China Foundry (Mar 2013)
Microstructure evolution and mechanical properties of homogenizing treated fully lamellar Ti-46Al-0.5W-0.5Si alloy
Abstract
The microstructure of as-cast Ti-46Al-0.5W-0.5Si alloy exhibits significant microinhomogenetity due to the non-equilibrium solidification and low atom diffusion rate. In order to reduce the adverse effect of this microsegregation on plasticity, the microstructure evolution of the Ti-46Al-0.5W-0.5Si alloy homogenized at different temperatures from 1,200 ℃ to 1,320 ℃ was investigated, and the optimized process of homogenizing treatment, i.e., annealing treated at 1,280 ℃ and held for 8 h, was determined. Microstructures of both the as-cast and heat treated alloys were observed by means of optical microscope and scanning electron microscopes. Tensile tests at room temperature were conducted on the homogenizing treated fully lamellar Ti-46Al-0.5W-0.5Si alloy with loading axis parallel to the lamellar interface. Results show that, at higher heat treatment temperatures, the W element diffuses sufficiently, the microstructure tends to be more homogeneous, and the profile of the silicide clusters becomes smooth. Heat treating conducted in the α+γ two phase region can keep the columnar grains and the original lamellar orientation within them. The microstructure of the alloy after heat treated in α+γ two phase region exhibits the coexisting morphology of coarse lamellar and thin lamellar. The homogenization process at 1,280 ℃ for 8 h can significantly reduce the microsegregation, and the elongation at room temperature can increase from 0.48% (as-cast) to 1.34%.
