Interfacial Microstructure of Silicon Carbide and Titanium Aluminide Joints Produced by Solid-State Diffusion Bonding

Abstract

This paper describes the microstructure and the formation mechanism of solid-state diffusion bonded interfaces of silicon carbide (SiC) and titanium aluminide (TiAl). Two SiC specimens were diffusion bonded using a Ti-48 at%Al foil in vacuum. The interfacial microstructure has been investigated by means of scanning electron microscopy, electron probe microanalysis and X-ray diffraction. Four layers of reaction products are formed at the interface by diffusion bonding: a layer of TiC adjacent to SiC followed by a diphase layer of TiC+Ti₂AlC, a layer of Ti₅Si₃C_X containing Ti₂AlC particles and a layer of TiAl₂. However, the TiAl₂ layer is formed during cooling. The actual phase sequence at the bonding temperatures of 1573 K and 1673 K are SiC/TiC/(TiC+Ti₂AlC)/(Ti₅Si₃C_X+Ti₂AlC)/Ti_1−XAl_1+X/TiAl and SiC/TiC/(TiC+Ti₂AlC)/(Ti₅Si₃C_X+Ti₂AlC)/Ti₅Al₁₁/Ti_1−XAl_1+X/TiAl, respectively. Ti₅Al₁₁ and Ti_1−XAl_1+X rapidly transform to TiAl₂ during cooling. The layers grow obeying the parabolic law. The growth rate of the reaction layers change sensitively depending on the bonding temperature.