Rapid solution hardening at elevated temperatures by substitutional Re alloying in MoSi2

The mechanical properties of solidification processed polycrystalline MoSi2 and ternary (Mo, Re)Si2 alloys were evaluated by compression testing at elevated temperatures. Rhenium is found to be a potent solid solution hardening addition to C11b MoSi2 at temperatures up to 1,600 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 had has a Si-deficient stoichiometry of ReSi1.75, the addition of Re to MoSi2 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 MoSi2. Small additions of Re may provide the necessary high temperature strength in MoSi2-based structural intermetallic alloys for very high temperature applications (∼1,200--1,600 C)