by annealing to high temperatures, the delay in coarsening and strain correlates with the amount of N vacancies. Detailed characterization of the decomposing domains exposed the formation of stacking faults and partial dislocations as a strain-relieving mechanism which also facilitates the known cubic-to-wurtzite transformation in Ti-Al-N.Cathodic arc deposited Ti1-xAlxN films were grown by applying a low duty cycle pulsed-substrate bias and high nitrogen pressures. This resulted into films with coarse grains and low lattice defects within them, indicating a kinetically controlled route to modify the defect structures in arc-deposited films. Applying the same technique on single crystalline TiN seed layer films kinetically stabilizes a pseudomorphic growth, allowing to form a highly textured, pseudo epitaxial wurtzite Ti1-xAlxN films by arc deposition. In combination with theoretical calculations, it was revealed that w-Ti1-xAlxN films also exhibit a miscibility gap which enables spinodal decomposition and thus age hardening when annealed. Finally, magnetron sputtered nitrogen-deficient w-Ti1-xAlxNy heteroepitaxial films were shown to exhibit a decomposition route that involves the formation of coherent intermediate MAX-like phases before transforming to pure c-TiN and w-AlN phases, which results to continued age hardening up to 1200°C.The findings in this work increase the fundamental understanding of the role of defects in Ti-Al-N films and open new routes for defect-based engineering strategies.
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| 5. |
- Wu, Zhixing, 1990-, et al.
(författare)
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Conducting Polymer‐Based e‐Refinery for Sustainable Hydrogen Peroxide Production
- 2023
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Ingår i: Energy & Environmental Materials. - : Wiley-Blackwell. - 2575-0356.
-
Tidskriftsartikel (refereegranskat)abstract
- Electrocatalysis enables the industrial transition to sustainable production of chemicals using abundant precursors and electricity from renewable sources. De-centralized production of hydrogen peroxide (H2O2) from water and oxygen of air is highly desirable for daily life and industry. We report an effective electrochemical refinery (e-refinery) for H2O2 by means of electrocatalysis-controlled comproportionation reaction (2(H)O + O -> 2(HO)), feeding pure water and oxygen only. Mesoporous nickel (II) oxide (NiO) was used as electrocatalyst for oxygen evolution reaction (OER), producing oxygen at the anode. Conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) drove the oxygen reduction reaction (ORR), forming H2O2 on the cathode. The reactions were evaluated in both half-cell and device configurations. The performance of the H2O2 e-refinery, assembled on anion-exchange solid electrolyte and fed with pure water, was limited by the unbalanced ionic transport. Optimization of the operation conditions allowed a conversion efficiency of 80%.
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| 6. |
- Wu, Zhixing, 1990-
(författare)
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Mesoporous transition metal oxides for oxygen electrocatalysis in energy conversion technologies
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrocatalysis, the foundation of electrical to chemical energy transformation, enables the mitigation of the electrical energy losses during reactions and the control of selectivity of the process to certain chemical products. The slow rate and the multi-step complexity of oxygen-associated reactions, namely oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), motivate the use of platinum group metals (PGM) catalysts, which significantly increase the price of the technologies due to the cost and scarcity of PGM-based materials. This thesis aims to fundamentally understand the electrocatalytical aspects of oxygen-associated reactions and their relevance to sustainable technologies by development of cheap and abundant materials.In this work, hydrothermal treatment routes are developed for synthesis of mesoporous MOx (M = Cr, Fe, Co, Ni, Ce) and NiCo2O4 as water-processable oxygen electrocatalysts. Firstly, anionic surfactant templated mesoporous NiO shows the lowest voltage loss with the highest turnover frequency for OER in consequence of the most accessible active sites among of nanoporous nickel (II) oxide (Paper I). It is observed that nickel and cobalt oxides are efficient bifunctional oxygen electrocatalysts compared to other investigated metal oxides. This stems from the lower voltage loss and by the presence of surface adsorbed hydroxyl species. In situ quantification shows that hydrogen peroxide is either the terminal product or the intermediate for ORR on meso-Cr2O3 and on other