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 degrees 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) beta-Cr5Al8. Such diffusion-induced phase formation was observed only at a higher temperature of 850 degrees C in case of a coarse (similar to 50 mu m) grade Cr-60at.%Al precursor. Hexagonal (P6(3)/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 (similar to 2.65-2.80 wt.%) in the ball-milled precursor. The Cr2AlC phase apparently evolved from Cr2Al in the temperature range of 400-850 degrees C. (C) 2010 Elsevier B.V. All rights reserved.