Multilayer CVD Diamond Coatings in the Machining of an Al6061-15 Vol % Al2O3 Composite

Ceramic cutting inserts coated with ten-fold alternating micro- and nanocrystalline diamond (MCD/NCD) layers grown by hot filament chemical vapor deposition (CVD) were tested in the machining of an Al based metallic matrix composite (MMC) containing 15 vol % Al2O3 particles. Inserts with total coating thicknesses of approximately 12 µm and 24 µm were produced and used in turning: cutting speed (v) of 250 to 1000 m·min−1; depth of cut (DOC) from 0.5 to 3 mm and feed (f) between 0.1 and 0.4 mm·rev−1. The main cutting force increases linearly with DOC (ca. 294 N per mm) and with feed (ca. 640 N per mm·rev−1). The thicker coatings work within the following limits: DOC up to 1.5 mm and maximum speeds of 750 m·min−1 for feeds up to 0.4 mm·rev−1. Flank wear is predominant but crater wear is also observed due to the negative tool normal rake. Layer-by-layer wear of the tool rake, and not total delamination from the substrate, evidenced one of the advantages of using a multilayer design. The MCD/NCD multilayer diamond coated indexable inserts have longer tool life than most CVD diamond systems and behave as well as most polycrystalline diamond (PCD) tools.