Abstract
Ni-20wt%Al and Ni-30wt%Al powders were prepared from crystalline powders of Ni and Al by the mechanical alloying for relatively short time (108ks). The X-ray diffraction analysis(XRD) showed any compound in as-milled powders. The reaction in heating of these powders was investigated by the differential thermal analysis and the phase formation in powders was observed by XRD and EPMA.
At temperature below eutectic, because the diffusion of Ni in Al grains was prior to that of Al in Ni, Al-solid solution, Al3Ni and Al3Ni2 were formed in order in Al grains, as the temperature increase. At the eutectic temperature, the formation of eutectic melt triggered to nucleate a large number of AJNi3 in Ni grains, followed by the nucleation of AINi. At temperature above eutectic, the stable phase of alloy gradually grew and became predominant as Al continued to diffuse from Al-rich phase to Ni grains. hi a commercial Ni-20wt%Al powder, the reaction in heating was same as that of mechanically alloyed powder, but only a small amount of Al-rich compounds were formed at a low temperature range.
