Effect of Synthesis Route on Phase Evolution and Microstructural Characteristics of a MoNbSiTiW Refractory High‐Entropy Alloy

Abstract

Silicon‐containing refractory high‐entropy alloys (RHEAs) provide a promising platform for combining a refractory body‐centered cubic (BCC) matrix with thermally stable silicide phases. However, the effects of the processing route on phase evolution and elemental partitioning in Si‐rich RHEAs remain insufficiently understood. An equiatomic MoNbSiTiW alloy was processed by mechanical alloying followed by hot‐press sintering (MA + HPS) and vacuum arc melting (VAM). Both processing routes produced BCC + Nb 5 Si 3 phases but differed significantly in microstructural morphology and elemental distribution. The MA + HPS route resulted in a refined microstructure, with uniformly dispersed Nb‐ and Si‐rich silicide regions within the BCC matrix, whereas VAM produced a coarse dendritic structure with pronounced chemical segregation. These results demonstrate that configurational entropy alone does not suppress silicide formation in the present Si‐rich composition, owing to strong chemical interactions involving Si and refractory elements. Instead, the phase scale and spatial distribution are strongly influenced by solid‐state diffusion and solidification kinetics. Empirical thermodynamic parameters provided qualitative guidance; however, calculation of phase diagrams (CALPHAD) would be required for more rigorous prediction of phase stability and evolution. Overall, the results demonstrate that processing history strongly influences phase architecture and elemental partitioning in Si‐rich MoNbSiTiW RHEAs.