Reconciling Experimental and Theoretical Data in the Structural Analysis of Ti–Ta Shape-Memory Alloys
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The structural characterization of the various phases that occur in Ti–Ta-based high-temperature shape-memory alloys is complicated by the presence of many competing phases as a function of composition. In this study, we resolve apparent inconsistencies between experimental data and theoretical calculations by suggesting that phase separation and segregation of undesired phases are not negligible in these alloys, and that finite temperature effects should be taken into account in the modeling of these materials. Specifically, we propose that the formation of the ω phase at low Ta content and of the σ phase at high Ta content implies a difference between the nominal alloy composition and the actual composition of the martensitic and austenitic phases. In addition, we show that temperature affects strongly the calculated values of the order parameters of the martensitic transformation occurring in Ti–Ta.
KeywordsPhase separation Segregation High-temperature shape-memory alloys X-ray diffraction Density functional theory
This study has been supported by the Deutsche Forschungsgemeinschaft (DFG) within the research unit FOR 1766 (High Temperature Shape Memory Alloys, http://www.for1766.de, project number 200999873), as a collaboration between sub-projects TP1, TP2, and TP3. Part of the calculations have been carried out on the Gamma and Triolith clusters from the Swedish National Infrastructure for Computing (SNIC), and on the Beskow cluster from the Center for High Performance Computing (PDC).
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