An analysis of the microstructures developed in experimentally deformed polycrystalline pyrite and minor sulphide phases using electron backscatter diffraction

Abstract

Samples of polycrystalline pyrite previously deformed in tri-axial compression tests at a confining pressure of 300 MPa and a strain rate of 2 × 10 −4 s −1 but varying temperature were analysed in this study. Five samples including the original starting material have undergone analysis using forescatter orientation contrast (OC) imaging coupled with electron back scatter diffraction (EBSD) to determine how the micro-structures in pyrite and to an extent the surrounding minor phases have changed with increasing temperature. Between 550 °C and 650 °C the dominant deformation mechanism in pyrite is that of dislocation creep. Above 650 °C this mechanism becomes less apparent and few if any dislocation walls are present within pyrite grains by 700 °C. This is a result of either increased dynamic recrystallisation with temperature or a change in the dominant deformation mechanism. Dislocation creep occurs via lattice rotation, principally about a single 〈100〉 axis, but also about two separate 〈100〉 axes and more rarely about a single 〈110〉 axis. Deformation has not resulted in a crystallographic preferred orientation (CPO) within any of the samples. Shape change of pyrite grains has occurred and this can account for most if not all of the shortening applied, but dynamic recrystallisation of pyrite and grain boundary sliding accommodated along the minor phases are also likely to be important mechanisms in all of the samples.