Phase formation during mechanically activated annealing of nanocrystalline Cr-60at.%Al

Evolution of phases during mechanically activated annealing (MA2) of nanocrystalline Cr-Al powder blend with peritectic Cr40Al60 composition was investigated. Significant interdiffusion was observed during MA2 at a low temperature of 400 °C, which led to the formation of various Cr-Al phases viz. tetragonal (I4/mmm) Cr2Al, rhombohedral (R3m) Cr9.5Al16 and the high temperature cubic (I-43m) β-Cr5Al8. Such diffusion-induced phase formation was observed only at a higher temperature of 850 °C in case of a coarse (∼50 μm) grade Cr-60at.%Al precursor. Hexagonal (P63/mmc) Cr2AlC phase was also obtained on annealing of the ball-milled nanocrystalline precursor. The carbide phase formation was attributed to the presence of milling-induced C-contamination (∼2.65-2.80 wt.%) in the ball-milled precursor. The Cr2AlC phase apparently evolved from Cr2Al in the temperature range of 400-850 °C.