Scratch-induced microplasticity and microcracking in zirconium diboride-silicon carbide composite

A ZrB2-5 wt.%SiC composite, consolidated using the plasma pressure compaction technique, was subjected to scratch loads in the range of 50-250 mN using a Berkovich nanoindenter. Microstructural analysis revealed that the scratch grooves consisted of numerous slip bands oriented at random angles to the scratch direction and microcracks oriented perpendicular to the scratch direction. The observed features were rationalized using an elastic stress field due to the combined Boussinesq- and Cerruti-field solutions. The analysis revealed that maximum shear stress occurs ahead of the scratch tool whereas the maximum principal tensile stress occurs in the wake of the scratch tool. Accordingly, it was argued that the slip bands occurred first in the region ahead of the scratch tool due to maximum shear stress while the microcracks developed later due to maximum tensile stress in the wake of the scratch tool. This result was further confirmed by the existence of slip bands ahead of the scratch tip at the exit end of the scratch grooves. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.