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).
Highlights
High-entropy alloys (HEAs), consisting of four or more elements with each concentration between 5 and 35 at.%, exhibit various composition designs, interesting phase transformations, and noble properties
The diffusion bonding of CoCrNi-based medium-entropy alloy to DD5 single-crystal superalloy was performed in a vacuum
The following conclusions can be drawn: (1) The typical diffusion zone with a width of 6.9 μm was formed by diffusion bonding at 1110 ◦C for 1 h, achieving the reliable joining of medium-entropy alloy (MEA) and DD5 substrates
Summary
High-entropy alloys (HEAs), consisting of four or more elements with each concentration between 5 and 35 at.%, exhibit various composition designs, interesting phase transformations, and noble properties. CoCrNi-based MEAs containing coherent nanoscale γ phase with an L12 superlattice structure, namely ordered FCC structure, are potentially advantageous materials to compete with commercial superalloys [9,10]. The reliable joining of MEAs/single-crystal superalloys can achieve complementary superiorities of both materials, significantly extending the potential applications in areas such as the aviation industry, aerospace engineering, and nuclear energy engineering [14,15]. Diffusion bonding of HEAs (or MEAs) to Ni-based single-crystal superalloys has not yet been reported. Detailed investigation on diffusion bonding of HEAs (or MEAs) to Ni-based single-crystal superalloys is of significant importance for accelerating the realization of engineering applications. The diffusion bonding of CoCrNi-based medium-entropy alloy to DD5 single-crystal superalloy was performed under vacuum. The mechanical properties and crack propagation behavior of the joint under tensile test were elucidated
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