Investigation of reducing agent type on the synthesis behavior and microstructure of Ni-Cr-Mo alloy synthesized by microwave-assisted combustion synthesize

This research investigated the effect of reducing agent type on the synthesis behavior and microstructure of Ni-Cr-Mo alloy, which was synthesized by microwave-assisted self-propagation high-temperature. For this purpose, powder mixtures with the same amount of NiO, MoO3, and Cr2O3 as precursors and different ratios of aluminum to silicon as reductants were prepared. The mixtures were homogenized, compacted to a 20 mm diameter disk, and synthesized by a microwave oven. Results show that although the adiabatic temperature in the silico-thermic sample exceeded the merzhanov criteria, the synthesizing did not occur due to Si high-temperature melting point. The maximum recovery efficiency of Ni and Mo was observed in the Al50 with 92% and 96%, respectively. But, the recovery efficiency of Cr in this sample was 36%, which is very low. Using excess Al in 1.1 and 1.2 times more than the stoichiometric ratio in the Al50ex1.1 and Al50ex1.2 leads to the recovery efficiency of Cr rising 25% and reaching 45%. The presence of residual Si in the produced alloys caused to formation Mo2Ni3Si phase, which is a Mo and Si reach the compound. Microstructural investigation shows residual Si content, and Mo2Ni3Si phase percent were increased by adding excess Al in the initial mixtures. Also, the Mo2Ni3Si proeutectic phase has petaloid morphology. Although the Mo2Ni3Si phase is not formed in the Al100 sample, the severe segregation of Mo led to a continuous network of semi-dual phases in the dendrite boundary.