Phase Relation and Kinetics of the Transformations in Au-Cu-Zn Ternary Alloys

Abstract

The phase relation in the β phase Au _x Cu_55-x Zn₄₅ ternary alloys was studied. There appear two types of ordered phases, i.e., the Heusler-type and the CsCl-type superlattices, and a martensite structure at low temperatures. The critical temperature (T _c ) of CsCl-type superlattice becomes higher than that (455°C) of the Cu-Zn binary alloy with the increase in Au content. T _c of the Heusler-type has a maximum (390°C) near the stoichiometric composition of AuCuZn₂. The martensitic transformation temperature (T ₀) increases up to a maximum (45°C) at the 26 at.% Au and then decreases with the further increase in Au content. The nature of the stability of the β phase was discussed from the view point of ionic radii of the constituent elements, electron atom ratio and quenched-in vacancies.