Composition Dependence of the Phase Stability in Au-Cd-Ag Martensitic Alloy☆

Abstract Au 52.5- x -Cd 47.5 -Ag x noble metal alloy undergoes martensitic transformation and shows complex Ag dependence on transformation temperature. As Ag composition ratio increases, β- and α- coexistence phase appears. The behavior of this Ag-rich region was studied. Atoms of the β-phase arrange disorderly (A2) in this region. The transformation temperature T 0 rises drastically and the magnitude of orthorhombic distortion becomes larger in comparison with that of adjoined β- single phase. This result suggests a correlation between the orthorhombic distortion and T 0 . Excessively high packing fraction of the α-phase, atomic disorder in the β-phase and small volume ratio of martensite / β-phase makes the β-phase unstable and stimulates transformation.