Microstructure and Mechanical Properties of Diffusion-Bonded CoCrNi-Based Medium-Entropy Alloy to DD5 Single-Crystal Superalloy Joint

Abstract

This study focuses on the diffusion bonding of a CoCrNi-based medium-entropy alloy (MEA) to a DD5 single-crystal superalloy. The microstructure and mechanical properties of the joint diffusion-bonded at variable bonding temperatures were investigated. The formation of diffusion zone, mainly composed of the Ni3(Al, Ti)-type γ′ precipitates and Ni-rich MEA matrix, effectively guaranteed the reliable joining of MEA and DD5 substrates. As the bonding temperature increased, so did the width of the diffusion zone, and the interfacial microvoids significantly closed, representing the enhancement of interface bonding. Both tensile strength and elongation of the joint diffusion-bonded at 1110 °C were superior to those of the joints diffusion-bonded at low temperatures (1020, 1050, and 1080 °C), and the maximum tensile strength and elongation of 1045 MPa and 22.7% were obtained. However, elevated temperature produced an adverse effect that appeared as grain coarsening of the MEA substrate. The ductile fracture of the joint occurred in the MEA substrate (1110 °C), whereas the tensile strength was lower than that of the MEA before diffusion bonding (approximately 1.3 GPa).

Evaluation of nano mechanical properties and corrosion behavior of diffusion welded CoCrNi medium-entropy alloy (MEA) and SUS 304 stainless steel joints

“…Du et al (2021) successfully performed diffusion bonding on FGH 98 (Ni-based superalloy) and CoCrNi MEA by utilizing Ni interlayer and achieved maximum shear strength of 592 MPa at 1150 °C (Du et al, 2021). Diffusion bonding on CoCrNi MEA and DD5 (Single crystal Ni-based superalloy) was also executed by Li et al (2021b) The joint received maximum tensile strength (i.e. 1045 MPa) and ductility (22.7%) at high bonding temperature (1110 °C).…”