MECHANICAL ANISOTROPY ASSOCIATED WITH THE BETA(2)-]ZETA'(2) MARTENSITIC-TRANSFORMATION IN AUCD SHAPE-MEMORY ALLOYS

Applying stress to shape memory alloy (SMA) single crystals in the sup erelastic temperature regime induces reversible strain associated with transformation from austenite to martensite. The phenomenological the ory of martensite crystallography predicts a reversible transformation strain for SMAs, which can be closely approximated by a set of shear vector-shear plane combinations. Since the transformation shear system s have particular orientations relative to the austenite crystal, it i s expected that the stress required for transformation, and the result ing transformation strain, will be anisotropic. A correlation has rece ntly been proposed between the shear vector-shear plane orientations a nd mechanical anisotropy of SMA single crystals. The present paper mod els the beta(2)-to-zeta(2)(') (trigonal) martensitic transformation in AuCd with the objective of testing the proposed correlation. The tran sformation shear systems in AuCd approximate (110){0(1) over bar1$}(be ta 2) shear systems, which the correlation suggests should result in s trong mechanical anisotropy. The model results for AuCd exhibit strong anisotropy, consistent with the previously proposed correlation.