Critical Temperature for Ordering and B2 Domain Structure in Ag–Zn β Phase Alloys

Abstract

The critical temperature for the order-disorder transition, T c , and the ordered domain structure of the B2 phase have been investigated by electrical resistivity measurements and electron microscopic observations in Ag-Zn alloys containing 38, 40 and 42 at%Zn. Specimens quenched from the disordered β phase were all found to be ordered in the B2 structure. Resistivity change measured during aging of the B2 phase shows a plateau at the initial stage of aging. This indicates the degree of order reaches the equilibrium value immediately after the start of aging. The B2 domain size as measured after aging and quenching increases as the aging temperature increases. However, it takes a smaller value when the aging temperature is beyond T c . Values of T c were determined by monitoring the domain size as 441, 405 and 367 K for the 42, 40 and 38Zn alloys, respectively. The ragging or fluctuating of anti-phase domain boundaries was recognized in the specimens aged at a temperature just below T c . The activation energy for the domain growth was obtained by measuring growth rates as 49.3 kJ/mol, which was judged to correspond to the migration energy of excess vacancies.