Grain refinement of combustion-synthesized NiAl by addition of ceramic particles

A bulk material of NiAl has been combustion-synthesized from the mixture of nickel and aluminum powders by using a pseudo-hot-isostatic-pressing (PHIP) method, and the effects of the addition of Al2O3, SiC or NiAl particles on the microstructure, mechanical properties at roon temperature and oxidation resistance at a temperature of 1500 K have been investigated. The maximum volume fraction of the added particles is 10%, and the particle size is varied from 0.5 to 130 μm. The density and hardness of the combustion-synthesized NiAl significantly increase witl the PHIP pressure. The addition of each type of particles significantly reduces the grain size of the synthesized NiAl. The added Al2O3 particles segregate at the grain boundary of the synthesized NiAl, while the added SiC particles decompose into silicon and carbon during the synthesis, and only silicon segregates at the grain boundary of the NiAl. The density of the synthesized NiAl slightly decreases with increasing volume fraction of the added particles, while the relative density remains more than 95%. The addition of the particles has no effect on the hardness of the NiAl. The increase in the volume fraction of the added Al2O3 particles significantly degrades the oxidation resistance of the synthesized NiAl, while very little effect is brought about by the addition of SiC particles and no effect by the addition of NiAl particles.