Energy barriers and hysteresis in martensitic phase transformations
by
Zhiyong Zhang, R. D. James and Stefan Mueller
in
Acta Materialia (overview), , 2009.
Category: Preprint
Keywords: NiTi, Hysteresis, Twinning, TEM, Compatibility, habit plane, interfaces
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Abstract:
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 identi ed previously with low hysteresis. We achieve 2 = 1, where 2 is the middle eigenvalue of the transformation stretch 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 2 = 1. When the size of the hysteresis is replotted vs. 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.
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