| 1. |
- Fallqvist, Mikael, et al.
(författare)
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Nucleation And Growth Of Cvd α-Al2O3 On TiXOY Template
- 2012
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 207, s. 254-261
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure, phase and chemical composition of TixOy templates used to nucleate α-Al2O3 on Ti(C,N) coated cemented carbide have been elucidated using scanning electron microscopy, X-ray diffraction, Auger electron spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry. Further, the adhesive strength of the α-Al2O3–TixOy–Ti(C,N) interfaces was investigated using scratch adhesion testing.The present study confirmed that the as-deposited template consisted of a Ti4O7 phase which during subsequent deposition of the Al2O3 layer transformed to a Ti3O5 phase and that the grown Al2O3 layer consisted of 100% α-Al2O3. Furthermore, the results showed that the lowest interfacial strength within the multilayer structure was exhibited by the Ti(C,N)–TixOy interface and that the transformation of Ti4O7 to Ti3O5 in the template resulted in formation of pores in the Ti(C,N)-template interface lowering the interfacial strength even more. The use of surface analysis techniques such as Auger electron spectroscopy and especially Time-of-Flight Secondary Ion Mass Spectrometry enabled trace element analyses using depth profiling to characterise the thin interfacial layers in detail.
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| 2. |
- Bexell, Ulf, et al.
(författare)
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Bonding of vegetable oils to mercapto silane treated metal surfaces : Surface engineering on the nano scale
- 2006
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:2, s. 838-841
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Tidskriftsartikel (refereegranskat)abstract
- In this paper the bonding of thin vegetable oil films on mercapto silane treated aluminium surfaces has been studied. The silane molecules are attached to the surface by metal-oxygen-silicon bonds. The coupling between the unsaturated bonds of the vegetable oil and the thiol functionalised surface was obtained through a photoinduced thiol-ene reaction. The surfaces were characterised by X-ray photoelectron spectroscopy (XPS). Vegetable oil contains both saturated and unsaturated carbon chains. For the reactions investigated in this study it is the unsaturated carbon chains that can react by a thiol-ene reaction and the results indicate that it is possible to attach a vegetable oil to a metal surface pre-treated with a thiol functionalised silane.
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| 3. |
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| 4. |
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| 5. |
- Engkvist, Josefin, et al.
(författare)
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Early stages of oxidation of uncoated and PVD SiO2 coated FeCrAl foils
- 2009
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 203:19, s. 2845-2850
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Tidskriftsartikel (refereegranskat)abstract
- The high temperature oxidation characteristics of uncoated and SiO2 PVD-coated FeCrAl foils have been investigated when exposed to laboratory air at 1000 °C during 1, 2, 4, 8, 16, 32 and 60 min. The oxidized samples were characterized using SEM, EDS, AES and SIMS. The results show that the presence of a 100 nm thin SiO2 PVD coating significantly reduces the oxidation rate of the FeCrAl foil during early stages of oxidation. The decreased oxidation rate displayed by the SiO2 coated FeCrAl foil is the result of the SiO2 coating acting as an initial diffusion barrier promoting the formation of a predominantly inward growing Al2O3 layer during oxidation. Additionally, by using EDS analysis together with AES and SIMS depth profiling it was shown that the total concentration of Si in the grown oxide scale decreased during oxidation.
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| 6. |
- Engkvist, Josefin, et al.
(författare)
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High temperature oxidation of FeCrAl-alloys : influence of Al-concentration on oxide layer characteristics
- 2009
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Ingår i: Materials and corrosion - Werkstoffe und Korrosion. - : Wiley. - 0947-5117 .- 1521-4176. ; 60:11, s. 876-881
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Tidskriftsartikel (refereegranskat)abstract
- The superior high temperature oxidation resistance of FeCrAl alloys relies on the formation of a dense and continuous protective aluminium oxide layer on the alloy surface when exposed to high temperatures. Consequently, the aluminium content, i.e. the aluminium concentration at the alloy–oxide layer interface, must exceed a critical level in order to form a protective alumina layer. In the present study the oxidation behaviour of six different FeCrAl alloys with Al concentrations in the range of 1.2–5.0wt% have been characterised after oxidation at 900 8C for 72 h with respect to oxide layer surface morphology, thickness and composition using scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy.The results show that a minimum of 3.2wt% Al in the FeCrAl alloy is necessary for the formation of a continuous alumina layer. For Al concentrations in the range of 2.0–3.0wt% a three-layered oxide layer is formed, i.e. an oxide layer consisting of an inner alumina-based layer, an intermediate chromia-based layer and an outer iron oxide-based layer. In contrast, the 1.2wt% Al FeCrAl alloy is not able to form a protective oxide layer inhibiting extensive oxidation.
