Developing diamond MMCs to improve durability in aggressive abrasive conditions

Abstract

Metal Matrix Composites (MMCs) are seeing increased use in tribological applications where hardness, toughness and wear resistance are required. Offshore drilling tools are such an application. They are subjected to wear and corrosion processes, which can occur simultaneously. Having already demonstrated the feasibility of including diamond as the hard phase in MMCs through thermal spraying [Surf. Eng., submitted for publication], this paper focuses on durability issues relating to the coatings. Synthetic, coated and uncoated diamond grits were used in conjunction with nickel-based hard facing powders as a matrix, to produce composite coatings. The coatings were then investigated in terms of their microstructure (light microscope, Scanning Electron Microscope (SEM)), their elemental composition using EDX and XRD to identify retention of diamond and phases in the coatings, their hardness and their resistance to dry abrasive wear. Preliminary results show that it is possible to produce a hard facing diamond composite coating with good distribution of the diamond phase and little degradation of the diamond during the spraying. The coatings show some limitations in terms of their quality and homogeneity but the work presented in this paper demonstrates that diamond MMCs (DMMCs), produced by thermal spraying, offer potential as durable coatings.