Microstructural characteristics and mechanical response of transient liquid-phase diffusion bonding AlCoCrFeNi_2.1 high entropy alloy utilizing BNi-5 interlayer

This study focuses on the microstructural characteristics and mechanical response of the transient liquid phase (TLP) diffusion-bonded joints of AlCoCrFeNi_2.1 high entropy alloy. Bonging parameters were chosen and optimized for the AlCoCrFeNi_2.1 alloy and the TLP joining mechanism. The relatively complete isothermal solidification zone (ISZ) ensured a reliable connection of the base metal. As the bonding temperature increased from 1060 °C to 1160 °C, the athermal solidification zone (ASZ) disappeared. The homogenization degree of elements in the ISZ continuously increased, the matrix γ phase became fully ordered, and the B2 phase was precipitated, achieving high entropy state in the ISZ of the joint. Additionally, semi-coherent relationships of [0, 1, 1] L1₂, [0, 1, 1] B2 and (1, 1̅,1) L1₂, (2̅, 3, 1̅) B2 were detected between the B2 precipitate phase and the L1₂ matrix. The phase distribution in the ISZ significantly influenced the mechanical properties of the joint. The complete ordering of the matrix phase at 1160 °C eliminated deformation incoordination between the ISZ and the diffusion-affected zone (DAZ). The B2 phase transitioned from precipitating at the grain boundary at lower temperatures to precipitating uniformly in the ISZ, eliminating the weakening effect of the grain boundary and resulting in tensile strength and elongation comparable to the base material. The fracture morphology indicated a mixed fracture mode.