electrocatalysts, respectively (Paper II). In Paper IV, mesoporous NiO and NiCo2O4 are synthesized by using a template-free hydrothermal route, and NiCo2O4 performs more efficient bifunctional oxygen catalysts compared to NiO. It is found that ORR on mesoporous NiO and NiCo2O4 follow (2+1)e- and 4e-ORR path, with hydroxyl radical and hydroxyl ion as terminal products, respectively.Integrating the ORR and OER in electrochemical cells enables the study and development of energy conversion technologies. The bifunctional oxygen activity of meso-NiO is demonstrated in a PGM-free oxygen pump fed with air and water, resulting in a low faradic efficiency due to limited triple reaction points (Paper II). The performance of the oxygen pump has been significantly improved by exchanging the catalyst to mesoporous NiCo2O4 and the anolyte to concentrated KOH. The same setup is used for synthesis of the hydroxyl radical using mesoporous NiO. The hydroxyl radical is identified using degradation of rhodamine B, and a degradation rate of 0.034 min−1 is obtained in Paper IV. Additionally, two effective 2e-ORR electrocatalysts of porous organic conducting polymer poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) (Paper III) and mesoporous chromium (Paper V) have been studied for electrochemical refinery H2O2 by electrocatalysis-controlled comproportionation reaction (2?2? + ?2 → 2?2?2). It is observed that the hydrogen peroxide as terminal product of oxygen reduction shows ~70% Faradic efficiency on these two materials. The optimization of operation conditions on PEDOT: PSS-based hydrogen peroxide electrolyzer allows the conversion efficiency of 80% below 1V cell voltage. The optimized meso-Cr2O3-based hydrogen peroxide electrolyzer enables the conversion efficiency up to 90% that can be assigned to the suppressed of deterioration of catalyst.To summarize, this thesis has developed mesoporous metal oxides use as PGM-free electrocatalysts for investigating oxygen-associated reactions in the alkaline condition. Furthermore, the work has explored the energy conversion applications using the functionality of the developed oxygen electrocatalysts.
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| 7. |
- Atakan, Aylin, 1984-
(författare)
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Mesoporous material systems for catalysis and drug delivery
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hybrid material systems possess multi-functional properties which make them intriguing for the materials science community since very early dates. However, it is not straightforward to produce such material systems. A smart and efficient approach is necessary to extract the desired properties of each component under the desired conditions. This study evolved to its last form primarily around this notion, where the development of a hybrid material is the core of the work. This hybrid material is then further explored for two different applications in the catalysis and drug delivery fields.A nanoassembly was established around a mesoporous silica support. SBA-15 was picked as this support among the other mesoporous silica due to its well-defined pore structure and accessible pore volume. The silica framework was doped with Zr atoms and the pores were partly infiltrated with Cu nanoparticles resulting in a hybrid material with tunable properties. SBA-15 was synthesized by a sol-gel method where a micellar solution was employed as a template for the silica framework. To achieve the doped version, a Zr precursor was added to the synthesis solution. The effects of different synthesis conditions, such as the synthesis catalyst (F-or a Cl-salt) and the Si source (tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS)) on the characteristics of the final material were investigated. It was observed that these changes in the synthesis conditions yielded different particle morphology, pore size (11-15 nm), and specific surface area (400-700 m2/g). Cu nanoparticles (NPs) were grown in the (Zr-)SBA-15 support using infiltration (Inf) or evaporation induced wetness impregnation (EIWI) methods. The infiltration method is based on functionalizing the (Zr-)SBA-15 support surfaces before the Cu ion attachment whereas EIWI is based on slow evaporation of the liquid from the (Zr-)SBA-15 - Cu aqueous suspension. Both methods are designed to yield preferential growth of Cu NPs in the pores with a diameter smaller than 10 nm and in oxidized form. However, depending on the loading method used, different chemical states of the final material were achieved, i.e. Zr content and porous network properties are different. Cu-Zr-SBA-15 nanoassemblies produced under various synthesis conditions were used for the catalytic conversion of CO2into valuable fuels such as methanol and