| 1. |
- Bylin, Johan, et al.
(author)
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Hydrogen-induced volume changes, dipole tensor, and elastic hydrogen-hydrogen interaction in a metallic glass
- 2022
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:10
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Journal article (peer-reviewed)abstract
- Hydrogen and its isotopes, absorbed in metals, induce local stress on the atomic structure, which generates a global expansion in proportion to the concentration of hydrogen. The dipole force tensor and its interaction with the stress fields give rise to an effective attractive nonlocal potential between hydrogen atoms-the elastic hydrogen-hydrogen interaction-which is a key quantity governing the phase transitions of hydrogen in metals. While the dipole tensor and the elastic interaction have been researched in crystalline materials, they remain experimentally unexplored in metallic glasses and it is unclear how these quantities are affected by the lack of point group symmetries. Here, we investigate both experimentally and theoretically the volume changes, the components of the force dipole tensor, and ultimately the elastic hydrogen-hydrogen interaction in the metallic glass V80Zr20. In situ neutron reflectometry was used to determine the deuterium-induced volume changes as a function of deuterium concentration. The one-dimensional volume expansion is found to change by more than 14% without any structural degradation, up to concentrations of one deuterium atom per metal atom. From the expansion, we determine that the out-of-plane component of the elastic dipole tensor is remarkably similar to a composition weighted sum of the ones found in crystalline vanadium and zirconium. Via ab initio calculations of both free and biaxially constrained expanded metallic structures, we determine that the trace of the dipole tensor varies with hydrogen concentration and is essentially invariant of global elastic boundary conditions. As a consequence, the elastic hydrogen-hydrogen interaction energy is found to be concentration-dependent as well, illustrating that the disordered nature of a metallic glass does not impede the mediation of the elastic attraction, but rather allows it to vary with hydrogen content.
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| 2. |
- Folkenant, Matilda, et al.
(author)
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Structure and properties of Cr–C/Ag films deposited by magnetron sputtering
- 2015
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In: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 281, s. 184-192
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Journal article (peer-reviewed)abstract
- Cr–C/Ag thin films with 0–14 at.% Ag have been deposited by magnetron sputtering from elemental targets. The samples were analyzed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to study their structure and chemical bonding. A complex nanocomposite structure consisting of three phases; nanocrystalline Ag, amorphous CrCx and amorphous carbon is reported. The carbon content in the amorphous carbide phase was determined to be 32–33 at.% C, independent of Ag content. Furthermore, SEM and XPS results showed higher amounts of Ag on the surface compared to the bulk. The hardness and Young's modulus were reduced from 12 to 8 GPa and from 270 to 170 GPa, respectively, with increasing Ag content. The contact resistance was found to decrease with Ag addition, with the most Ag rich sample approaching the values of an Ag reference sample. Initial tribological tests gave friction coefficients in the range of 0.3 to 0.5, with no clear trends. Annealing tests show that the material is stable after annealing at 500 °C for 1 h, but not after annealing at 800 °C for 1 h. In combination, these results suggest that sputtered Cr–C/Ag films could be potentially applicable for electric contact applications.
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| 3. |
- Fritze, Stefan, et al.
(author)
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Hard and crack resistant carbon supersaturated refractory nanostructured multicomponent coatings
- 2018
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In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 8
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Journal article (peer-reviewed)abstract
- The combination of ceramic hardness with high crack resistance is a major challenge in the design of protective thin films. High entropy alloys have shown in earlier studies promising mechanical properties with a potential use as thin film materials. In this study, we show that small amounts of carbon in magnetron-sputtered multicomponent CrNbTaTiW films can lead to a significant increase in hardness. The film properties were strongly dependent on the metal composition and the most promising results were observed for TaW-rich films. They crystallised in a bcc structure with a strong (110) texture and coherent grain boundaries. It was possible to deposit films with 8 at.% C in a supersaturated solid-solution into the bcc structure without carbide formation. A major effect of carbon was a significant grain refinement, reducing the column diameter from approximately 35 to 10 nm. This resulted in an increase in hardness from 14.7 to 19.1 GPa while the reduced E-modulus stayed constant at 322 GPa. The carbon-containing films exhibited extremely little plastic deformation around the indent and no cracks were observed. These results show that supersaturation of carbon into high entropy films can be a promising concept to combine superior hardness with high crack resistance.
