Local dislocation creep accommodation of a zirconium diboride silicon carbide composite

A grain boundary sliding creep mechanism, accommodated by mantle dislocation activities, is shown to allow for large strain (epsilon > 0.08) during the creep of a ZrB2-20% SiC composite at 1800 degrees C. We characterized the local grain deformation behavior using high-resolution electron backscatter diffraction microscopy and an indentation deformation mapping technique. Deformation gradients near grain boundaries (mantle) produced geometrically necessary dislocation (GND) densities of 1 x 10(11)-1 x 10(12) cm(-2), about two orders of magnitude above that of the grain interiors (core). A deviation from single-crystal grain core deformation defines the mantle where excess GNDs accommodate the grain deformation gradient. Evidence supporting grain boundary sliding as the primary contribution to the creep strain appears in our earlier publication, but we show here the role of dislocations in the deformation of the grain mantle as the rate-controlling accommodation step. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.