Elastic constant softening and martensite nucleation in a CuZnAl single crystal

Abstract

The ultrasonic attenuation A and the elastic constants C 44, C L and C′ have been measured during thermal cycles carried out above the martensite start-temperature M s ( M s =267 K) in a single crystal of the Cu 67.93Zn 19.03Al 13.04 alloy. The ultrasonic attenuation displays a sharp maximum at a temperature which is about 6 degrees higher than M s . This temperature difference can be accounted for either in terms of the Clausius–Clapeyron law for the martensite induced by the applied ultrasonic stress-field or in terms of premartensitic effects. Thermal hysteresis occurs for all the elastic constants C 44, C L and C′ and the data are consistent with those previously obtained 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.