Study on microwave synthesis and characterisation of bulk nickel aluminides

Abstract

Combustion synthesis of Ni–Al intermetallic compounds from 1∶1 molar mixtures of aluminium and nickel powders subjected to microwave (MV) heating has been investigated. Preliminary experiments confirmed that the usage of silicon carbide susceptor could successfully result in the preparation of bulk products in a fast and reproducible manner. The effect of the degree of compaction of the powder mixture and applied MV power on the ignition time, as well as the composition, microstructure and microhardness of the final products, was examined. Decreasing the compact porosity made the grain size of intermetallic products decrease and the microhardness increase. Variation of MV power at a constant degree of compaction did not affect the product grain size and microhardness. However, it had a distinct influence on the product composition; applying MV power of 1100 W on samples with moderate compactness resulted in NiAl, whereas that of 440 W produced Al₃Ni₂. Ni₃Al precipitates were also identified when both the compaction pressure and the MV power were high. Moreover, a negative linear relationship was found between ignition time and MV power.