A Comparison between the Effect of Cr and W Addition on Formation Kinetic of Nanostructure TiAl(γ) Alloy by Mechanical Alloying Route

In this research, mechanical alloying was used to produce Ti-50Al, Ti-45Al-5Cr and Ti-45Al-5W (at%) alloys. The effect of ternary addition (Cr and W) on microstructure and production efficiency of TiAl alloy were investigated. Alloying was performed in a planetary mill and the milling time varying from 5 to 70h. The structural evaluation in these powders was done by X-ray diffraction (XRD) technique and Scanning Electron Microscopy (SEM) during mechanical alloying and after annealing at 1100°C in vacuum oven. The results showed only a complete amorphous phase after 50h of milling of Ti-50Al powder mixture, but with 5at% addition of Cr, the Cr (Ti, Al) solid solution within the amorphous matrix were identified after 70h milling and with 5at% addition of W, the W lattice was remained with amorphous phase. The time required for solid solution or amorphous phase formation was longer in Cr and W containing powders. After annealing of mechanically alloyed Ti-50Al, the γ-phase with high purity and nanostructured size was produced and for sample with Cr addition, the TiAl(γ) with amount of Ti3Al(a2) were formed and for sample with W addition, the duplex phase (γ+a2) with a minor amount of W, were formed.