The effect of aluminum substitution on the mechanically induced self-sustaining reaction of molybdenum-silicon powders

Abstract

The effect of Al concentration on the ignition of mechanically-induced self-sustaining reaction (MSR) in Mo + (2 − x)Si + 2xAl powder mixtures has been investigated. When MoSi2 is prepared by SHS method, Al addition results in the formation of Si-Al eutectic and consequently lowers the ignition temperature. In the case of MSR, replacing brittle Si with ductile Al also affects the activation process. The ignition of MSR was investigated as a function of the Al content in a SPEX 8000 Mixer Mill. The ignition time decreased by 30% between x = 0 and 0.08. At the same time, the grain size increased by about 50% according to XRD linewidth measurements. Comparison of SEM images suggests that Al substitution promotes the formation of agglomerates and lamellar structures, although the differences between the binary Mo-Si and Alcontaining samples are very small. Al substitution encourages the formation of hexagonal Mo(SiAl)2 over the tetragonal form of MoSi2. It also promotes more complete conversion during MSR.