Grain interior precipitation and related lamellar forming grain boundary reaction in Ag–Pd–Cu–Au–Zn alloy

Abstract

Grain interior precipitation and related lamellar forming grain boundary reaction in an Ag–Pd–Cu–Au–Zn alloy were examined by characterising the hardening behaviour, phase transformations, changes in microstructure and changes in element distribution during aging. The solution treated specimen was composed of the Ag–Au rich α1 matrix and the CuPd β1 particle-like structures of various sizes containing Zn. The α1 phase decomposition into α2 and α3 in the grain interior accompanied the microstructural changes into fine tweed-like structure containing lattice strains in the interphase boundaries, resulting in hardening in the early stage of aging process. The increased lattice strains in the grain interior induced the grain boundary reaction, stimulating the development of coarse lamellar structure composed of the α2 and α3 phases. The increase in volume fraction of the lamellar structure accompanied the decrease in hardness by consuming the dense interphase boundaries of the fine tweed-like structure.