Synthesis and properties of MO5Si3 single crystals

The ultra-high temperature structural intermetallic Mo5Si3 has been studied for alloy processing, physical properties, and mechanical behavior. High p urity single crystals of Mo5Si3 have been synthesized by both optical float ing zone and Czochralski methods. Structural, thermal, and elastic properti es of Mo5Si3 single crystals were measured by X-ray powder diffraction, the rmal mechanical analysis, and resonant ultrasound spectroscopy, respectivel y. Results show that the thermal expansion of MO5Si3, a tetragonal structur e with I4/mcm symmetry, is strongly anisotropic along the a and c direction s with alpha(c)/alpha(a) = 2.2. Single crystal elastic moduli of Mo5Si3 ind icate that it has less elastic anisotropy and lower shear modulus than most transition metal disilicides. The impacts of these physical properties on alloy processing and mechanical behavior are discussed. Room temperature Vi ckers indentation tests on the (100) and (001) planes have been performed f or different orientations of the indenter diagonal and the corresponding ha rdness, fracture toughness, and deformation behavior have been obtained as a function of the crystallography. Finally, the physical properties and mec hanical behavior of Mo5Si3 are compared with those of other high temperatur e structural silicides, e.g. MoSi2. (C) 1999 Elsevier Science Ltd. All righ ts reserved.