Structural damage in boron carbide under contact loading

A systematic study of mechanical deformation of boron carbide under contact loading is conducted using scratching and depth-sensing indentation (nanoindentation). Both single crystal and polycrystalline materials are investigated by means of Raman microspectroscopy and transmission electron microscopy (TEM). High resolution TEM images of scratch debris reveal various microstructural changes including formation of nanocrystals, as well as lattice shearing and distortion on nanoscale. Deformation bands and microcracks oriented along the (1 1 3) planes are visible in cross-sectional TEM micrographs of indentations. Narrow amorphous bands and local disordered areas are observed in plan-view TEM images. Evidence for a high-pressure amorphous phase is also presented. It is concluded that scratching and nanoindentation change the microstructure of boron carbide in a similar manner. In addition, the evidence for formation of sp(2) hybridized carbon as a result of structural changes induced by contact loading is found by electron energy loss spectroscopy (EELS). (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.