Relation between long-range ordering and martensitic transformation temperature in Ag alloys

The relation between the degree of long-range order and the martensitic transformation temperature was examined by means of electrical resistivity measurements and electron microscopic observations in Ag–Zn–Al alloys having a composition near Ag2(Zn, Al). The disordered state of the β phase (bcc structure) can be frozen by quenching from a temperature above the critical temperature for ordering. By aging at or around the room temperature, atomic ordering is developed. The ordered structure after aging in the parent phase was found to be the C11b structure. Specimens in the disordered β phase transform to the martensitic phase on cooling below room temperature. It has been found that the martensitic transformation temperature is lowered by aging at temperatures between 253 and 293 K. This indicates that ordering brings about the decrease in the transformation temperature. The resistivity of the β phase measured at the aging temperature and that of the martensitic phase at liquid nitrogen temperature also decrease by aging. The resistivity change was related to the degree of long range order and the decrease in the transformation temperature was expressed as a function of the degree of order.