Phase transformations during indentation

When applied to the study of phase transformations during indentation, Raman spectroscopy drastically extends the electron microscopy results. Raman spectra indeed reveal amorphous silicon within the indentation area [64, 116] however, they also indicate that the formation of a-Si strongly depends on the experimental conditions [64]. Figure 17 shows the Raman spectra obtained from various points around Rockwell indentations in silicon. The original Si-I phase is observed outside the contact area, which is confirmed by a single Raman line at 520 cm (Fig. 17a). In contrast, the Raman spectra taken from the indentation area look... 

It can be easily shown that compressive uniaxial or biaxial stress results in the upshift of the Raman band to higher wavenumbers, whereas tensile stress decreases the Raman frequency in these cases [47]. However, in the complex stress field under the indenter, further complicated by the volumetric changes during possible phase transformations and the breakdown of constitutive equations due to macro- and microcracking, determination of the strain tensor components becomes a challenging task and the simplifying analytical models already discussed here need to be used. 

Although the values of metallization pressures in InSb are fairly low, there is no evidence of pressure-induced transformations to metallic phases during indentation. The hardness vs temperature dependence in InSb [5, 169] is similar to that... 

Nanoindentation is a powerful technique because the shape of the load-displacement curve can be used to identify effects such as phase transformations, cracking, and film delamination during indentation. It is also important in studying the mechanical properties of nanomaterials, such as carbon nanotubes. There is reference now to a picoindenter, which is a combination of a nanoindenter and an atomic force microscope (AFM). 

Fig. 10. Resistance of silicon during slow indentation in the [100] direction (a) experimental setup and (b) resistance vs pressure curve. The initial large change in resistance is due to the gradual change in contact area. Abrupt drop in resistance at 12 GPa is an indication of the transformation of silicon under loading into a metallic phase. After Reference [86].

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