Surface engineering of WC-Co used in dental tools technology

Abstract

Diamond films, deposited using chemical vapour deposition (CVD), were grown onto cemented tungsten carbide (WC-Co). The 'grade' of hard metal used in this study is commonly employed in dental tools, such as burrs and in microdrills. The WC-Co substrates consisted of 10% cobalt and ≤1 μm WC grain size. Critical to the formation of well bonded diamond layers is the initial nucleation process, which is highly dependent on WC grain size and cobalt concentration. It is shown that by appropriate surface treatment and process optimisation it is possible to grow good quality diamond films onto WC-Co used in dental tools. The as grown films were polycrystalline in nature and consisted of compressive stresses, which were measured using the Raman spectroscopy technique. Indentation test methods were used to characterise the coating adhesion. Two independent indentations were performed at 300 and 500 N loads on diamond coated samples. The different responses of the coatings to the indentations at the two loads are discussed. Coated WC-Co dental burrs were tested using drilling tests on extracted human teeth for performance. The polydiamond crystals deposited onto the burr remained completely intact on the dental tool even after drilling 500 holes into human teeth. However, conventional diamond burr results revealed that the majority of the imbedded diamond particles had been dislodged from their cavities after drilling 500 holes.