| 1. |
- Mukhamedov, Boburjon, et al.
(author)
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Tetragonal distortion in magnetron sputtered bcc-W films with supersaturated carbon
- 2022
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In: Materials & design. - : Elsevier Science Ltd. - 0264-1275 .- 1873-4197. ; 214
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Journal article (peer-reviewed)abstract
- Carbon has a low solid solubility in bcc tungsten at equilibrium. However, metastable supersaturated solid solutions can be synthesized with magnetron sputtering. Here, we present a systematic study on the phase stability and mechanical properties of such supersaturated W-C solid solutions. H-2h scans show a split of the 200/020 and the 002 peaks for supersaturated films which is explained by a tetragonal distortion of the bcc structure. This split increases with increasing C content and is maximized at 4 at.% C, where we observe an a/b axis of 3.15-3.16 A and a c-axis of 3.21-3.22 A. We performed first-principles calculations of lattice parameters, mixing enthalpies, elastic constants and polycrystalline elastic moduli for cubic and tetragonal W-C solid solutions. Calculations show that tetragonal structure is more stable than the bcc supersaturated solid solution and the calculated lattice parameters and Youngs moduli follow the same trends as the experimental ones as a function of C concentration. The results suggest that supersaturated films with lattice distortion can be used as a design approach to improve the properties of transition metal films with a bcc structure. (c) 2022 The Authors. Published by Elsevier Ltd.
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| 2. |
- Osinger, Barbara, et al.
(author)
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Investigation of the phase formation in magnetron sputtered hard multicomponent (HfNbTiVZr)C coatings
- 2022
-
In: Materials & design. - : ELSEVIER SCI LTD. - 0264-1275 .- 1873-4197. ; 221
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Journal article (peer-reviewed)abstract
- Multicomponent carbides have gained interest especially for ultra-high temperature applications, due to their ceramic hardness, good oxidation resistance and enhanced strength. In this study the phase forma-tion, stability and mechanical properties of (HfNbTiVZr)C multicomponent carbide coatings were inves-tigated. Phase stability was predicted by the CALPHAD (CALculation of PHAse Diagrams) methods. This revealed that the multicomponent solid solution phase is only stable at elevated temperatures, namely above 2400 degrees C. At lower temperatures a phase mixture was predicted, with a particular tendency for V to segregate. Magnetron sputtered thin films deposited at 300 degrees C exhibited a single NaCl-type multicom-ponent carbide phase, which attributes to the kinetic stabilisation of simple structures during thin film growth. Films deposited at 700 degrees C, or exposed to UHV annealing at 1000 degrees C, however, revealed the decom-position of the single-phase multicomponent carbide by partial elemental segregation and formation of additional phases. Thus, confirming the CALPHAD predictions. These results underscore the importance of explicitly considering temperature when discussing the stability of multicomponent carbide materials, as well as the applicability of CALPHAD methods for predicting phase formation and driving forces in these materials. The latter being crucial for designing materials, such as carbides, that are used in appli-cations at elevated temperatures.
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