Mechanical properties of Mo5Si3 intermetallics as a function of composition

A solubility range of 2.1 at.% Si at 1600 °C in Mo5Si3 was measured by energy dispersive spectrometry (EDS) in a SEM on samples containing the second phases Mo3Si and MoSi2, respectively. Of the three methods for elemental analysis used in this work, i.e. bulk chemical analysis, EDS, and Rietveld refinement of neutron powder diffraction data, it is concluded that EDS yields an underestimation of Si-content in Mo5Si3 compared to bulk chemical analysis. As a result, the homogeneity range of Mo5Si3 is displaced to lower Si-content compared to the Mo-Si binary phase diagram. Both hardness and toughness of Mo5Si3 displayed their highest values for the composition closest to stoichiometry. The single-phase sample contained Mo vacancies according to Rietveld refinement, which is in good agreement with the results of chemical analysis as these show a slight Mo-deficiency.