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| 4. |
- Fritze, Stefan, et al.
(author)
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Influence of Deposition Temperature on the Phase Evolution of HfNbTiVZr High-Entropy Thin Films
- 2019
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In: Materials. - : MDPI. - 1996-1944. ; 12:4
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Journal article (peer-reviewed)abstract
- In this study, we show that the phase formation of HfNbTiVZr high-entropy thin films is strongly influenced by the substrate temperature. Films deposited at room temperature exhibit an amorphous microstructure and are 6.5 GPa hard. With increasing substrate temperature (room temperature to 275 degrees C), a transition from an amorphous to a single-phased body-centred cubic (bcc) solid solution occurs, resulting in a hardness increase to 7.9 GPa. A higher deposition temperature (450 degrees C) leads to the formation of C14 or C15 Laves phase precipitates in the bcc matrix and a further enhancement of mechanical properties with a peak hardness value of 9.2 GPa. These results also show that thin films follow different phase formation pathways compared to HfNbTiVZr bulk alloys.
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| 5. |
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| 6. |
- Kaplan, Maciej, 1991-, et al.
(author)
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Hydrogen-induced enhancement of thermal stability in VZr(H) metallic glasses
- 2022
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In: Materialia. - : Elsevier BV. - 2589-1529. ; 24
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Journal article (peer-reviewed)abstract
- Prediction of crystallization temperatures in metallic glasses is still an open question. Investigations of multi component alloys are common in the literature, however, binary and ternary alloys are more suitable for funda-mental studies due to their simplicity. Here, we show that a low thermodynamic driving force for crystallization can be associated with a high crystallization temperature. The driving force is determined by calculating - for the first time in metallic glasses - the temperature dependent Gibbs free energies of the alloys using ab initio density functional theory, in combination with the stochastic quenching method. The crystallization tempera-tures of VxZr100-x and VxZr67-xH33 have been determined using simultaneous in-situ x-ray scattering techniques and resistivity measurements. The onset of crystallization is found to exhibit a parabolic dependence throughout the composition range, whereas alloying with hydrogen increases the thermal stability up to 150 K close to the amorphous-crystalline boundaries. These findings suggest that hydrogen acts as an alloying element with the ability to dynamically tune the intrinsic properties of the material. Lastly, temperature-dependent descriptions of the Gibbs free energy and kinetic considerations of a metallic glass are necessary for a complete characterization of the crystallization process.
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| 7. |
- Komander, Kristina, et al.
(author)
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Accurate measurement of hydrogen concentration in transition metal hydrides utilizing electronic excitations by MeV ions
- 2024
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In: International journal of hydrogen energy. - : Elsevier. - 0360-3199 .- 1879-3487. ; 57, s. 583-588
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Journal article (peer-reviewed)abstract
- This study focuses on enhancing the accuracy of hydrogen content verification in hydrogen-rich ultrathin materials relevant for sustainable energy applications. Ion beams are used for distinctive real-space detection leveraging elastic and inelastic interactions with hydrogen atoms. However, the lack of experimental reference data on electronic interactions poses a challenge to the accuracy of analytical techniques. We investigate the effect of absorbed hydrogen on the electronic energy deposition of 15N-ions in amorphous transition metal compounds, specifically V and Zr, covering concentrations >1H/M. Employing resonant nuclear reactions and Rutherford backscattering, the energy loss is found to increase considerably with hydrogen content, in line with Bragg's additivity. The electronic energy loss cross section for 15N-ions at 6.5 MeV measured (64.55±3.38) eV cm2/1015 atoms. Results are compared to semi-empirical and theoretical models. The findings improve hydrogen profiling accuracy using 15N-nuclear reaction analysis and enable unprecedented methods for hydrogen quantification by other, commonly available ion beams.
