Dry machining of silicon-aluminium alloys with CVD diamond brazed and directly coated Si3N4 ceramic tools

Silicon-aluminium alloys (Al-Si), with Si contents up to 20%, are important materials in automotive and aeronautical industries due to their low density and high wear resistance. The turning of these alloys has been done mainly by superhard tools like polycrystalline diamond (PCD). CVD diamond either as thin coatings on silicon nitride ceramics or as thick brazed tips on hard metals is alternative material. In this work, CVD diamond thin films were grown on Si3N4 ceramic substrates and thick CVD diamond plates were brazed onto WC-Co tools. These different inserts were used in dry turning of silicon-aluminium alloys with 12 wt% and 18 wt% Si. Both directly diamond coated and brazed tools are able to machine the Al-12 wt% Si alloy with negligible wear. In turning of Al-18 wt% Si, sharp edged tools yield lower cutting forces than the chamfered ones, with the occurrence of tool failure at about 500 and 100 m, respectively. CVD brazed tools proved to be able for dry turning this hypereutectic alloy, keeping the cutting forces below 60 N. Minimal wear was observed after 1500 m of cutting length, mainly caused by diamond chipping at the flank face.