Insight into the strengthening effect of Nb foil on Al₂O₃/TNZ joints brazed by TiNiNb filler: Interface reinforcement and stress relief

Reliable joining of Al₂O₃ ceramic to Ti-13Nb-13Zr (TNZ) alloy for implantable medical device seals was achieved using a biocompatible Ti₄₀Ni₄₀Nb₂₀/Nb foil composite filler. The effects of brazing temperature and holding time on the interfacial microstructure and mechanical properties of the Al₂O₃/TNZ joint were systematically investigated. The typical interfacial microstructure of the joint consists of Al₂O₃/Al(Nb,Ti)Ni + Ni₂Ti₄O + m-ZrO₂/Ti₂Ni + (Nb,Zr,Ti)ss/(Nb,Ti)ss/(Ti,Nb)ss/ Nbss/Ti₂Ni + (Ti,Nb,Zr)₃Ni + Tiss/TNZ. The introduction of the Nb foil promotes the formation of the Al(Nb,Ti)Ni phase, improving the brazing seam/ Al₂O₃ ceramic interface bonding. Meanwhile, it effectively relieves residual thermal stress in the Al₂O₃/TNZ joint by forming a gradient elastic modulus layer and acting as a ductile interlayer. Under the condition of 1160 °C for 10 min, the shear strength of the joint reaches 52.2 MPa. This study provides a new low-cost and high-strength solution for the sealing of biomedical implantable devices.