dimethyl ether (DME). The effect of different chemical states of the catalyst arising from variations in the synthesis parameters was investigated. It was found that the Si precursor (TEOS or SMS) had a considerable impact on the overall performance of the catalyst whereas the Cu loading method (Inf or EIWI) changed the catalytic selectivity between DME and methanol. The activity of the catalyst was further investigated in a time-evolution study where the accumulation of each product in the gas phase and the molecular groups attached to the catalyst surface were recorded over time. Accordingly, thermodynamic equilibrium was achieved on the 14th day of the reaction under 250°C and 33 bar. The resulting total CO2conversion was 24%, which is the thermodynamically highest possible conversion, according to theoretical calculations. It was also concluded from the experimental results that, DME is formed by a combination of two methoxy surface groups. Additionally, the formation of DME boosts the total CO2conversion to fuels, which otherwise is limited to 9.5%.The design of Cu-Zr-SBA-15 was also investigated for drug delivery applications, due to its potential as a biomaterial, e.g., a filler in dental composites, and the antibacterial properties of Cu. Also, the bioactivity of SiO2and ZrO2was considered to be an advantage. With this aim, Cu infiltrated Zr doped SBA-15 material was prepared by using TEOS as the silica precursor and the Inf-method to grow Cu NPs. The performance of the final material as a drug delivery vehicle was tested by an in-vitro delivery study with chlorhexidine digluconate.The nanoassemblies show a drug loading capacity of 25-40% [mg drug / mg (drug+carrier)]. The drug release was determined to be composed of two steps. First, a burst release of the drug molecules that are loosely held in the voids of the mesoporous carrier followed by the diffusion of the drug molecules that are attached to the carrier surface. The presence of Zr and Cu limits the burst release and beneficially slows down the drug release process. The effect of pore properties of SBA-15 was explored in a study where the antibiotic doxycycline hyclate was loaded in SBA-15 materials with different pore sizes. It was observed that the pore size is directly proportional to the drug loading capacity [mg drug / mg (drug+carrier)] and the released drug percentage (the released drug amount/total amount of loaded drug). The drug release was fast due to its weak interactions with the SBA-15 materials. In summary, this work demonstrates the multifunctional character of a smart-tailored nanoassembly which gives valuable insights for two distinct applications in catalysis and drug delivery.
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| 8. |
- Calamba, Katherine M., 1988-
(författare)
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Phase stability and defect structures in (Ti,Al)N hard coatings
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study highlights the role of nitrogen vacancies and defect structures in engineering hard coatings with enhanced phase stability and mechanical properties for high temperature applications. Titanium aluminum nitride (Ti,Al)N based materials in the form of thin coatings has remained as an outstanding choice for protection of metal cutting tools due to its superior oxidation resistance and high-temperature wear resistance. High-temperature spinodal decomposition of metastable (Ti,Al)N into coherent c-TiN and c-AlN nm-sized domains results in high hardness at elevated temperatures. Even higher thermal input leads to transformation of c-AlN to w-AlN, which is detrimental to the mechanical properties of the coating. One mean to delay this transformation is to introduce nitrogen vacancies.In this thesis, I show that by combining a reduction of the overall N-content of the c-(Ti,Al)Ny (y < 1) coating with a low substrate bias voltage during cathodic arc deposition an even more pronounced delay of the c-AlN to w-AlN phase transformation is achieved. Under such condition, age hardening is retained until 1100 ˚C, which is the highest temperature reported for (Ti,Al)N films. During cutting operations, the wear mechanism of the cathodicarc-deposited c-(Ti0.52Al0.48)Ny with N-contents of y = 0.92, 0.87, and 0.75 films are influenced by the interplay of nitrogen vacancies, microstructure, and chemical reactions with the workpiece material. The y = 0.75 coating contains the highest number of macroparticles and has an inhomogeneous microstructure after machining, which lower its flank and crater wear resistance. Age hardening of the y = 0.92 sample causes its superior flank wear resistance while the dense structure of the y = 0.87 sample prevents chemical wear that results in excellent crater wear resistance.Heteroepitaxial