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

The mechanical properties of solidification processed polycrystalline MoSi2 and ternary (Mo, Re)Si-2 alloys were evaluated by compression testing at e levated temperatures. Rhenium is found to be a potent solid solution harden ing addition to C11(b) MoSi2 at temperatures up to 1600 degrees C (highest temperature used in the study). Dislocation microstructures, characterized by electron microscopy, are consistent with the significant hardening exhib ited by Re containing alloys. The high hardening rate cannot be explained b y the classical substitutional solid solution hardening theories for metals based on atomic size misfit and elastic moduli mismatch. Since rhenium "di silicide" is semiconducting and has a Si-deficient stoichiometry of ReSi1.7 5, 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 co mplexes. A model that describes the elliptical strain field (tetragonal dis tortion) around these point defects is used to interpret the rapid hardenin g by Re in MoSi2. Small additions of Re may provide the necessary high temp erature strength in MoSi2-based structural intermetallic alloys for very hi gh temperature applications (similar to 1200-1600 degrees C). (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.