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| 8. |
- Malinovskis, Paulius
(author)
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Magnetron sputtering of binary, ternary and multicomponent thin film borides and carbides
- 2018
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Doctoral thesis (other academic/artistic)abstract
- Design of new thin film materials with improved properties and functionality is an important research field in materials science. In this thesis, I have used magnetron sputtering to deposit new thin film materials, which should combine high hardness and high ductility with other properties such as low friction or a good corrosion resistance. The films have been characterized with a range of techniques to determine the correlation between deposition parameters, microstructure and properties. The first part of the thesis is focussed on binary and ternary molybdenum-containing boride thin films with potential low-friction properties. It was found that the binary Mo-B films exhibited a nanocrystalline structure of ~ 16 nm large MoB2-x grains surrounded by an amorphous tissue phase. The special microstructure resulted in a very high hardness (29 ± 2 GPa), but limited ductility. An attempt to improve the ductility by formation of crystalline layered ternary borides such as Mo2BC and Mo2FeB2 failed due to difficulties to reach high deposition temperatures. However, the addition of carbon to the binary Mo-B films resulted initially in a reduced grain size of the MoB2-x grains. For carbon concentrations >23 at.%, a completely amorphous film was formed. Transmission electron microscopy (TEM) studies revealed that these films contained Mo-rich regions surrounded by a Mo-poor amorphous BCx phase and therefore best can be described an amorphous nanocomposite. The mechanical properties of the Mo-B-C films were strongly correlated to the amount of the softer amorphous BCx phase. Also the Mo-Fe-B films were amorphous with a hardness ranging from 19 to 26 GPa and a limited ductility. Tribological studies of the Mo-B, Mo-B-C and Mo-Fe-B films showed very high coefficients of friction (>0.8). Molybdenum and boron oxides were identified on the surface by Raman spectroscopy, but no indication of lubricating effects from these oxides could be observed. The results suggest that Mo-based borides have limited applications in future low-friction applications.In the second part of the thesis, a high entropy alloy (HEA) of TiCrNbTaW was studied with and without the addition of carbon. The results showed that a HEA phase with bcc structure could be deposited in a wide composition and temperature range. Small amounts of carbon were dissolved into the bcc phase, while higher carbon contents resulted in a multicomponent carbide phase. The correlation between structure and properties were studied in detail. It was found that some of the films exhibited very high hardness combined with high ductility suggesting potential application of these materials as wear-resistant coatings. Finally, the corrosion resistance of these complex alloys were investigated in a very acidic environment. They were found to exhibit excellent corrosion resistance superior to hyper-duplex stainless steels.
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| 9. |
- Malinovskis, Paulius, et al.
(author)
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Synthesis and characterisation of Mo-B-C thin films deposited by non-reactive DC magnetron sputtering
- 2017
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 309, s. 506-515
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Journal article (peer-reviewed)abstract
- Thin films in the Mo-B-C system with varying carbon content (up to 37 at.%) were deposited using non-reactive DC magnetron sputtering. The phase composition and microstructure were determined and the potential use of the films in sliding electrical contact applications was evaluated. Films with lower than 23 at.% carbon content consisted of nanocrystalline MoB2 - x grains surrounded by an amorphous tissue phase (a-B for binary, and a-BCx for ternary films). With increasing carbon content grain sizes was found to decrease (from 16 to 5 nm), and above 23 at.% carbon the films deposited at room temperature were X-ray amorphous. Scanning transmission electron microscopy and energy dispersive X-ray spectroscopy reveal that these films contain Mo-rich and Mo-poor regions, and thus are two-phase amorphous nanocomposites. Low-carbon content samples exhibited a friction coefficient against the steel counter surface of 1.1; this was reduced to 0.8 for high carbon-content films. Analysis of the tribofilm revealed formation of molybdenum oxide and amorphous carbon, however without significant lubricating effect at room temperature. Hardness and elastic modulus decrease with carbon content from similar to 29 to similar to 22 GPa and similar to 526 to similar to 326 GPa. These values give an WE ratio of 0.06 to 0.07, indicating brittle material. Resistivity was found to increase with carbon content from similar to 175 mu Omega cm for binary Mo-B to similar to 395 mu Omega cm for Mo-B-C thin film with 37 at.% of C. Therefore all the above results suggest that the Mo-B-C films are not suitable for sliding electrical contacts.
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| 10. |
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| 11. |
- Malinovskis, Paulius, et al.