c-(Ti1-x,Alx)Ny (y = 0.92, 0.79, and0.67) films were grown on MgO(001) and (111) substrates using magnetron putter deposition to examine the details of their defect structures during spinodal decomposition. At 900 ˚C, the films decompose to form coherent c-AlN- and c-TiN- rich domains with elongated shape along the elastically soft <001> direction. Deformation maps show that most strains occur near the interface of the segregated domains and inside the c-TiN domains. Dislocations favorably aggregate in c-TiN rather than c-AlN because the later has stronger directionality of covalent chemical bonds. At elevated temperature, the domain size of (001) and (111)- oriented c-(Ti,Al)Ny films increases with the nitrogen content. This indicates that there is a delay in coarsening due to the presence of more N vacancies in the film.The structural and functional properties (Ti1-x,Alx)Ny are also influenced by its Al content (x). TiN and (Ti1-x,Alx)Ny (y = 1, x = 0.63 and x = 0.77) thin films were grown on MgO(111) substrates using magnetron sputtering technique. Both TiN and Ti0.27Al0.63N films are single crystals with cubic structure. (Ti0.23,Al0.77)N film has epitaxial cubic structure only in the first few atomic layers then it transitions to an epitaxial wurtzite layer, with an orientation relationship of c-(Ti0.23,Al0.77)N(111)[1-10]ǀǀw-(Ti0.23,Al0.77)N(0001)[11-20]. The w-(Ti0.23,Al0.77)N shows phase separation of coherent nm-sized domains with varying chemical composition during growth. After annealing at high temperature, the domains in w-(Ti0.23,Al0.77)N have coarsened. The domains in w-(Ti0.23,Al0.77)N are smaller compared to the domains in c-(Ti0.27,Al0.63)N film that has undergone spinodal decomposition. The results that emerged from this thesis are of great importance in the cutting tool industry and also in the microelectronics industry, because the layers examined have properties that are well suited for diffusion barriers.
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| 9. |
- Engberg, David L. J., 1986-
(författare)
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Atom Probe Tomography of Hard Nitride and Boride Thin Films
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hard ceramic thin films, including TiSiN, ZrAlN, ZrB2, and ZrTaB2, with applications for wear-resistant coatings, have been studied using atom probe tomography and correlated with several other analytical techniques, including X-ray diffraction, electron microscopy, and elastic recoil detection analysis. Outstanding obstacles for quantitative atom probe tomography of ceramic thin films have been surmounted.Mass spectral overlaps in TiSiN, which make 28Si indistinguishable from 14N, was resolved by isotopic substitution with 15N, and the nanostructural distribution of elements was thus revealed in 3-D, which enabled the identification of additional structural elements within the nanostructured Ti0.81Si0.1915N film. Improvements to the growth model of TiSiN by cathodic arc deposition was suggested.A self-organized nanolabyrinthine structure of ZrAlN, consisting of standing lamellae of fcc-ZrN and hexagonal AlN, was investigated with focus on the onset and limits of the self-organization. The local crystallographic orientational relationships were (001)ZrN || (0001)AlN and <110>ZrN || <2-1-10>AlN. Close to the MgO substrates, a smooth transition region was formed, going from segregated and disordered to the self-organized nanolabyrinthine structure. With increased growth temperature, coarse (111)-oriented ZrN grains occasionally precipitated and locally replaced the nanolabyrinthine structure. Significant local magnification effects rendered the Zr and N signals unusable, thereby inhibiting quantitative compositional analysis of the constituent phases, but the nanostructure was resolved using the Al signal.Ceramic materials are often affected by correlated evaporation, which can result in losses due to the detector dead-time/space. A compositional correction procedure was suggested, tested against an established procedure, and applied to ZrB2. The correction was found to be less dependent on the isotope abundances and background correction compared to the established procedure. While losses due to dead-time/space occur in atom probe tomography of all materials, the correlative field evaporation behavior of ceramics significantly increases the compositional error. The evaporation behavior of ZrB2 was therefore thoroughly investigated and evidence of preferential retention, correlated evaporation, and inhomogeneous field distributions at a low-index pole was presented. The high mass resolution, relatively low multiple events percentage, and quality of the co-evaporation correlation data was partly attributed to the crystal structure and film