Interface characteristics and tensile fracture behavior of CoCrFeNi/6061Al matrix composites fabricated via spark plasma sintering and heat treatment

Abstract

In this study, 3vol%CoCrFeNi high-entropy alloy (HEA) reinforced 6061Al matrix composites were prepared using spark plasma sintering (SPS), and a new strategy to regulate the interfacial structure of the diffusion layer by solid solution heat treatment was proposed. Based on the thermodynamics and kinetics of solid-state diffusion, the mechanism of the formation and growth of the diffusion layer and its influence on the mechanical properties of the composites were analyzed. At a solid solution temperature of 535 °C, a uniform diffusion layer forms between HEA and Al matrix, and the thickness of the diffusion layer increases with the extension of solid solution time. The diffusion layer is determined as a two-layer structure, with a columnar solid solution grain near HEA and an equiaxed crystal along with Al9Co2 solid solution layer near Al matrix. Optimal tensile strength and elongation of 211.5 MPa and 21.4% respectively are obtained at solid solution time of 60 min, with 12.8 μm in thickness. Superior interface bonding resulting from diffusion layer prevents the crack from expanding into the matrix, contributing to an enhanced ductility with the extension of solid solution time. This study provides valuable insights and theoretical guidance for developing HEA/Al composites with superior strength-ductility synergy.