Grain rotation and translation contribute substantially to creep of a zirconium diboride silicon carbide composite

Abstract

Electron back scatter diffraction (EBSD) techniques as well as a novel microstructure mapping technique for the direct measurement of local grain-to-grain movements, provided the tools necessary for the assessment of creep deformation mechanisms of a ZrB2–20% SiC composite. Flexure creep behavior determined here draws upon our previous research conducted at 1800°C and 16 through 97MPa for the same composite and within the context of existing creep theory.We found ZrB2 grain deformation scaled with the macroscopic creep strains. To this end, our novel indentation mapping method clearly defined the local ZrB2 grain boundary sliding event, with deformation components of 80% grain translations and rotations, with the remainder attributed to cavitation and other deformations. EBSD kernel average misorientation methods indicated dislocation flow as the local deformation mechanism confined within the ZrB2 near-grain boundary zones, serving solely to accommodate the grain rotation and translation events. Based upon this, we propose a modified grain boundary sliding model accounting for near-grain boundary deformation by dislocation glide and climb, operating in sequence with cavitation.Texture analysis from acquired EBSD pole figures confirmed minimal contribution from SiC grain deformation to the tensile bending component, in contrast with a more significant contribution along the compression zone. We find evidence of <5% and <20% SiC grain deformation, contributing to the macroscopic creep strain, for tension and compression bending fibers, respectively. Cavitation accounts for no more than 5% of the macroscopic creep strain, agreeing with our previous estimates and the balance attributed to ZrB2 grain boundary sliding.