Microstructures and Properties of Refractory Niobium-Silicide-Based Composites

Abstract

The microstructures, mechanical properties and oxidation resistance of the refractory Nb-silicide-based composites have been investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), compression tests and high-temperature oxidation experiments. The results showed that 1773K/100h heat-treatment was an optimum processing for acquiring equilibrium Nb solid solution and silicides microstructure. In the binary Nb-Si system, the microstructure consisted of continuous Nb5Si3 equilibrium matrix and dispersed Nb particles, while in the the Nb-Ti-Cr-Al-Si-(Hf) multicomponent system, there are two typical microstructures, i.e., a two-phase structure of β (Nb solid solution)+D81 Nb5Si3-type silicide in the alloys with the Si+Al content (15at.% and 6at.%, respectively), and a three-phase structure of β+D81 Nb5Si3-type + D88 Ti5Si3-type silicides in the alloys with lower Si+Al content (10at.% and 8at.%, respectively). The results of compression tests showed that all alloys display high strength at both room and high temperatures, only a slight decrease in compression properties occured for Nb-Ti-Cr-Al-Si alloys, comparing to the binary Nb-Si in-situ composites. This type of alloys possesses good high temperature strengths up to at least 1473K. The results of high-temperature oxidation experiments showed that the oxidation rates of the alloys with Ti, Cr, Al and Hf addition were at least one order of magnitude lower than those of the Nb-Si binary alloys.