Electric resistivity anomaly and martensitic phase transformation in AuCuZn alloys

Abstract

The martensitic phase transformation in the beta-1 phase of Au-Cd alloys exhibits very complicated behaviours (1). In the case of Au-47.5 at % Cd alloy, for example, the electric resistivity of the slowly cooled beta-1 phase tends downward during the martensitic phase transformation while the reverse change occurs in the quenched one. When the quenched alloy is heated, the electric resistivity increases linearly and then its temperature gradient begins to decrease at about 385K. Above 420K, the electric resistivity rises again linearly with increasing temperature. Such a resistivity anomaly is an irreversible phenomenonon the thermal cycles. We confirm by the X-ray analysis that it is not concerned with any structural change. In the case of the slowly cooled alloy, on the other hand, the resistivity anomaly does not occur. We conclude that the resistivity anomaly is originated from the annihilation of quenched-in vacancies introduced into the beta-1 phase.