Abstract:TiAl intermetallics was diffusion bonded to steel 40Cr in vacuum furnace. The results show that at the TiAl-40Cr interface the mixture reaction layer of Ti₃Al+FeAl+FeAl₂ is formed close to the TiAl base, TiC layer is formed in the middle and obvious decarbonized layer is formed closest to the steel 40Cr side. The whole reaction process can be divided into three stages. In the first stage, TiC layer is formed at the interface TiAl/40Cr, as well, decarbonized layer occurs on the steel 40Cr side. In the second stage, TiAl, FeAl₂ and FeAl are formed adjacent to TiAl, in the mean, the continuous diffusion of Al atoms from TiAl to 40Cr gives rise to the formation of Ti₃Al. In the last stage, the thickness of each reaction layer increases with bonding time according to a parabolic law. The growth energy Q and the growth velocity K₀ of reaction layer Ti₃Al+FeAl+FeAl₂+TiC in the diffusion-bonded joints of the TiAl base alloy to steel 40Cr are 203.017kJ/mol and 6.074mm²/s, respectively, and the growth formula (thickness of reaction layer) is y²=6.074×10^-6exp(-203017.48/RT)t. By virtue of this formula, the growth of reaction layer Ti₃Al+FeAl+FeAl₂+TiC can be presetted and controlled.

Key words:   TiAl intermetallics; interface microstructure; formation mechanism; growth energy; growth velocity