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| 7. |
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| 8. |
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| 9. |
- Berger, Robert, et al.
(författare)
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A comparative study of the corrosion protective properties of chromium and chromium free passivation methods
- 2007
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 202:2, s. 391-397
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Tidskriftsartikel (refereegranskat)abstract
- Commercially available passivation methods for white-rust protection of hot-dip galvanized steel have been investigated. The passivations were either based on trivalent chromium or chromium free. A chromate based conversion coating was used for reference. The treated panels were tested with regard to white rust protection and paintability. The surface chemistry of the conversion coatings was monitored with scanning Auger electron spectroscopy and X-ray photoelectron spectroscopy. Coating thicknesses were measured using Auger electron sputter depth profiling. The passivations were applied with a thickness recommended by the supplier and thus showed large variation. The thickness of the chromium free passivation (Cr-free) is approximately 75 nm. The coating contains the active ions; H3O+, Ti4+, Mn2+, Zn2+, PO4 3-. The passivation based on trivalent chromium (Cr-III) is approximately 30 nm thick and contains the active ions; H3O+ Cr3+, PO4 3-, F. The chromate based passivation (Cr- VI) is approximately 5 nm thick and contains the active ions Cr6+/Cr3+, F-. The Cr-free and the Cr-III passivations showed similar white rust protection in the corrosion tests. The corrosion resistance was good although it did not fully reach the level of the Cr-VI passivation. The results from the tests of the painted panels showed that the powder paint worked well on all three passivations. The solvent born paint worked best on the passivation based on trivalent chromium. The water born paint showed poor resistance to blistering in the Cleveland humidity test for all three passivations. In this test the passivation with hexavalent chromium showed slightly better results than the chromate free passivations.
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| 10. |
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| 11. |
- Berger, Robert, et al.
(författare)
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The influence of alkali-degreasing on the chemical composition of hot-dip galvanized steel surfaces
- 2006
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Ingår i: Surface and Interface Analysis. - : Wiley. - 0142-2421 .- 1096-9918. ; 38:7, s. 1130-1138
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Tidskriftsartikel (refereegranskat)abstract
- The influence of dipping temperature and time on the surface chemistry of hot-dipped galvanized steel sheets during the alkaline degreasing process is investigated. The surface chemistry was monitored with scanning Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results show high Al concentrations on the untreated surfaces, which are significantly reduced during alkaline degreasing. The same conclusions could be drawn for the carbon compounds that accumulate on the surface during storage. The measurements reveal a gradual reduction in surface Al as the alkali solution temperature and/or degreasing time are increased. When degreasing was conducted at 70 °C for 30 s the surface was practically free from Al, which was present only in small islands. Furthermore, the experiments showed that the thickness of the oxide film covering the surfaces before and after alkaline degreasing is approximately 20 Å. The main constituents of the film varied from ZnAl hydroxide/oxide to Zn hydroxide/oxide, before and after degreasing, respectively.
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| 12. |
- Bexell, Ulf, et al.
(författare)
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A corrosion study of hot-dip galvanized steel sheet pre-treated with gamma-mercaptopropyltrimethoxysilane
- 2007
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Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 201:8, s. 4734-4742
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Tidskriftsartikel (refereegranskat)abstract
- In the present work an organofunctional silane, gamma-mercaptopropyltrimethoxysilane (gamma-MPS), has been deposited on hot-dip galvanized cold rolled steel from different silane solution concentrations. Painted and unpainted silane treated samples were corrosion tested and painted samples were adhesion tested. The surface chemistry of the unpainted silane treated samples was investigated with AES, ToF-SIMS and EDS and the surface morphology was studied with SEM. The results show that the silane film thickness is dependent on the silane concentration in the silane solution and a higher silane concentration gives a thicker film. Moreover, thicker films tend to give films with a pronounced crack pattern and even detachment of film debris. Corrosion tests of unpainted samples show that gamma-MPS can not work as a passivation treatment but gives a very good adhesion to the paint
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| 13. |
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| 14. |
- Chantziara, Katerina, 1993-, et al.
