Interfacial microstructure evolution and deformation mechanisms of Ti₃Al vacuum diffusion-bonded joints using a rolled refractory high-entropy alloy interlayer

A rolled refractory high-entropy alloy (HEA) interlayer (Hf₁₅Nb₄₀Ta₂₅Ti₁₅Zr₅) was employed to achieve reliable diffusion bonding of Ti₃Al-based alloys. The effects of bonding temperature on interfacial microstructure evolution and mechanical properties were investigated, and the deformation behavior of the interface was analyzed through in-situ scanning electron microscope-digital image correlation (SEM-DIC) and transmission electron microscopy (TEM) observations. The results reveal that the diffusion reaction layer (DRL) exhibits a continuous B2 solid-solution layer accompanied by nanoscale O-phase precipitation near the Ti₃Al substrate. The joint bonded at 960 °C achieves an optimal tensile strength of 886 MPa and an elongation of 16.6%. Nanoindentation results show smooth hardness and modulus transitions across the interface, confirming the absence of brittle phase. As the overall strain of the sample increases, dislocations accumulate and interact through processes such as intersection and dislocation cell formation, which hinder dislocation slip and thereby strengthen the joint properties. This study provides a feasible design route for diffusion bonding of Ti₃Al-based intermetallics.