Elastic constant softening and martensite nucleation in a CuZnAl single crystal

The ultrasonic attenuation A and the elastic constants C-44, C-1 and C' hav e been measured during thermal cycles carried out above the martensite star t-temperature M-s (M-s = 267 K) in a single crystal of the Cu67.93Zn19.03Al 13.04 alloy. The ultrasonic attenuation displays a sharp maximum at a tempe rature which is about 6 degrees higher than M-s. This temperature differenc e can be accounted for either in terms of the Clausius-Clapeyron law for th e martensite induced by the applied ultrasonic stress-held or in terms of p remartensitic effects. Thermal hysteresis occurs for all the elastic consta nts C-44, C-1 and C' and the data are consistent with those previously obta ined for the Young's modulus in a polycrystalline alloy of the same system. The thermal hysteresis is attributed to the formation of stable nuclei of martensite at strong defects. (C) 2000 Elsevier Science S.A. All rights res erved.