Application of diffusion bonding model to superplastic γ -TiAl alloys

Abstract

In the present work, the superplastic characteristics of some γ-TiAl alloys were analysed on the bases of experimental data reported in previous work, and their suitability for diffusion bonding was examined. The constitutive equation ∊ = A DGb/kT (b/d)^p (σ−σ ₀ /G)ⁿ can be used to describe superplasticity in γ-TiAl alloys, and the equation predicts n=2, p=2, and activity energy Q=220 kJ mol⁻¹. It is suggested that the diffusion bonding model for γ-TiAl alloys should be considered two stages, i.e. a plastic deformation stage and a void shrinkage stage including both a diffusion controlled process and a plastic controlled process. Theoretical predictions for obtaining good bonding conditions were in good agreement with experimental results. Using a theoretical bonding model, a prediction map showing the relationship among temperature, applied stress and time for high quality diffusion bonding of superplastic γ-TiAl alloys was obtained.