Development of nanostructured nitride coating using a two-step reactive PVD approach on uncoated carbides for improving machinability of Nimonic 90

The inhomogeneity and droplet related defects of cathodic arc deposition and lower ion density of magnetron sputtering-based tool coatings are the challenges that lowers coating quality. The present study carries two types of tool coatings in which one set of cutting inserts are coated with single layer conventional cathodic arc evaporation while the other set is coated with bimodal coating (arc and sputtering). The bimodal coating utilises an arc current of 80 A for the adhesive base layer and sputtering current of 500 mA for the surface refinement layer. SEM micrographs and atomic force microscopy confirmed that the bimodal coating significantly reduced the droplet density as well as improved the surface uniformity of arc deposited coating (84.9% reduction in R_t value). XRD plots reveal the formation of the nanocrystalline cubic structure of TiN. The crystallite sizes were analysed by Scherrer equation which were 12.4 and 14.3 nm for single layer and bimodal coating respectively. The bimodal coating showed a 7.3% enhancement in nano-hardness confirmed its superior performance. During the end milling of Nimonic 90 under constant machining parameters of 75 m/min cutting speed, 100 mm/min feed, and 0.05 mm axial depth of cut under a 5 bar compressed air cutting environment, the bimodal coated tool reduced the cutting forces, surface roughness, and cutting temperature by 45.26%, 34.24%, and 25.93% respectively compared with cathodic arc coating. These findings highlight that combining arc evaporation with sputtering effectively enhances coating quality for advanced machining applications.