SYNTHESIS OF NANOSTRUCTURE Ti-45Al-5Cr ALLOY BY MECHANICAL ALLOYING AND STUDY THE EFFECT OF Cr ADDITION ON MICROSTRUCTURE OF TiAl ALLOY

In this work, mechanical alloying was employed to produce Ti-50Al and Ti-45Al-5Cr (at %) alloys. Alloying was performed in a planetary mill and the alloying time varying from 5 to 70 h. Characterization of the powder mixture was performed by X-ray diffraction (XRD) technique, Scanning Electron Microscopy (SEM) and Differential Thermal Analysis (DTA), during mechanical alloying and after annealing treatment at 1100 degree C in vacuum furnace. The results showed; only a complete amorphous phase was detected after 50h of milling of Ti-50Al powder blends but with 5 at % addition of Cr, the Cr (Ti, Al) solid solution phase within the amorphous matrix were formed. While annealing of the mechanically alloyed Ti-50Al powders at 1100 degree C for 10min leads to the nanocrystalline phase of TiAl( gamma ), nanocrystalline phases of mainly Ti Al( gamma ) together with Ti sub(3)Al( alpha sub(2)) were formed in Cr containing powders. Cr accelerated the production of duplex structure ( gamma + alpha sub(2)) and It seemed that the Cr (Ti, Al) solid solution was dissolved in TiAl( gamma ) and Ti sub(3)Al( alpha sub(2)).