Vacuum brazing of medical TA9 alloy to ZrO₂ bioceramics using a biocompatible filler: Interfacial microstructure, mechanical properties and biocompatibility

Based on the principle of developing new biocompatible fillers, the Sn–Zr + AuSn20 filler system was designed. Firstly, the surface of ZrO₂ ceramics was metallized by biocompatible Sn-xZr filler at 900 °C for 20 min. The interfacial microstructure of the Sn–Zr metallization layer/ZrO₂ consisted of β-Sn + Sn₂Zr/m-ZrO₂/t-ZrO₂. Then the pre-metallized ZrO₂ ceramics were brazed to TA9 alloys by AuSn20 metal foil at 550 °C for 30 min. The typical interfacial microstructure of the TA9/ZrO₂ joint is TA9/AuTi₅Sn₃+Sn–Zr/AuSn₄+AuSn₂+Au–Sn–Zr + ZrSn₂/AuSn₄+m-ZrO₂/t-ZrO₂. With the increase of Zr content, the Sn₂Zr phase gradually increases in the metallized layer, the thickness of the AuTi₅Sn₃ layer decreases, the AuSn₄ phase gradually decreases, and the AuSn₂ phase gradually increases in the TA9/ZrO₂ joint. Besides, the optimal shear strength of 46.5 MPa is obtained at 550 °C for 30 min with 6 at.% Zr content. At this point, the joint fractures at the interface of the AuTi₅Sn₃ and AuSn₄ layers, which is a weak area of the joint. Only a little amount of m-ZrO₂ is changed from t-ZrO₂ inside the t-ZrO₂ substrate; the majority of m-ZrO₂ grows directly on the t-ZrO₂ substrate surface. All materials have no cytotoxicity, and even the Sn–Zr metallization layer can promote cell proliferation.