Strain inhomogeneities in eutectic composites

Abstract

Transmission and replica electron microscopy have been performed on deformed samples of the as-quenched Ni-W eutectic composite, which deforms extensively by slip in both phases. Two types of strain inhomogeneities were found for samples loaded above the yield point. Longitudinal plastic strain inhomogeneities were a result of the banding of matrix slip. This banding sometimes caused sufficient stress concentrations in the reinforcement phase that it yielded locally at applied stresses well below its macroscopic yield point. Transverse plastic-strain inhomogeneities in the matrix were caused by the preferential yielding of the matrix at or near the reinforcement/matrix interface. The matrix strain gradient caused by this local yielding did not appear to persist for large strains due to the fairly long slip-line length relative to the interfibre spacing. A second mode of transverse strain inhomogeneity was the local yielding of only a fraction of the W fibres intersected by each slip band. Yielding at the reinforcement/matrix interface could be seen to occur at both fibre corners and near ledge-type defects on the flat faces. Because of the severe compatability constraints imposed by the bicrystallike deformation of the composite, secondary slip systems operated locally for plastic strains as low as 0.4%.