Rapid solution hardening at elevated temperatures by substitutional Re alloying in MoSi 2

Abstract

The mechanical properties of solidification processed polycrystalline MoSi 2 and ternary (Mo, Re)Si 2 alloys were evaluated by compression testing at elevated temperatures. Rhenium is found to be a potent solid solution hardening addition to C11 b MoSi 2 at temperatures up to 1600°C (highest temperature used in the study). Dislocation microstructures, characterized by electron microscopy, are consistent with the significant hardening exhibited by Re containing alloys. The high hardening rate cannot be explained by the classical substitutional solid solution hardening theories for metals based on atomic size misfit and elastic moduli mismatch. Since rhenium “disilicide” is semiconducting and has a Si-deficient stoichiometry of ReSi 1.75, the addition of Re to MoSi 2 may lead to the formation of constitutional Si vacancies which may pair with Re substitutionals to form point defect complexes. A model that describes the elliptical strain field (tetragonal distortion) around these point defects is used to interpret the rapid hardening by Re in MoSi 2. Small additions of Re may provide the necessary high temperature strength in MoSi 2-based structural intermetallic alloys for very high temperature applications (∼1200–1600°C).