High-pressure phase transformations occurring in materials are important for a wide range of problems in materials science and engineering. Most of the results in this field have been obtained using high-pressure cells.
In this work, we demonstrate that high-pressure phase transformations also take place during mechanical contact of hard solid materials. These solid-state transformations can be studied by simply combining hardness indentation tests with micro-Raman spectroscopy. In contrast to diamond anvil cell (DAC) experiments, the stress conditions during mechanical contacts are highly non-hydrostatic, i.e. very high shear stresses affect the transformation behavior. Nevertheless, the obtained results can be discussed in the light of the phase transformations as known from DAC experiments. The examples of our research presented here include Si, Ge, SiO2 and ZrO2, and show that phase transformations and amorphization at mechanical contacts are a quite common phenomenon, which has important implications.