DIFFUSION-BONDING OF TIAL

Diffusion-bonding of TiAl (48 at.% Al) using both solid-state and tran sient-liquid=phase (TLP) processes was studied. In solid-state diffusi on-bonding, dynamic recrystallization which occurs at the bond-line du ring bonding is found to have a significant effect on improving bond s trength. The use of interlayers in the solid-state process makes it po ssible to fabricate bonds at a comparatively low bonding temperature a nd 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 i s determined by the melting temperature of the filler alloys, controls diffusion and any interaction between the base material and filler al loy. Ternary intermetallic phases may form when using low-melting-temp erature filler alloys but were not found when using high-melting-tempe rature filler alloys. The high-melting filler alloys can be used confi dently to produce TLP bonds with good mechanical properties. Post-bond heat treatments are found to change microstructural constituent ratio s 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 throu gh post-bond heat treatments is remarkable, resulting in the overall p roperties of bond regions being better than those of the base material .