Effect of aging on the martensitic transformation temperature in Ag-Zn-Al alloys

The relation between atomic ordering and martensitic transformation temperature, M-s, in Ag-Zn-Al alloys was examined mainly by means of electrical resistivity measurements. Disordered bcc phase was frozen-in by quenching from a temperature above the critical temperature for ordering, T-c. In a Ag-22.3at%Zn-8.9at%Al alloy, the M-s temperature has been found to decrease by aging in the parent phase at temperatures between 253 and 293K. The resistivity also decreased in accord with the M-s temperature. This indicates that atomic ordering proceeds by aging, The relation between the decrease in the reverse transformation temperature, A(f), and the degree of long range order was obtained. In a Ag-11.0at%Zn-15.5at%Al alloy, in which the M-s temperature in the as-quenched state is higher and the T-c temperature is lower than that of the former alloy, aging in the martensite phase was performed, In this case, the aging brought about the increase in the A(f) temperature. This is in contrast to the results of aging in the parent phase. Furthermore, the effect of aging in the parent phase at temperatures higher than T-c was examined. Both the transformation temperature and the resistivity were found to become higher. These changes are due to lowering in the degree of short range order.