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°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 °C for 10min leads to the nanocrystalline phase of TiAl(y), nanocrystalline phases of mainly Ti Al(y) together with Ti3Al(a2) were formed in Cr containing powders. Cr accelerated the production of duplex structure (y+a2) and It seemed that the Cr (Ti, Al) solid solution was dissolved in TiAl(y) and Ti3Al(a2).