DEFORMATION MECHANISMS IN MOSI2 AT TEMPERATURES ABOVE THE BRITTLE-TO-DUCTILE TRANSITION-TEMPERATURE .1. POLYCRYSTALLINE MOSI2

The deformation mechanisms above the brittle-to-ductile transition tem perature in polycrystalline samples of MoSi2 have been studied. Thus s amples have been deformed at 1200, 1400 and 1600 degrees C respectivel y at a series of strain rates, ranging from 10(-2) to 10(-5) s(-1). Th in foils have been cut from the deformed samples and diffraction contr ast experiments have been performed to determine the identity of the d islocations in the deformed microstructure. Crystallographic analyses have been carried out to determine the line direction of defects, and this information, taken together with a knowledge of the Burgers vecto rs, has been used to assess the degree that slip and climb have occurr ed during deformation. The microstructural evidence is consistent with glide occurring during deformation at 1200 degrees C at all strain ra tes, whereas at 1400 degrees C there appears to be an increasing contr ibution from climb as the strain rate is reduced. At 1600 degrees C, c limb appears to be the dominant deformation mechanism at all strain ra tes. Diffusion data deduced on the basis of the microstructural observ ations are consistent with other estimates of diffusion coefficients d etermined for MoSi2.