Shear-Induced Metallization on the (001) and (111) Faces of Diamond during Hardness Tests

For the first time, shear-induced metallization on the (001) face of diamond single crystals of types Ib, IIa and IIb during hardness tests is studied. The tests are performed using the Vickers and Berkovich indenters on diamond single crystals grown by the temperature gradient method. In the Raman spectra of imprints obtained on the (001) face of diamond, intense photoluminescence bands with a complex shape are found, which complicates the identification of the phonon bands of the sp 2 phase of carbon. The sp 2 phase of carbon in the imprints on the (001) face is reliably revealed only for diamonds of type IIb and only in the case of using the Berkovich indenter. It is found that graphitization during hardness tests on the (001) face of diamond of type IIb is much less than on the (111) face. The recorded photoluminescence with a maximum at about 510 nm can be considered as evidence of the formation of the mixed sp 2 / sp 3 phase of amorphous carbon in the imprints on the (001) face of diamond in the initial stages of graphitization.