TEMPERATURE-DEPENDENCE OF THE 2ND-ORDER ELASTIC-CONSTANTS OF CU-ZN-ALSHAPE-MEMORY ALLOY IN ITS MARTENSITIC AND BETA-PHASE

The temperature dependence of the sound velocities for 13 propagation modes has been measured in a single crystal of Cu-Zn-Al monoclinic 18R martensite, using the pulse-echo method. By numerical procedure the c omplete set of nine second-order adiabatic elastic constants (C-ij) of the closest orthorhombic reference phase, their relative thermal vari ation (Gamma(ij)), and the Debye temperature (theta(D)) have been obta ined. The values found in the martensitic phase have been compared to data available for the high-temperature bcc beta-phase in the same all oy system. The velocity surfaces in the corresponding crystallographic directions of both phases have also been computed at different temper atures. It has been shown that the mechanical stability of the lattice for some particular distortions decreases as the transformation tempe rature is approached in both the martensitic as well as in the beta ph ase.