Microstructure evolution of WMoNbTiCrAlx (x = 0, 0.25, 0.5, 0.75, 1) multi-principal element alloys

Abstract

Multi-principal element alloys (MPEAs) based on refractory metals have been studied as potential candidates to replace Ni-based superalloys due to their superior melting temperatures and the promising initial high-temperature properties demonstrated by certain compositions. However, a significant drawback of these refractory metal-based alloys is their high density and low ductility at room temperature. It is known that the addition of Al in MPEAs contributes to reducing density, increasing hardness, and stabilizing the BCC phase. In this study, the influence of Al on the microstructure of five new multi-principal element refractory alloys produced by arc melting, using high-purity raw elements, WMoNbTiCrAlₓ (x = 0, 0.25, 0.5, 0.75, and 1), was analyzed. ThermoCalc software was utilized to support the interpretation of the experimental results. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed on all alloys in both as-cast and heat-treated (1200 °C/24 h) conditions. Additionally, electron backscatter diffraction (EBSD) analyses were performed on the heat-treated alloys. The as-cast alloys exhibited a highly segregated BCC phase with a dendritic structure. After heat treatment, the alloys predominantly presented a BCC phase, with a small volume fraction of the Laves phase being observed. Nanoindentation tests indicated that the addition of Al increases hardness, from 10.5 to 12.2 GPa. Regarding density, there was a decrease with increasing Al content, from 9.7982 to 8.7745 g/cm³.