(författare)
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A case study of mechanical and thermal fatigue of press hardening dies
- 2022
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Ingår i: IOP Conference Series: Materials Science and Engineering. - : IOP Publishing. - 1757-8981 .- 1757-899X. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- Press hardening provides ultra-high strength steel components, typically boron steels, of complex geometries. In the process, the steel sheet is heated in a furnace to the austenitization temperature, transferred to the press, then simultaneously formed at high temperature and cooled in the die. Life limiting factors for the press hardening dies are mechanical fatigue, thermal fatigue, and wear. In the present case study two die segments were selected where critical damages were mechanical and thermal fatigue, respectively. The dies were made of a H13 type premium hot-work tool steel with complex heated die technology, die design integrating an advanced cooling system, for pressing automotive frame parts.The first die failed due to mechanical loading with a crack initiated from the ejector pin area. The die design, the mechanical loads, the elevated temperature, and the tool steel crack resistance are main factors to consider. In the second die cracks initiated from an ejector pin hole, as well, due to thermal cycles causing alternating compressive and tensile stresses at the surface, which led to crack nucleation because of the accumulation of local plastic strain in the surface.
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| 15. |
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| 16. |
- Engberg, Göran, et al.
(författare)
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Analysis of the plastic deformation behavior for two austenitic NiCr-steels with different stacking fault energies
- 2018
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Ingår i: International Journal of Computational Physics Series. - : NSSEL Publishing. - 2631-8350. ; 1:1, s. 137-141
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Tidskriftsartikel (refereegranskat)abstract
- Two austenitic stainless steels, with low and medium stacking fault energies (SFE), 20 mJ/m2 and 30 mJ/m2 respectively, have been studied by conventional tensile tests and in situ tensile tests in a FEG-SEM equipped for EBSD. High angle boundaries (HAB) and low angle boundaries (LAB) with misorientations >= 10o and >= 2o respectively have been determined, and size distributions for the LABs have been derived by linear intercepts. It was found that the size distributions could be described by bimodal lognormal functions. For the steel with highest SFE plastic deformation took place by dislocation slip only while the steel with low SFE deformed by slip and twinning. Using a model for slip based on the evolution of the dislocation density with the generation of dislocations inversely proportional to the mean free distance of slip and recovery of dislocations proportional to the dislocation density the stress strain-curves were analyzed and the results compared with the measured quantities. The mean free distance of slip as evaluated from the stress-strain curve for the steel with the highest SFE correlates very well with the mean size of the LABs intercept. The rate of recovery also gave an expected stress dependence. The stress needed to start deformation twinning was based on the assumption that Shockley partials become completely separated in the slip plane. The thus calculated values for the twinning stress showed an excellent agreement with the observed start of twinning as given by EBSD evaluation of twin boundaries (TB). For the alloy with low SFE both surface grains (in situ test) and bulk grains (from interrupted conventional tests) were studied. The stress needed for slip and twinning of surface grains was, as expected, in the order of 0.5-0.6 times the applied stress.
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| 17. |
- Grehk, Mikael, et al.
(författare)
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Initial stages of metal-organic chemical-vapor deposition of ZrO2 on a FeCrAl alloy
- 2008
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Ingår i: Thin Solid Films. - Amsterdam : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:6, s. 875-879
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Tidskriftsartikel (refereegranskat)abstract
- The initial stages of metal-organic chemical-vapor deposition of ZrO2 on a model FeCrAl alloy was investigated using synchrotron radiation photoelectron spectroscopy, X-ray absorption spectroscopy, scanning Auger microprobe, and time of flight secondary mass spectrometry. The coatings were grown in ultra-high vacuum at 400 degrees C and 800 degrees C using the single source precursor zirconium tetra-tert-butoxide. At 400 degrees C the coatings mainly consist of tetragonal ZrO2 and at 800 degrees C a mixed ZrO2/Al2O3 layer is formed. The Al metal diffuses from the FeCrAl bulk to the metal/coating interface at 400 degrees C and to the surface of the coating at 800 degrees C. The result indicates that the reaction mechanism of the growth process is different at the two investigated temperatures.
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| 18. |
- Grehk, Mikael, et al.
