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Energy barriers and hysteresis in martensitic phase transformations
Zhiyong Zhang, Richard D. James and Stefan Müller
We report results from a systematic program of alloy development in the system TiNiX, X$ = $ Cu, Pt, Pd, Au, to pursue certain special lattice parameters that have been identified previously with low hysteresis. We achieve $\lambda_2 = 1$, where $\lambda_2$ is the middle eigenvalue of the transformation strain matrix, for alloys with X = Pt, Pd, Au. In all cases there is a sharp drop of the graph of hysteresis vs. composition at the composition where $\lambda_2 = 1$. When the size of the hysteresis is replotted vs. $\lambda_2$ we obtain a universal graph for these alloys.
Motivated by these experimental results, we present a new theory for the size of the hysteresis based on the growth from a small scale of fully developed austenite martensite needles. The energy of the transition layer plays a critical role in this theory. Overall, the results point to a simple systematic method of achieving low hysteresis and a high degree of reversibility in transforming materials.