Tensile behavior and failure mechanism of Inconel 617 superalloy diffusion-bonded joints with Ni insert layer

To address the strength-ductility trade-off in diffusion-bonded joints of Inconel 617 superalloys, this paper proposes an interface optimization strategy based on insert layer thickness regulation. Using Inconel 617 alloy as the base material, diffusion bonding was performed with pure Ni foils of varying thicknesses (3-100 μm) as insert layer. The effects of insert layer thickness on the mechanical response and microstructural evolution of the joints were systematically investigated. Results show that joint properties do not evolve linearly with thickness. In-situ tensile electron backscatter diffraction (EBSD) characterization revealed that the 30 μm joint exhibits a dispersed network-like distribution of geometrically necessary dislocation (GND) density, effectively alleviating stress gradients at the interface. In contrast, the 100 μm joint undergoes severe strain localization, with GND density one order of magnitude higher than that of 30 μm insert layer joints, leading to early plastic instability. This study confirms that precisely controlling insert layer thickness to optimize geometric constraint effects and strain distribution patterns is key to achieving high-strength and high-toughness connections in dissimilar metals.