Ordering and phase separation in the ternary Ag-Cu-Zn β-phase alloys

Abstract

The microstructure of the ternary Ag x Cu 55− x Zn 45 and Ag x Cu 53− x Zn 47 β-phase alloys was studied by means of electron microscopy. The range of temperature and composition where the mottled and modulated structures appeared was investigated, and the composition dependence of the spinodal decomposition temperature T s was also estimated. The composition dependence of T s had a maximum at about Ag 22 at.%. The critical temperature of the CsCl(B2)-type superstructure T c decreased with increase in Ag content, but was constant in a range of composition where the phase separation was observed. The precipitation of α-phase (f.c.c.) was observed even in the quenched specimens, that suggests the phase separation of β-phase at a high temperature. The composition dependence of T c and T s , was calculated theoretically. The occurrence of the ordering and the spinodal decomposition in the ternary Ag-Cu-Zn β-phase alloys is discussed briefly in terms of the difference of ordering energy that is negative in Ag-Zn and Cu-Zn pairs and positive in Ag-Cu pair.