Effect of gradation by reactive imbibition on commercial WC-Co drilling tools used in oil and gas industries
Résumé
Cemented carbides are used in rock drilling for mining tools and wear resistant parts. These composite materials possess an excellent compromise between hardness and toughness. Nowadays, the concept of graded structure is widely studied to improve these two properties simultaneously, and thus to increase the service life of drilling tools. A continuous composition gradient on several millimeters is generated in commercial WC-Co drilling tools by using reactive imbibition method. The effects of this process are analysed in terms of microhardness, cobalt concentration and WC grain size. A continuous gradient of about 300HV on 8mm-height substrate for PDC cutters is obtained by in one-step imbibition process into combination with a boron-rich coating deposed on its free surface. This gradient is preserved and sometimes improved after HPHT (high pressure-high temperature) process that is used for the diamond table deposition on the WC-Co substrate. The service life in abrasion of a graded PDC cutter could reach an improvement by 160% in comparison with a standard PDC cutter, tested in the same conditions. An improvement about 50% is obtained for the shock resistance.