Two types of checkerboard-like microstructures in Au–Cu–Pd ternary alloys

Abstract The phase transformation process in Au–Cu–Pd ternary alloys with the compositions within or near the two-phase region (Au 3 Cu+AuCu I) was studied by means of transmission electron microscopy and hardness testing. Two types of characteristic checkerboard-like microstructures were observed: (1) the coexistence of the Au 3 Cu and AuCu I ordered phases, and (2) the coexistence of the AuCu I ordered phase and disordered phase with face-centered cubic structure. Different age-hardening behaviors were recognized: The high hardness value in the former was maintained for prolonged aging periods, and that produced in the latter was maintained to a certain period followed by over-aging.