orientation, which promoted a layer-by-layer field evaporation.The evaporation behavior of the related ZrTaB2 films was found to be similar to that of ZrB2. The distribution of Ta in relation to Zr was investigated, showing that the column boundaries were both metal- and Ta-rich, and that there was a significant amount of Ta in solid solution within the columns.In addition, an instrumental artefact previously not described in atom probe tomography was found in several of the materials investigated in this thesis. The artefact consists of high-density lines along the analysis direction, which cannot be related to pole artefacts. The detection system of the atom probe was identified as the cause, because the artefact patterns on detector histograms coincided with the structure of the microchannel plate. Inconsistencies in the internal boundaries of the microchannel plate multifibers from the manufacturing process can influence the signal to the detector and locally increase the detection efficiency in a pattern characteristic to the microchannel plate in question.Altogether, this thesis shows that atom probe tomography of nitride and boride thin films is burdened by several artefacts and distortions, but that relevant material outcomes can nevertheless be achieved by informed choices of film isotopic constituents and analytical parameters, exclusion of heavily distorted regions (such as pole artefacts), and the use of compositional correction procedures when applicable.
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| 10. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Interface bonding of Zr1−xAlxN nanocomposites investigated by x-ray spectroscopies and first principles calculations
- 2020
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Ingår i: Physical Review Research. - College Park, MD, United States : American Physical Society. - 2643-1564. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure, chemical bonding, and interface component in ZrN-AlN nanocomposites formed byphase separation during thin film deposition of metastable Zr1−xAlxN (x = 0.0, 0.12, 0.26, 0.40) are investigatedby resonant inelastic x-ray scattering, x-ray emission, and x-ray absorption spectroscopy and compared to firstprinciples calculations including transitions between orbital angular momentum final states. The experimentalspectra are compared with different interface-slab model systems using first principles all-electron full-potentialcalculations where the core states are treated fully relativistically. As shown in this work, the bulk sensitivity andelement selectivity of x-ray spectroscopy enables one to probe the symmetry and orbital directions at interfacesbetween cubic and hexagonal crystals. We show how the electronic structure develops from local octahedralbond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results inthree different kinds of bonding originating from semicoherent interfaces with segregated ZrN and lamellar AlNnanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes placewith increasing Al content and affects the bond strength and increases resistivity.
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| 11. |
- Salamania, Janella, 1992-, et al.
(författare)
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Elucidating dislocation core structures in titanium nitride through high-resolution imaging and atomistic simulations
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 224
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Tidskriftsartikel (refereegranskat)abstract
- Although titanium nitride (TiN) is among the most extensively studied and thoroughly characterizedthin-film ceramic materials, detailed knowledge of relevant dislocation core structures is lacking. Byhigh-resolution scanning transmission electron microscopy (STEM) of epitaxial single crystal (001)-oriented TiN films, we identify different dislocation types and their core structures. These include, besidesthe expected primary a/2{110}h110i dislocation, Shockley partial dislocations a/6{111}h112i and sessileLomer edge dislocations a/2{100}h011i. Density-functional theory and classical interatomic potentialsimulations complement STEM observations by recovering the atomic structure of the different disloca-tion types, estimating Peierls stresses, and providing insights on the chemical bonding nature at the core.The generated models of the dislocation cores suggest locally enhanced metal–metal bonding, weakenedTi-N bonds, and N vacancy-pinning that effectively reduces the mobilities of {110}h110i and {111}h112idislocations. Our findings underscore that the presence of different dislocation types and their effects onchemical bonding should be considered in the design and interpretations of nanoscale and macroscopicproperties of TiN.
