A study on the effect of Cr content on the microstructure and nanohardness of (CoFeNi)100-xCrx high entropy alloys by diffusion couple method

Abstract

A high-throughput experimental method combining diffusion couple and nanoindentation technique provides a high-efficiency way to obtain the influence of Cr content on the microstructure and micromechanical properties of the (CoFeNi)_100-xCr_x high entropy alloys (HEAs). In the present work, the microstructural evolution of CoFeNi-(CoFeNi)₅₅Cr₄₅ diffusion couple after annealing at 800 °C, 1000 °C, and 1200 °C has been investigated. The phase constitution of the diffusion couple is fcc + bcc two-phase at 1200 °C, while fcc+σ two-phase forms at 800 °C and 1000 °C. As the annealing temperature increases, the interdiffusion zone (IDZ) and the phase-boundary movement distance (PBMD) at the interface of diffusion couple specimen expands, with the IDZ and the PBMD reaching 500 μm and 170 μm, respectively, at 1200 °C. Furthermore, the nanohardness in IDZ increases with the Cr content, which is mainly due to the significant lattice distortion effect caused by Cr addition. The CALculated PHAse Diagram (CALPHAD) method was used to simulate the phase evolution and phase boundary movement of the diffusion couple specimens. In turn, the microstructural evolution of the diffusion couple specimen at different annealing temperatures was revealed. This high-throughput method facilitates alloy design as well as provides high-quality data for data mining techniques to accelerate alloy development.