Plastic deformation of galena (lead sulphide)

Abstract

The stress-strain behaviour and plastic deformation mechanisms of galena crystals in nine orientations and of two types of polycrystalline galena have been studied in compression at room temperature and confining pressures up to 5000 bars. The behaviour of single crystals is strongly orientation dependent but, with the exception of the orientation 〈001〉, depends very little on confining pressure. Also, in the orientation 〈001〉, crystals with large ratios of initial length to cross-section area work harden more rapidly and have greater ultimate strength than crystals with small ratios. Polycrystalline aggregates are generally stronger and more sensitive to confining pressure than single crystals. {001}〈110〉 is the normal slip system in both single crystals and aggregates. However, in the orientation 〈001〉, there is evidence for {110}〈1̄10〉 slip and in special cases, mechanical twinning with composition plane (441) may occur. {110}〈1̄10〉 slip probably also occurs in aggregates. In addition, kinking involving {001}〈110〉 double slip occurs in one single crystal orientation and in aggregates. Deformed single crystals recrystallize when heated for times of 120-4 hr at temperatures of 400–600°C.