(author)
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Synthesis and Characterisation of Nanocomposite Mo-Fe-B Thin Films Deposited by Magnetron Sputtering
- 2021
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In: Materials. - : MDPI. - 1996-1944. ; 14:7
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Journal article (peer-reviewed)abstract
- Several ternary phases are known in the Mo-Fe-B system. Previous ab initio calculations have predicted that they should exhibit a tempting mix of mechanical and magnetic properties. In this study, we have deposited Mo-Fe-B films with a Fe-content varying from 0-37 at.% using non-reactive DC (direct current) magnetron sputtering. The phase composition, microstructure, and mechanical properties were investigated using X-ray diffraction, scanning transmission electron microscopy, and nanoindentation measurements. Films deposited at 300 degrees C and with >7 at.% Fe are nanocomposites consisting of two amorphous phases: a metal-rich phase and a metal-deficient phase. Hardness and elastic modulus were reduced with increasing Fe-content from similar to 29 to similar to 19 GPa and similar to 526 to similar to 353 GPa, respectively. These values result in H-3/E-2 ratios of 0.089-0.052 GPa, thereby indicating brittle behaviour of the films. Also, no indication of crystalline ternary phases was observed at temperatures up to 600 degrees C, suggesting that higher temperatures are required for such films to form.
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| 12. |
- Malinovskis, Paulius, et al.
(author)
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Synthesis and characterization of MoB2-x thin films grown by nonreactive DC magnetron sputtering
- 2016
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 34, s. 031511-1-031511-8
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Journal article (peer-reviewed)abstract
- DC magnetron sputtering was used to depositmolybdenumboridethin films for potential low-friction applications. The films exhibit a nanocomposite structure with ∼10 nm large MoB2−x (x > 0.4) grains surrounded by a boron-rich tissue phase. The preferred formation of the metastable and substoichiometric hP3-MoB2structure (AlB2-type) is explained with kinetic constraints to form the thermodynamically stable hR18-MoB2 phase with a very complex crystal structure. Nanoindentation revealed a relatively high hardness of (29 ± 2) GPa, which is higher than bulk samples. The high hardness can be explained by a hardening effect associated with the nanocomposite microstructure where the surrounding tissue phase restricts dislocation movement. A tribological study confirmed a significant formation of a tribofilm consisting of molybdenum oxide and boron oxide, however, without any lubricating effects at room temperature.
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| 13. |
- Malinovskis, Paulius, et al.
(author)
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Synthesis and characterization of multicomponent (CrNbTaTiW)C films for increased hardness and corrosion resistance
- 2018
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In: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 149, s. 51-62
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Journal article (peer-reviewed)abstract
- Multicomponent carbide thin films of (CrNbTaTiW)C (30–40 at.% C) with different metal contents were depos-ited at different temperatures using non-reactive DC magnetron sputtering. The lattice distortion for the metallattice was estimated to vary from about 3 to 5%. Most films crystallized in the cubic B1 structure but Ta/W-rich films deposited at 600 °C exhibited a tetra gonal distortion. X-ray diffraction results sh ow that near-equimolar films exhibited a strong (111) texture. In contrast, Ta/W-rich films exhibited a shift from (111) to(100) texture at 450 °C. The in-plane relationship was determined to MC(111)[-12-1]//Al2O3(001)[110] with alattice mismatch of about 11% along the Al2O3[110] direction. A segregation of Cr to the grain boundaries was ob-served in all films. The microstructure was found to be the most important factor for high hardness. Less denseNb-rich and near-equimolar films deposited at low tem peratures exhib ited the low est hardnes s (12 GPa),while very dense Ta/W-rich high temperature films were found to be the hardest (36 GPa). No correlation wasfound between the lattice distortion and the hardness. Corrosion studies revealed that the multicomponentfilms exhibited excellent corrosion resistance, superior to that of a reference hyper-duplex stainless steel, in1.0 M HCl.
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| 14. |
- Meng, Qingnan, et al.
(author)
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Characterization of amorphous Zr-Si-C thin films deposited by DC magnetron sputtering
- 2015
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In: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 261, s. 227-234
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Journal article (peer-reviewed)abstract
- Zr-x(SiyC1-y)(1-x) films with different Si/C atomic ratios and Zr contents were deposited using non-reactive dc-magnetron co-sputtering. All films exhibited an X-ray amorphous structure with a complex distribution of chemical bonds. The presence of Zr in the films reduced the amount of C-C and Si-C bonds but favored the formation of Zr-C and Zr-Si bonds. The mechanical and electrical properties were dependent on the bond distribution in the amorphous structure and a linear relationship between film hardness and the relative amount of Si-C bonds was observed. The addition of Zr in films also gave rise to an increase in metallic character resulting in a lower electrical resistivity. Analysis of the tribofilm showed that a low friction coefficient was favored by the formation of a lubricating a-C layer and that the formation of zirconium and silicon oxides in the more Zr-rich films has a detrimental effect on the tribological performance. (C) 2014 Elsevier B.V. All rights reserved.