(författare)
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Investigation of the drying process of linseed oil using FTIR and ToF-SIMS
- 2008
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Ingår i: Proceedings of the 17th International Vacuum Congress/13th International Conference on Surface Science/Internatinal Conference on Nanoscience and Technology. - Stockholm : IOP Publishing.
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Konferensbidrag (refereegranskat)abstract
- The drying process of linseed oil, oxidized at 80 oC, has been investigated with rheology measurements, Fourier transformation infrared spectroscopy (FTIR), and time of flight secondary ion mass spectrometry (ToF-SIMS). The drying process can be divided into three main steps: initiation, propagation and termination. ToF-SIMS spectra show that the oxidation is initiated at the linolenic (three double bonds) and linoleic fatty acids (two double bonds). ToF-SIMS spectra reveal peaks that can be assigned to ketones, alcohols and hydroperoxides. In this article it is shown that FTIR in combination with ToF-SIMS are well suited tools for investigations of various fatty acid components and reaction products of linseed oil.
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| 19. |
- Grehk, Mikael, et al.
(författare)
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Li-induced phase transition from the Ge(111)3x1:Li surface reconstruction to the Ge(111)rot3xrot3:Li lithium germanid
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 61:7, s. 4963-4967
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the Li-induced phase transition from the Ge(111)3×1:Li to the Ge(111)sqrt[3]×sqrt[3]:Li reconstruction with photoemission. The Ge(111)3×1:Li reconstruction can be described as parallel rows of Ge atoms separated by single rows of Li atoms. The Ge(111)sqrt[3]×sqrt[3]:Li reconstruction, on the other hands, has to be described in terms of a Li-germanide phase extending over at least two atomic layers.
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| 20. |
- Javadzadeh Kalahroudi, Faezeh, et al.
(författare)
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High-Nitrogen PM Tool Steel : A Comparison Of Microstructure And Mechanical Properties Of As-HIPed And HIPed Followed By Hot Working
- 2022
-
Ingår i: World PM 2022 Congress Proceedings. - : European Powder Metallurgy Association (EPMA). - 9781899072552
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High-nitrogen-chromium alloyed powder metallurgy (PM) tool steels offer many attractive features including high strength and corrosion resistance. The PM route offers various advantages such as advanced alloy composition, high homogeneity, and well-defined size distribution of hard phase particles. This study presents microstructure and mechanical properties of a PM Cr-Mo-V-N alloy. The conventional manufacturing route for this alloy is hot isostatic pressing (HIP) followed by hot working. To investigate the possibility of near-net-shape manufacturing, a comprehensive comparison of the performance was made between steels produced by as-HIPed and HIPed followed by hot working. Both steel types were heat treated in the same way to obtain martensitic matrix with limited retained austenite. In the present investigation, microstructure and phase analyses were performed by X-ray diffraction and scanning electron microscopy. Mechanical tests were carried out by hardness measurements and tensile fatigue tests in the very high cycle fatigue regime using ultrasonic fatigue testing.
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| 21. |
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| 22. |
- Javadzadeh Kalahroudi, Faezeh
(författare)
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Microstructure and Fatigue Analysis of PM-HIPed Alloys : A Focus on Inconel 625 and High-Nitrogen Tool Steel
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nickel-based superalloys and tool steels are well-known high-performance alloys due to their extensive use in many different industries. Nickel-based superalloys have found their way into aircraft, aerospace, marine, chemical, and petrochemical industries owing to their excellent high-temperature corrosion and oxidation resistance. On the other hand, tool steels could provide a combination of outstanding corrosion and wear resistance. They can play an important role in cutting and wear applications and manufacturing plastic extrusion and food processing components.Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce these alloys. This technology can successfully tackle conventional manufacturing challenges of highly alloyed materials i.e. segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries (PPBs) in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both Ni-based superalloys and tool steels may affect the fatigue performance of these PM-HIPed products.This licentiate thesis aims to investigate the microstructure and fatigue behavior of two PM-HIPed alloys i.e. Inconel 625 and high-nitrogen tool steel. The results confirm precipitation along PPBs in PM-HIPed Inconel 625; however, no effect was detected in the fractography studies of the high cycle fatigue samples, and tensile properties were comparable with wrought materials reported in the literature. On the other hand, the microstructure of PM-HIPed high-nitrogen tool steel displayed dispersed precipitates and no traces of PPBs. Moreover, in both cases, i.e. very high cycle fatigue of PM-HIPed high-nitrogen tool steel and high cycle fatigue of PM-HIPed Inconel 625, fatigue crack initiation was attributed to the presence of non-metallic inclusions, either individually or agglomerated with precipitates. This underscores the significance of the manufacturing process in fatigue performance.
