Structure and mechanical properties of (Mo, Re)Si-2 alloys

Hot hardness tests have been performed on are-melted (Mo, Re)Si-2 alloys at temperatures from ambient to 1300 degrees C. Re is found to be a potent so lution hardening addition to MoSi2 over the entire temperature range, much more than would be expected from their atomic size mismatch or modulus mism atch. In addition ReSi2-x has about twice the hardness of pure MoSi2 at all temperatures. This may be related to the structure of ReSi2-x which nomina lly has the same tetragonal C11(b) structure as MoSi2 but is Si-deficient ( x = 0.25, i.e. the composition is Re4Si7). The Si deficiency is accompanied by some unusual incommensurate periodicities in the structure which themse lves give rise to orthorhombic and monoclinic distortions. The resulting mi crostructure probably explains the high strength of Re4Si7 and the potent h ardening effect of Re in MoSi2 may be due to the accompanying Si vacancies. (C) 1999 Elsevier Science S.A. All rights reserved.