SYNTHESIS OF NANOSTRUCTURED GAMMA-TiAl BASED POWDERS AND BULK ALLOYS USING HIGH ENERGY MECHANICAL MILLING AND HIP

Abstract

The microstructural evolution and powder particle morphology change in the process used to synthesize bulk nanostructured γ- TiAl intermetallic based binary Ti -47 Al (in at%) alloy (TA-1) and complex Ti -45 Al -2 Cr -2 Nb -1 B -0.5 Ta (in at%) alloy (TA-2) have been studied. This process combines high energy mechanical milling of elemental powder mixtures, thermal treatment and HIP. The bulk alloys consist of predominantly TiAl phase and a small fraction of Ti 3 Al phase, with the average grain sizes of the TiAl and Ti 3 Al phases being approximately 45nm and 40nm respectively in the bulk TA-1 alloy and being 37nm and 35nm respectively in the bulk TA-2 alloy. The study also shows that addition of a small fraction of hard powder particles such as Nb , Cr , B and Ta powder particles to the starting powder mixture has a significant effect in maintaining a small average particle size during high energy mechanical milling without using PCA and thus significantly enhances the mechanical alloying effect of the milling process.