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| 23. |
- Javadzadeh Kalahroudi, Faezeh, et al.
(författare)
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On the microstructure and high cycle fatigue of near-net shape PM-HIPed Inconel 625
- 2023
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 886
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigated the microstructure and fatigue behavior of PM-HIPed Inconel 625. The microstructure was composed of γ phase and (Mo, Nb) carbonitrides located mostly on prior particle boundaries. Despite the presence of these carbonitrides, the samples showed good tensile properties with high elongation. Two different surface conditions, pickled and machined, were used for high cycle fatigue testing under a four-point bending test. The results indicated that pickled samples had 6% lower fatigue strength (at 106 cycles) with three times higher standard deviation compared to the machined ones. Fatigue failure mechanisms were found to be dependent on surface conditions and showed different failure modes due to non-metallic oxide inclusions and surface defects in samples with machined and pickled surfaces, respectively. The effect of type, size, and location of defects, multiplicity of crack initiations, as well as surface roughness were analyzed and discussed.
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| 24. |
- Karimi Bakhshandi, Reza, et al.
(författare)
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Failure analysis of two cylindrical impact pistons subjected to high velocity impacts in drilling applications
- 2022
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Ingår i: Engineering Failure Analysis. - : Elsevier. - 1350-6307 .- 1873-1961. ; 140
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Tidskriftsartikel (refereegranskat)abstract
- Top hammer drilling is a common method to drill holes in rock formations in mining and civil engineering applications. Failure of drilling machine components has a significant impact on the cost and period of the operation. Internal components of percussive hammers experience extreme loading conditions during their service life. The focus of the present case study is to characterize failure mechanisms of two cylindrical impact pistons subjected to impact loading. The investi-gated components were manufactured from two different steel grades, a surface hardened low alloyed high strength steel and a through hardened cold work tool steel.Failure of both pistons started with degradation of the impact surfaces in term of cavitation erosion and localized surface fatigue phenomena. Subsequently, chipping and removal of material from impact surfaces resulted in formation of semi-spherical holes and craters on both surfaces.Radial and hoop cracks started to develop from cavities on the impact surface. The radial cracks then propagated parallel to the impacting surface in the longitudinal direction of the piston. Once the cracks formed at the impact surface, the damage was controlled by impact fa-tigue. Fatigue beach marks were identified on the fracture surface of failed component.
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| 25. |
- Karlsson, P. G., et al.
(författare)
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Metal organic chemical vapor deposition of ultrathin ZrO2 films on Si(1 0 0) and Si(1 1 1) studied by electron spectroscopy
- 2007
-
Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 601:4, s. 1008-1018
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Tidskriftsartikel (refereegranskat)abstract
- The growth of ultrathin ZrO2 films on Si(100)-(2x1) and Si(111)-(7x7) has been studied with core level photoelectron spectroscopy and X-ray absorption spectroscopy. The films were deposited sequentially by chemical vapor deposition in ultra-high vacuum using zirconium tetra-tert-butoxide as precursor. Deposition of a > 50Å thick film leads in both cases to tetragonal ZrO2 (t-ZrO2), whereas significant differences are found for thinner films. On Si(111)-(7x7) the local structure of t-ZrO2 is not observed until a film thickness of 51Å is reached. On Si(100)-(2x1) the local geometric structure of t-ZrO2 is formed already at a film thickness of 11Å. The higher tendency for the formation of t-ZrO2 on Si(100) is discussed in terms of Zr–O valence electron matching to the number of dangling bonds per surface Si atom. The Zr–O hybridization within the ZrO2 unit depends furthermore on the chemical composition of the surrounding. The precursor t-butoxy ligands undergo efficient C–O scission on Si(100), leaving carbonaceous fragments embedded in the interfacial layer. In contrast, after small deposits on Si(111) stable t-butoxy groups are found. These are consumed upon further deposition. Stable methyl and, possibly, also hydroxyl groups are found on both surfaces within a wide film thickness range.
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| 26. |
- Li, Wei, et al.
