Just another WordPress site - Ruhr-Universität Bochum

Abstract

High-temperature shape memory alloys have applications in the automotive, aviation and biomedical sectors. The martensitic transformation temperature (M_s) and mechanical properties of these materials often exhibit a strong dependence on the chemical composition. Insight into the underlying mechanisms and phase stability of the competing austenite and martensite phases can help to device new alloys with the desired functional properties at elevated temperatures. The free energy is a key quantity for determining the composition dependent transformation temperature between the involved crystal phases. We approximate the different contributions to the free energy as a function of composition based on density functional theory calculations and compare the stability of competing phases at finite temperature. In addition to the thermodynamic phase stability we investigate the mobility of the different elements within the alloy which is key to analyze segregation and redistribution at elevated temperatures. We find that the 0K energy difference and the Debye temperature difference between the involved phases are the critical parameters for predicting the composition dependence of M_s. From our calculations we identify a one dimensional descriptor for estimating M_s that may be used in high-throughput screening of ternary or multicomponent alloys for a computationally guided development of novel high-temperature shape memory alloys.