Measurement of scratch-induced residual stress within SIC grains in ZrB2-SiC composite using micro-Raman spectroscopy

An analytical framework for determination of scratch-induced residual stress within SiC grains of ZrB2-SiC composite is developed. Using a secular equation that relates strain to Raman-peak shift for zinc-blende structures and the concept of sliding blister field model for scratch-induced residual stress, explicit expressions are derived for residual stress calculation in terms of phonon deformation potentials and Raman peak shift. It is determined that, in the as-processed composite, thermal expansion coefficient mismatch between ZrB2 and SiC induces compressive residual stress of 1.731 GPa within the SiC grains and a tensile tangential stress of 1.126 GPa at the ZrB2-SiC interfaces. With increasing scratch loads, the residual stress within the SiC grains becomes tensile and increases in magnitude with scratch load. At a scratch load of 250 mN, the calculated residual stress in SiC was 2.6 GPa. Despite this high value, no fracture was observed in SiC grains, which has been rationalized based on fracture strength calculations from Griffith theory. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved