Interfacial reactions and microstructural instability mechanisms in TLP bonding of AISI 316 L/WC–10Co using a Ni–Co–Fe–Cr–B–Si multi-principal-element interlayer

To address complex interfacial reactions and microstructural instability during transient liquid phase (TLP) bonding of AISI 316 L/WC–10Co, a Ni–Co–Fe–Cr–B–Si multi-principal-element interlayer was designed. CALPHAD calculations, DSC, interrupted bonding experiments, and multiscale characterization were used to investigate melting, isothermal solidification, interfacial reactions, and elemental redistribution. At 1060 °C, an appropriate amount of transient liquid formed, while continuous diffusion of B and Si into both base materials drove bidirectional isothermal solidification. The residual liquid at the joint center progressively fragmented, and the solidification fronts essentially converged after ~180 min, forming a continuous FCC-solid-solution-dominated bonding zone. On the WC–10Co side, Co binder restructuring and limited WC dissolution produced an η-like reaction zone. With increasing holding time, B and Si segregation at the joint center progressively decreased owing to their outward diffusion into both base materials and the resulting isothermal solidification, whereas localized W and Cr enrichment on the WC–10Co side intensified. Prolonged holding promoted brittle-phase connectivity, pore agglomeration, and microcracking, causing the joint properties to first increase and then decrease. The joint stability is therefore governed by competition between central-region homogenization and localized reactions on the WC–10Co side.