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

Abstract

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.