Abstract
In order to refine coarse silicide and improve mechanical performance of ternary Nb-20Si-5Mo alloy, ultrasonic vibration treatment for ultra-high temperature melt is successfully applied. The results show that the vibration can improve the fluidity and reduce the shrinkage defects. The hypereutectic microstructure transforms into the fine rod-like eutectic. Due to the solute redistribution in ultrasound field, the Mo-rich layer at Nbss and β-Nb5Si3 phase boundary and the semi-coherent relation can be observed. Mo tends to dissolve in Nbss the matrix phase and inhibit the peritectic reaction. The average size of primary silicide is refined from 49.1 to 2.2 µm with 95.52% refinement efficiency, the compressive strength and fracture toughness of 100 s ultrasonic treated specimen improved 6.84% and 50.75% compared with the as-cast specimen, respectively. The heightened constitutional supercooling and the accelerated nucleation caused by cavitation effect are the main reasons of grain refinement.
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