Diffusion-bonding of TiAl

Abstract

Diffusion-bonding of TiAl (48 at.% Al) using both solid-state and transient-liquid-phase (TLP) processes was studied. In solid-state diffusion-bonding, dynamic recrystallization which occurs at the bond-line during bonding is found to have a significant effect on improving bond strength. The use of interlayers in the solid-state process makes it possible to fabricate bonds at a comparatively low bonding temperature and pressure, and to produce bonds having overall properties compatible with the base material after diffusion of interlayers using post-bond heat treatments. In the TLP process, the bonding temperature, which is determined by the melting temperature of the filler alloys, controls diffusion and any interaction between the base material and filler alloy. Ternary inter-metallic phases may form when using low-melting-temperature filler alloys but were not found when using high-melting-temperature filler alloys. The high-melting filler alloys can be used confidently to produce TLP bonds with good mechanical properties. Post-bond heat treatments are found to change microstructural constituent ratios and to affect properties of both the base material and TiAl joints, especially when interlayers or filler alloys are used. The beneficial effect of interlayer or filler alloy elements on bond properties through post-bond heat treatments is remarkable, resulting in the overall properties of bond regions being better than those of the base material.