Interfacial Microstructure and Mechanical Properties of Titanium/Sapphire Joints Brazed with AuSn20 Filler Metal

In this study, C-plane (0001) sapphire was successfully brazed to titanium using AuSn20 filler metal, following metallization on the surface of the sapphire with Sn-3Ti (wt.%). At 1000 °C, Sn-3Ti had good wettability on the surface of the sapphire, with the lowest equilibrium contact angle of 57°. The reaction phases in the joints were identified, and the typical interfacial microstructure of the brazed joint brazed at 550 °C for 30 min was titanium substrate/Au-Sn-Ti layer/Ti6Sn5 + AuSn2 + AuSn4 + massive Au-Sn-Ti/TiO phase/sapphire. The shear test was utilized to evaluate the bonding strength of the titanium/sapphire joints. The highest shear strength reached 18.7 MPa when brazed at 550 °C for 35 min. The crack was initiated at the sapphire/brazing seam interface and propagated into the Au-Sn-Ti reaction layer.