Machining performance of hard-brittle materials by multi-layer micro-nano crystalline diamond coated tools

Abstract

Single layer diamond coatings, deposited on cobalt cemented tungsten carbide (WC-Co), with CH4 concentrations of 1%, 3% and 5% were prepared, by hot filament chemical vapor deposition (HFCVD). Moreover, according to the characteristics of different kinds of diamond structure, observed on the single layer coatings, multi-layer crystalline diamond films with micro-nano structures (composed of the 1% and 5%-type coatings) were prepared. The objective was to cumulate the increased interfacial adhesion and mechanical properties of each single layer diamond coating, into one multilayer coating, capable of resisting the efforts present between a milling tool and a hard-brittle material (natural marble). The coating morphology, structure, and resistance to crack propagation of the diamond films were evaluated. Furthermore, cutting tests with diamond-coated tools were performed, while observing the machining life and wear mechanism, on a hard-brittle material (marble). The results on the single layers showed that with the increase of the concentration of CH4, the adhesion to the WC-Co substrate, as well as the resistance to crack propagation is decreasing. The multilayer coating structure shows benefits from the single layer coatings, i.e. improved adhesion to the substrate and inhibition of crack propagation, while the tool life and machining stability are significantly better than the single diamond layer coated tools.