Effect of Cr on the evolution of microstructures in as-cast ternary niobium-silicide-based composites

The aim of this report is to present the effect of chromium on the detailed microstructural evolutions in Nb-Si-Cr ternary alloys. The microstructural characteristics of as-cast Nb-Si-Cr ternary alloys with five different compositions have been studied using SEM and XRD. In addition, the lattice parameter and the microhardness of the constituent phases were also estimated. The microstructures of the investigated alloys primarily reveal the presence of three phases: (Nb, Cr, Si)ss, Nb5(Six, Cry)3 and Nb(Crx, Siy)2. The nature, morphology and the amount of the phases, as well as that of the eutectic domains, are found to vary with the composition of the investigated alloys. The lattice parameter of the (Nb, Cr, Si)ss phase decreases, whereas that of the silicide phase first increases and then decreases with increasing concentration of Cr in the investigated alloys. The effect of Cr on the microhardness of (Nb, Cr, Si)ss is more significant compared to that of the adjacent silicide, or the laves phase or that of the eutectic domains.