| Description |
Granular diamond composites are particulate reinforced composites, where the particulate phase is a grade of high-hardness polycrystalline diamond, embedded in a tougher, hard-material matrix. Granular diamond composites are hierarchically-structured materials. In addition to the macrostructure and microstructure, granular diamond composites have a mesostructure that encompasses the morphology of the matrix and granules and is characterized by parameters such as component volume fraction, granular sphericity, and matrix uniformity. The mesostructure is functionally designed to improve the performance of the composite in petroleum well-drilling applications by increasing the fracture resistance while maintaining the wear resistance. The impact of the mesostructure on the flexural strength, wear resistance, impact resistance, and in-field performance was measured. Physical testing showed that volume fraction of the tougher, matrix phase can be increased significantly before the wear resistance of the composite decreases appreciably. But the testing also showed that the method developed to produce the composites resulted in component materials with inferior properties. The flexural strength of a polycrystalline-diamond/tungsten-carbide material system was explored using several modeling techniques, including analytic, two-dimensional numeric, and three-dimensional numeric models. Residual stresses, arising from the change in conditions after the material is formed in a high-temperature, high-pressure sintering process, have a significant impact on the calculated strength of the composite. Dilatational residual stresses have never been treated in a rigorous manner in the literature and are often neglected completely. In this study, the thermal and dilatational residual stresses were modeled. Stresses from externally applied loads preferentially concentrate in the stiffer diamond phase. Thermal residual stresses strengthen the stiffer and weaker diamond phase through residual compression and weaken the carbide phase through residual tension. The dilatational residual stresses partially counteract the thermal residual stresses. Without thermal residual stresses the composite would have lower strength due to premature failure in the diamond phase. Without dilatational residual stresses the composite would have lower strength due to premature failure in the carbide phase. The strengths predicted by the enhanced models match the measured strengths quite well, despite significant uncertainty in the material properties and process parameters. |