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| 15. |
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| 16. |
- Shinde, Deodatta, 1985, et al.
(author)
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Elemental Distribution in CrNbTaTiW-C High Entropy Alloy Thin Films
- 2019
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In: Microscopy and Microanalysis. - : CAMBRIDGE UNIV PRESS. - 1435-8115 .- 1431-9276. ; 25:2, s. 489-500
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Journal article (peer-reviewed)abstract
- The microstructure and distribution of the elements have been studied in thin films of a near-equimolar CrNbTaTiW high entropy alloy (HEA) and films with 8 at.% carbon added to the alloy. The films were deposited by magnetron sputtering at 300°C. X-ray diffraction shows that the near-equimolar metallic film crystallizes in a single-phase body centered cubic (bcc) structure with a strong (110) texture. However, more detailed analyses with transmission electron microscopy (TEM) and atom probe tomography (APT) show a strong segregation of Ti to the grain boundaries forming a very thin Ti-Cr rich interfacial layer. The effect can be explained by the large negative formation enthalpy of Ti-Cr compounds and shows that CrNbTaTiW is not a true HEA at lower temperatures. The addition of 8 at.% carbon leads to the formation of an amorphous structure, which can be explained by the limited solubility of carbon in bcc alloys. TEM energy-dispersive X-ray spectroscopy indicated that all metallic elements are randomly distributed in the film. The APT investigation, however, revealed that carbide-like clusters are present in the amorphous film.
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| 17. |
- Srinath, Aishwarya, 1991-, et al.
(author)
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An investigation of the corrosion resistances of magnetron sputtered TaW-rich, Nb-rich, and multicomponent CrNbTaTiW alloys
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Other publication (other academic/artistic)abstract
- The corrosion resistances of magnetron sputtered nearequimolar, TaW-rich, and Nb-rich CrNbTiTaW alloys, with and without 8 at.% carbon, were studied in aqueous chloride-containing environments. Electrochemical tests and scanning electron images showed that all the CrNbTaTiW alloys were highly corrosion resistant in 1.0 M HCl. The results conclusively showed that passivated nearequimolar CrNbTaTiW coatings have comparable corrosion performances to passivated Nb- and TaW-rich alloys in 0.01 M HCl + 0.1 M NaCl. Carbon affected the rate of surface repassivation in polarisation measurements of the films whose oxide had been partially reduced, but had a minor influenceon the corrosion resistances once a mature oxide was formed. No conclusive relationships between microstructure and corrosion resistance were established. The comparable corrosion resistances of the multicomponent CrNbTiTaW, Nb-rich and TaW-rich alloys were attributed to the presence of extremely stable surface oxides of Nb and Ta which prevented losses of Ti and Cr. The near surface regions of all the alloys before and after corrosion appeared to be depleted in W compared to the bulk.
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| 18. |
- Vasiliauskas, Remigijus, et al.
(author)
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Polytype Inclusions in Cubic Silicon Carbide
- 2013
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In: Silicon Carbide and Related Materials 2012. - : Trans Tech Publications. - 9783037856246 ; , s. 335-338
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Conference paper (peer-reviewed)abstract
- In this paper, we review our research on 6H-SiC polytype inclusions in 3C-SiC layers, which were grown on nominally on-axis 6H-SiC substrates using sublimation epitaxy. More than 90% coverage by 3C-SiC is typically achieved at growth temperature of 1775 degrees C. The main reason for the polytype inclusions to appear is local supersaturation non-uniformities over the sample surface which appear due to the temperature gradient and spiral growth nature of 6H-SiC. On the 6H-SiC spirals with small steps supersaturation is smaller and 3C-SiC nucleation and growth is diminished. Due to surface free energy and surface diffusion differences, polytype inclusions appear differently when 3C-SiC is grown on the Si- and C-faces. The 6H-SiC inclusions as well as twin boundaries act as neutral scattering centers and lower charge carrier mobility
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