Influence of Rare Earth Elements on the Structural-Phase State of Mo–Si–X (X = Sc, Y, Nd) in situ Composites

Abstract

The microstructure and phase composition of the Mo-Si alloy doped with Sc, Y or Nd were investigated. The methods of X-ray diffraction analysis (XRD), electron microscopy, and electron probe microanalysis (EPMA) were used to determine the main phase components and their volume fractions as well as to assess the speciation and interphase distributions of doping rare earth elements (REE). It was shown that, when introducing up to 3.0 at % Si, Y, or Nd into the Mo–15.3 at % Si hypoeutectic alloy, the structure intrinsic to naturally occurring (in situ) composites was formed. This structure was composed of an α-Mo based solid solution and a strengthening silicide phase including Mo3Si and the particles of complex composition enriched in REE. Doping additives contributed significantly to the microstructure dispersity and modified the morphology of particles of both the metallic and silicide phases, and increased the Mo_ss/Mo₃Si volume ratio. The microhardness of structural components was determined and the parameters of lattice elementary cells of the main phases were evaluated for the REE-doped alloys under study. The observed regularities of their variations generally conformed to the conclusions about the influence of REE on the structural-phase state of the Mo-Si hypoeutectic composites.