Studies of contact damage in polycrystalline zinc sulphide

Deformation processes within the grains and grain-boundary sliding are responsible for the formation of the porous zone and the various crack systems around plastic indentations in chemically vapour deposited (CVD) zinc sulphide. The porous zone is formed by gross grain-boundary displacements in the region directly beneath the indenter and all the cracks emanate from around the porous zone and are contained within an extensive plastic zone. For the particular grain orientation used, the material behaves in an ideal elastic/plastic manner with the development of shear flow lines within the porous zone; the interaction of the flow lines with each other or continued slip along the flow lines lead to preferential void nucleation. The porous zone forms at an average representative strain of about 2.5% and a corresponding pressure of 1.5GPa which is twice the yield stress.