(författare)
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Generalized stacking fault energy of gamma-Fe
- 2016
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Ingår i: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 96:6, s. 524-541
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the generalized stacking fault energy ( [GRAPHICS] -surface) of paramagnetic [GRAPHICS] -Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along the [GRAPHICS] -surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking fault formation regime ( [GRAPHICS] K) towards maximum twinning ( [GRAPHICS] K) and finally to a dominating full-slip regime ( [GRAPHICS] K). Our predictions are discussed in connection with the available experimental observations.
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| 27. |
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| 28. |
- Lu, Jun, et al.
(författare)
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Stacking fault energies in austenitic stainless steels
- 2016
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 111, s. 39-46
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Tidskriftsartikel (refereegranskat)abstract
- We measure the stacking fault energy of a set of 20 at% Cr-austenitic stainless steels by means of transmission electron microscopy using the weak beam dark field imaging technique and the isolated dislocations method. The measurements are analyzed together with first principles calculations. The results show that experiment and theory agree very well for the investigated concentration range of Mn (0-8%) and Ni (11-30%). The calculations show that simultaneous relaxation of atomic and spin degrees of freedom is important in order to find the global energy minimum for these materials. Our results clearly show the great potential of the weak beam dark field technique to obtain accurate measurements of the stacking fault energy of austenitic steels and that the reliable predictability of first principles calculations can be used to design new steels with optimized mechanical properties.
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| 29. |
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| 30. |
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| 31. |
- Olofsson, Johanna, 1981-, et al.
(författare)
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Evaluation of silicon nitride as a wear resistant and resorbable alternative for total joint replacement
- 2012
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Ingår i: Biomatter. - : Landes Bioscience. - 2159-2527 .- 2159-2535. ; 2:2, s. 94-102
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Tidskriftsartikel (refereegranskat)abstract
- Many of the failures of total joint replacements are related to tribology, i.e., wear of the cup, head and liner. Accumulation of wear particles at the implants can be linked to osteolysis which leads to bone loss and in the end aseptic implant loosening. Therefore it is highly desirable to reduce the generation of wear particles from the implant surfaces.Silicon nitride (Si3N4) has shown to be biocompatible and have a low wear rate when sliding against itself and is therefore a good candidate as a hip joint material. Furthermore, wear particles of Si3N4 are predicted to slowly dissolve in polar liquids and they therefore have the potential to be resorbed in vivo, potentially reducing the risk for aseptic loosening.In this study, it was shown that α-Si3N4-powder dissolves in PBS. Adsorption of blood plasma indicated a good acceptance of Si3N4 in the body with relatively low immune response. Si3N4 sliding against Si3N4showed low wear rates both in bovine serum and PBS compared with the other tested wear couples. Tribofilms were built up on the Si3N4 surfaces both in PBS and in bovine serum, controlling the friction and wear characteristics.
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| 32. |
- Palmgren, Pål
(författare)
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Initial stages of metal- and organic-semiconductor interface formation
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis deals with the electronic and geometrical properties of metal-semiconductor and organic-semiconductor interfaces investigated by photoelectron spectroscopy and scanning tunneling microscopy. First in line is the Co-InAs interface (metal-semiconductor) where it is found that Co is reactive and upon adsorption and thermal treatment it alloys with the indium of the substrate to form metallic islands, about 20 nm in diameter. The resulting broken bonds causes As entities to form which are loosely bond to the surface and evaporate upon thermal treatment. Thus, the adsorption of Co results in a rough interface. Secondly the metal-free phthalocyanine (H2PC) - titanium dioxide interface (organic-semiconductor) is investigated. Here it is found that the organic molecules arrange themselves along the substrate rows upon thermal treatment. The interaction with the TiO2 is mainly with the valence Π-electrons in the molecule causing a relatively strong bond, but this interaction is short range as the second layer of molecules retains their molecular character. This results in an ordered adsorption but limited mobility of the molecules on the surface prohibiting well ordered close packed layers. Furthermore, the hydrogen atoms inside the cyclic molecule leave the central void upon thermal treatment. The third case is the H2PC-InAs/InSb interface (organic-semiconductor). Here ordered overlayer growth is found on both substrates where the molecules are preferentially adsorbed on the In rows in the [110] direction forming one-dimensional chains. The InSb-H2PC interface is found to be weakly interacting and the bulk-like molecular character is retained upon both adsorption and thermal treatment. On the InAs-H2PC interface, however, the interaction is stronger. The molecules are more affected by the surface bond and this effect stretches up a few monolayers in the film after annealing.