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| 12. |
- Salamania, Janella, 1992-, et al.
(författare)
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High-resolution STEM investigation of the role of dislocations during decomposition of Ti1-xAlxNy
- 2023
-
Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 229
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Tidskriftsartikel (refereegranskat)abstract
- The defect structures forming during high-temperature decomposition of Ti1-xAlxNy films were investigated through high-resolution scanning transmission electron microscopy. After annealing to 950 °C, misfit edge dislocations a/6〈112〉{111} partial dislocations permeate the interface between TiN-rich and AlN-rich domains to accommodate lattice misfits during spinodal decomposition. The stacking fault energy associated with the partial dislocations decreases with increasing Al content, which facilitates the coherent cubic to wurtzite structure transition of AlN-rich domains. The wurtzite AlN-rich structure is recovered when every third cubic {111} plane is shifted by along the [211] direction. After annealing to 1100 °C, a temperature where coarsening dominates the microstructure evolution, we observe intersections of stacking faults, which form sessile locks at the interface of the TiN- and AlN-rich domains. These observed defect structures facilitate the formation of semicoherent interfaces and contribute to hardening in Ti1-xAlxNy.
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| 13. |
- Schramm Benítez, Isabella Citlalli
(författare)
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Defect-engineered (Ti,Al)N thin films
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the effect of point defects (nitrogen vacancies and interstitials) and multilayering ((Ti,Al)N/TiN) on the phase transformations in cathodic arc-evaporated cubic (Ti,Al)N thin films at elevated temperatures. Special attention is paid to the evolution of the beneficial spinodal decomposition into c-TiN and c-AlN, the detrimental formation of wurtzite AlN and the potential application as hard coating in cutting tools.c-(Ti1-xAlx)Ny thin films with varying Al fractions and N content (y = 0.93 to 0.75) show a delay in the spinodal decomposition when increasing the amount of N vacancies. This results in a 300 °C upshift in the age hardening and a delay in the w-AlN formation, while additions of self-interstitials enhance phase separation. High temperature interaction between hard metal substrates and thin films is more pronounced when increasing N deficiency through diffusion of substrate elements into the film. Low N content films (y = 0.58 to 0.40) showed formation of additional phases such as Ti4AlN3, Ti2AlN, Al5Ti2 and Al3Ti during annealing and a transformation from Ti2AlN to Ti4AlN3 via intercalation. The multilayer structure of TiN/TiAlN results in surfacedirected spinodal decomposition that affects the decomposition behavior. Careful use of these effects appears as a promising method to improve cutting tool performance.
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| 14. |
- Syed, Muhammad Bilal, 1977-
(författare)
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Cathodic arc deposition process
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis aims to expand the knowledge of fundamental mechanisms that govern the cathodic arc process. The first part of this thesis explores and explains the correlations between a rather unexplored process parameter (i.e. cathode microstructure) and the microstructure of the coatings. The second part of the thesis focuses on discovering and explaining the correlations between process parameters (i.e. arc guiding magnetic field and nitrogen pressure), plasma properties (i.e. plasma density, electron temperature, ion saturation density etc.), and the microstructure of the coatings.Two aspects of the cathode microstructure are explored. The first is the cathode grain size and the second is the disparity among parent phases of the cathode in terms of work function (W.F.) and cohesive energy (C.E.).Two material systems are selected to investigate the effects of the cathode grain size on the microstructure of the coatings. In this research evolution of the microstructure of the cathode surface under the influence of arc has also been studied. The results show that for CrN coatings a decrease in average grain size of Cr cathode is beneficial in terms of reduction in macroparticle density of Cr-N coatings. In the case of powder metallurgically prepared Ti-50 at.