Microstructure and formation mechanism of Ni-Al intermetallic compounds fabricated by reaction synthesis

Ni-Al intermetallic compounds from Ni and Al powder were obtained by thermal explosion. Effects of molar ratio of Ni to Al in raw materials on the phases, microstructures and microhardness of the final products were studied. The results show that a single phase of NiAl is obtained with the composition corresponding to n(Ni):n(Al)=1:1. However, when the molar ratio of Ni to Al increases to 2:1, the product is composed of Ni3Al and NiAl, in which NiAl phase is in the majority with an irregular morphology and Ni3Al is in the minority mainly along the grain boundary of the NiAl. As the molar ratio of Ni to Al continues to increase to 3:1, the microstructures of the product are diversified. Lots of M-NiAl with needle-like or long lathing shape and many γ′-Ni3Al with irregular and pointed strip-like morphology even appear besides β-NiAl with dendritic structure, γ-Ni3Al with irregular or net-like morphology because of the non-equilibrium cooling and large difference in composition of β-NiAl.