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| 33. |
- Sandell, Anders, et al.
(författare)
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Growth of ultrathin ZrO2 films on Si(100) : film-thickness-dependent band alignment
- 2007
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Ingår i: Applied Physics Letters. - : American Institute of Physics. - 0003-6951 .- 1077-3118. ; 88:13
-
Tidskriftsartikel (refereegranskat)abstract
- The band alignment of ultrathin ZrO2 films of different thickness formed on Si(100) have been monitored with synchrotron radiation photoelectron spectroscopy and x-ray absorption spectroscopy. The films were deposited sequentially by way of metal-organic chemical-vapor deposition in ultrahigh vacuum. A significant decrease in the conduction band offset is found for increasing film thickness. It is accompanied by a corresponding increase of the valence band offset. The variations originate in the formation of an interfacial layer characterized by a lower degree of Zr-O interaction than in bulk ZrO2 but with no clear evidence for partially occupied Zr 4d dangling bonds.
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| 34. |
- Yvell, Karin, et al.
(författare)
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EBSD analysis of surface and bulk microstructure evolution during interrupted tensile testing of a Fe-19Cr-12Ni alloy
- 2018
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 141, s. 8-18
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The microstructure evolution in both surface and bulk grains in a pure Fe-19Cr-12Ni alloy has been analyzed using electron backscatter diffraction after tensile testing interrupted at different strains. Surface grains were studied during in situ tensile testing performed in a scanning electron microscope, whereas bulk grains were studied after conventional tensile testing. The evolution of the deformation structure in surface and bulk grains displays a strong resemblance but the strain needed to obtain a similar deformation structure is lower in the case of surface grains. Both slip and twinning are observed to be important deformation mechanisms, whereas deformation-induced martensite formation is of minor importance. Since the stacking fault energy (SFE) is low, 17mJ/m2, dynamic recovery by cross slip of un-dissociated dislocations is unfavorable. This reduces the annihilation of dislocations which in turn leads to a significant increase of low angle boundaries with increasing strain. The low SFE also favors formation of deformation twins which reduces the slip distance, leading to a hardening similar to the Hall-Petch relation. The combination of a low ability for cross-slip and a reduced slip distance caused by twinning is concluded to be the main reason for maintaining a high strain-hardening rate up to strains close to necking.
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| 35. |
- Yvell, Karin, et al.
(författare)
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Microstructure characterization of 316L deformed at high strain rates using EBSD
- 2016
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 122, s. 14-21
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Tidskriftsartikel (refereegranskat)abstract
- Specimens from split Hopkinson pressure bar experiments, at strain rates between similar to 1000-9000 s(-1) at room temperature and 500 degrees C, have been studied using electron backscatter diffraction. No significant differences in the microstructures were observed at different strain rates, but were observed for different strains and temperatures. Size distribution for subgrains with boundary misorientations >2 degrees can be described as a bimodal lognormal area distribution. The distributions were found to change due to deformation. Part of the distribution describing the large subgrains decreased while the distribution for the small subgrains increased. This is in accordance with deformation being heterogeneous and successively spreading into the undeformed part of individual grains. The variation of the average size for the small subgrain distribution varies with strain but not with strain rate in the tested interval. The mean free distance for dislocation slip, interpreted here as the average size of the distribution of small subgrains, displays a variation with plastic strain which is in accordance with the different stages in the stress-strain curves. The rate of deformation hardening in the linear hardening range is accurately calculated using the variation of the small subgrain size with strain. (C) 2016 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license.
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| 36. |
- Yvell, Karin, et al.
(författare)
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Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation
- 2018
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 135:Supplement C, s. 228-237
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Tidskriftsartikel (refereegranskat)abstract
- Plastic deformation of surface grains has been observed by electron backscatter diffraction technique during in situ tensile testing of a high-nickel austenitic stainless steel. The evolution of low- and high-angle boundaries as well as the orientation changes within individual grains has been studied. The number of low-angle boundaries and their respective misorientation increases with increasing strain and some of them also evolve into high-angle boundaries leading to grain fragmentation. The annealing twin boundaries successively lose their integrity with increasing strain. The changes in individual grains are characterized by an increasing spread of orientations and by grains moving towards more stable orientations with 〈111〉 or 〈001〉 parallel to the tensile direction. No deformation twins were observed and deformation was assumed to be caused by dislocation slip only.
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