% Al cathodes, a decrease in grain size from 1800 μm to 100 μm promotes the intermixing of Ti and Al grains at the cathode surface which resulted in lower macroparticle density of TiAlN coatings, a Ti/Al ratio closer to cathode composition, and improved hardness. However, further reduction in grain size from 100 μm to 10 μm, upon arcing favors a self-sustaining reaction between Ti and Al grains whose end product is the γ phase. This self-sustaining reaction and arc-created holelike features on the cathode surface render the coatings rich in Al and high in macroparticle density which results in reduced hardness.The research in the effects of disparity among the parent phases in terms of W.F. and C.E. of the constituents of Ti-50 at.% Al cathodes on the microstructural evolution of the converted layer and the coating's microstructure shows that the phase which has lower W.F. and C.E. suffers higher erosion. It is also shown that irrespective of the cathode type, the arc guiding magnetic field and the surface geometry of the cathode are two significant factors in controlling the microstructure of TiAlN coatings.The research in finding correlations between the arc guiding magnetic field, plasma density and the microstructure of the coatings show that for a particular arc source assembly the plasma density can be altered by just changing the strength of an electromagnet. A weaker electromagnet strength results in higher plasma density of Ti-67 at.% Al cathode which promotes the growth of dual phase TiAlN coatings, while a stronger magnetic field reduces the plasma density and promotes the growth of single phase TiAIN coatings and a reduction in deposition rate.The research in establishing the correlations between N2 pressure, plasma properties and coatings microstructure reveals that for plasma generated from Ti-50 at.% Al cathode the average charge state of Ti shows a stark increase with an increase in N2 pressure from 0 Pa to 0.07 Pa, and upon further increase in N2 pressure the average charge state gradually decreases. Moreover, the ionization of nitrogen takes place at the expense of Al2+. It has also been observed that the electron density increases with increasing the N2 pressure while the effective electron temperature decreases. Furthermore, the energetic ion flux to the coating's growth front decreases as the N2 pressure is increased which leads to the alteration of growth texture from 220 to 111.
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| 15. |
- Chen, Yu-Hsiang
(författare)
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Mechanical and thermal stability of hard nitride coatings
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hard coating’s thermal stability is essential due to the high temperature environment of high-speed cutting applications, while the phase and microstructure evolution induced by exposing the coating to high temperature affects the mechanical properties. In this thesis, the mechanical stability of arc-evaporated, hard, transition metal nitride coatings annealed at high temperature is analyzed and related to the phase and microstructure evolution. In addition to hardness, fracture toughness is evaluated by surface and cross-sectional investigations by scanning/transmission electron microscopy of damage events following mechanical tests.The crack resistance of Ti1−xAlxN with a range of Al content (x = 0.23-0.82) was studied by contact fatigue tests, where the differences in the microstructure were found to play a major role. Superior mechanical properties were found in Ti0.63Al0.37N; in the as-deposited state as a result of a favorable grain size, and after annealing at 900o C due to the microstructure formed during spinodal decomposition.The mechanical and high-temperature properties of hard coatings can be enhanced by alloying or multi-layering. Within this work, quaternary Ti-Al-X-N (X = Cr, Nb and V) alloys were studied and superior toughness was found for TiAl(Nb)N in both the as-deposited and annealed (1100◦ C) states. The hexagonal (h)-AlN formation in cubic (c)-TixAl0.37Cr1−0.37−xN (x = 0.03 and 0.16) was analyzed by in-situ x-ray scattering during annealing. The energy for h-AlN formation was found to be dependent on the microstructure evolution during annealing, which varies with the coating composition.High Al content h-ZrAlN/c-TiN and h-ZrAlN/c-ZrN multilayers were investigated through scratch tests followed by focused ion-beam analysis of the crack propagation. A c-Ti(Zr)N phase forms in h-ZrAlN/c-TiN multilayers at high temperatures and that contributes to enhanced hardness and fracture toughness by keeping the semi-coherent sub-interfaces.Finally, an in-situ analysis of coatings by x-ray scattering during a turning process was carried out. It demonstrates the possibility of observation of stress evolution and thermal expansion of the coatings or the work piece material during machining. This experiment provides real-time information on the coating behavior during cutting.
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