The Thermal Effect in Pseudoelastic Single Crystals of β-CuZnSn

Abstract

The thermal effect associated with the formation and reversion of stress-inducedβ2 martensite has been studied in single crystals of β2-CuZnSn. The martensite in this system forms as isolated plates of β2 which increase in number and ultimately coalesce. The maximum temperature pulse obtained increased with fraction of specimen undergoing transformation and reached a maximum for complete transformation. The temperature pulse was the same for the forward and reverse transformations and the same at different points on the specimen. The maximum temperature change increased with increasing strain rate and reached a constant at high strain rates. Calculations showed that heat loss to an air environment was negligible at high strain rates and the transformation could be considered adiabatic. In tests in water there was always a significant heat loss to the environment and corrections were necessary to allow for this. The temperature rise under adiabatic conditions was used to calculate the entropy change of the transformation and gave ΔSβ2 - β2 = - 1.03 ± 0.07 J/mol K, in excellent agreement with tke value of - 1.00 ± 0.17 J/mol K found from the Clausius-Clapeyron equation. The variation of the entropy change with specimen temperature was small and could be considered constant within experimental error.