Impact of intra-bond orbital hybridization and morphology of diamond coatings on machining performance of coated end mill cutters

The current study analyses machining performance of diamond coated end mills in the light of coating morphology, difference in intra-bond orbital hybridization, wettability and anti-frictional characteristics. Three different classes of diamond coatings, including a new generation nanocrystalline (NCD) coating, were chosen so that they do contain different intensity of sp2 and sp3 hybridisation in CC covalent bonding. The machining experiments were carried out in slot machining mode accomplished by two-fluted endmills and on aluminium and a silicon-free aluminium alloy, AA2024. sp2-rich hydrogenated DLC coating demonstrated outperformance in anti-frictional characteristics over its counter parts when tested against a sliding aluminium disc. The tribological performance of the sp3-rich NCD coating was superior to the sp3-hybridized microcrystalline diamond coating (MCD) but could not excel H-DLC coating. The difference in the hybridization level did not influence wettability towards the molten aluminium. However, the end mills having new generation NCD coating outperformed its counterparts at high speed machining conditions, establishing the supremacy over H-DLC coating, even over the MCD coating. The coating morphology including roughness played the most influencing role in favour of the machining performance, considering the ability to arrest built up layer (BUL) formation and to produce high surface finish of the machined work-surface.