OPTICAL AND MECHANICAL-PROPERTIES OF ZINC-SULFIDE DIAMOND COMPOSITES

Pure ZnS, an infrared transparent but mechanically weak material, was toughened with diamond particles. The optical properties of the pure material were preserved in the composite when the diamond particles were uniformly dispersed. Careful control of the hot pressing parameters was required in order to: (a) limit the phase transformation to a non-cubic phase of ZnS at high temperatures, and (b) maintain a small grain size. Measurement of the reflectivity of this composite in the region of the lattice vibration spectrum was used to compare the measured electrodynamic properties with those predicted by two differential theoretical models that assume different microstructural morphology. Good agreement was found with the Bruggemann model that assumes both components in the composite have the same type of interconnectedness. The mechanical properties of the 10% diamond composite showed a two fold increase in toughness without a change in the hardness with respect to pure ZnS. The bulk modulus and the shear modulus of the composite were measured and were found in agreement with a composite sphere model that assumes a good interfacial bonding between ZnS and diamond. The increase in toughness was explained in terms of the lowering of the local stress intensity factor (relative to the applied value) in the presence of diamond particles. © 1990.