Comparative Investigation of Smooth Polycrystalline Diamond Films on Dental Burs by Chemical Vapor Deposition Htet Sein, Waqar Ahmed, Christopher Rego, Mark Jackson, and Riccardo Polini (Submitted November 4, 2005; in revised form December 23, 2005) Depositions of hot filament chemical vapor-deposited diamond on cobalt-cemented tungsten carbide (WC- Co) rotary cutting dental burs are presented. Conventional dental tools made of sintered polycrystalline diamond have a number of problems associated with the heterogeneity of the crystallite, decreased cutting efficiency, and short life. A preferential (111) faceted diamond was obtained after 15 h of deposition at a growth rate of 1.1 μm/h. Diamond-coated WC-Co dental burs and conventional sintered burs are mainly used in turning, milling, and drilling operations for machining metal ceramic hard alloys such as CoCr, composite teeth, and aluminum alloy in the dental laboratory. The influence of structure, the mechanical characteristics of both diamond grains and hard alloys on the wear behavior, as well as the regimen of grinding on diamond wear are considered. Erosion wear properties are also investigated under air-sand erosion testing. After machining with excessive cutting performance, calculations can be made on flank and crater wear areas. Diamond-coated WC-Co dental burs offered significantly better erosion and wear resistance compared with uncoated WC-Co tools and sintered burs. Keywords cutting tool, diamond, HFCVD, wear 1. Introduction Diamond films are of interest for tribological applications due to their high hardness, low friction coefficient, high wear resistance, and chemical inertness (Ref 1). Diamond coatings are used in cutting tools and biomedical applications. At the present time, the most widely used dental diamond burs are manufactured by imbedding diamond particles into a metal matrix using a suitable binder containing nickel ions. Those burs have several limitations that are mainly due to the hetero- geneity of diamond crystallites, the contamination of oral tis- sue, and the variation in the product performance. There is no universal specification of the diamond particle sizes imbedded into the binder matrix to ensure a repeatable and consistent cutting performance. Recently, chemical vapor deposition (CVD) has been used for the fabrication of new dental burs (Ref 2), with continuous diamond film offering improvement in cutting efficiency and a longer life. Much of the work on the CVD of diamond has been carried out on flat substrates. Al- though cutting tools such as drills and inserts have been suc- cessfully coated with diamond-based coatings, there have been only a few reports of diamond deposition onto rotary cutting tools, such as cylindrical abrasive pencils and small spiral drills (Ref 3). In this study, the authors report the deposition of uniform diamond films onto the cutting edges of Co-cemented WC-Co dental burs that are used in the dental laboratory and in clinical surgery using a modified hot-filament CVD (HFCVD) system. The filament is mounted in a vertical arrangement with the dental bur held concentrically in between the filament coils, as opposed to the horizontal position commonly used in the HFCVD system configurations. This new vertical filament ar- rangement used in the modified HFCVD system enhances the thermal distribution and ensures uniform diamond coating (Ref 4). In this article, the results are reported of the investi- gation on diamond films deposited on WC-Co dental burs and microtools using an HFCVD system and the subsequent ma- chining results on extracted human teeth, CoCr hard metal alloys, borosilicate glass, and porcelain teeth. The Co- cemented dental burs operate at high cutting speeds in the range of 3,000 to 300,000 rpm (Ref 5). Such high operating speeds impose stringent demands on the cutting surfaces and the coating. The coating is required to be tough, adherent, hard, and wear-resistant to enhance the overall tool performance and extend the lifetime of the tool. 2. Experimental 2.1 Substrate Preparation The dental bur (WC-6wt.%Co) was 20 to 30 mm in length and 1 to 1.5 mm in diameter. Prior to diamond deposition, the dental burs were ultrasonically cleaned in acetone for 10 min to remove any surface impurities. The poor adhesion of deposited diamond films onto cemented WC surfaces can lead to cata- strophic film failure in metal cutting due to the presence of the Co binder (Ref 6). The Co binder suppresses diamond nucle- This paper was presented at the fourth International Surface Engineer- ing Congress and Exposition held August 1-3, 2005 in St. Paul, MN. Htet Sein, Waqar Ahmed, and Christopher Rego, Department of Chemistry and Materials, Manchester Metropolitan University, Chester St., Manchester M1 5GD, U.K.; Mark Jackson, Department of Mechanical Engineering, Purdue University, West Lafayette, IN 47907; and Riccardo Polini, Dipartimento di Scienze e Tecnologie Chimiche, Universita’ di Roma “Tor Vergata” Via Della Ricerca Sci- entifica, 00133 Rome, Italy. Contact e-mail: jacksomj@purdue.edu. JMEPEG (2006) 15:195-200 ©ASM International DOI: 10.1361/105994906X95878 1059-9495/$19.00 Journal of Materials Engineering and Performance Volume 15(2) April 2006—195