Raman microspectroscopy of nanocrystalline and amorphous phases in hardness indentations

During hardness indentation, materials are subjected to highly localized st resses. These stresses not only cause crack formation and plastic deformati on by dislocation gliding, but a complete change of the crystal structure a nd formation of amorphous phases or high-pressure polymorphs can occur in t he zone of maximum contact stresses. Such contact-induced phase transformat ions were observed in hard and brittle materials including semiconductors ( Si, Ge, GaAs and InSb) and common ceramic materials such as SiC and SiO2 (a lpha-quartz and silica glass). A prime tool for their investigation is the Raman microspectroscopy of hardness indentations. In Si and Ge, there is an initial transformation to metallic high-pressure phases upon hardness indentation and a subsequent formation of crystalline, nanocrystalline, or amorphous phases depending on the conditions of the ha rdness test, in particular the unloading rate. A phase transformation occur s also in InSb, whereas the results for GaAs do not give sufficient evidenc e for phase transformations. Indentation-induced amorphization has been obs erved in SiC and quartz, Even diamond has been shown to undergo amorphizati on and phase transformation under nonhydrostatic stress conditions imposed by indentation tests. Copyright (C) 1999 John Wiley & Sons, Ltd.