From Micro to Nanometric Grain Size CVD Diamond Tools
CVD diamond coated tools are developed for applications as different as turning of cemented carbides and bone drilling. The diamond films are deposited by Hot Filament Chemical Vapor Deposition (HFCVD) with grain sizes varying from conventional micrometric (12 urn) to nanometric 100 nm) and film thickness up to 50 jam. Silicon nitride (Si3N4) ceramics are chosen for the base material in order to guarantee maximal adhesion. Both the micrometric and nanometric CVD diamond grades endure the cemented carbide turning showing slight cratering, having flank wear as the main wear mode. However, nanocrystalline diamond present the best behavior regarding cutting forces <150 N) and tool wear (KM=30 urn, KT=2 um and VB=110 urn) and workpiece surface finishing (Ra=0.2 um) In the case of the dental drilling experiments, a polymeric laminated test block is used to simulate the human mandible and maxilla. The temperature rise during drilling is monitored to prevent overheating above 42 47 degC that is known to cause tissue death and implant failure. It is possible to drill with a CVD diamond SisN4 coated tool with significantly lower forces (fourfold smaller) lower rise in temperature (4degC less) lower spindle speeds (100 rpm) and higher infeed rates (30 mm/min) when compared to the commercial steel (AISI420) drill bits.