Cutting performance and wear mechanisms of Sialon-Si3N4 graded nano-composite ceramic cutting tools

Sialon-Si3N4 graded nano-composite ceramic tool materials were fabricated by using hot-pressing technique. The residual stresses in the surface layer of the graded ceramic tool materials were calculated by the indentation method. The cutting performance and wear mechanisms of the graded tools were investigated via turning of Inconel 718 alloy in comparison with common reference tools. The surface roughness of the finish hard turning of Inconel 718 and the microstructures of the chips were also examined. Worn and fractured surfaces of the cutting tools were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that graded structure in Sialon-Si3N4 graded ceramic tool materials can induce residual compressive stresses in the surface layer during fabrication process. Tool lifetime of graded ceramic tool was higher than that of the common reference tool. The longer tool life of the graded nano-composite ceramic tool was attributed to its synergistic strengthening and toughening mechanisms induced by the optimum graded compositional structure of the tool and the addition of nano-sized particles. Wear mechanisms identified in the machining tests involved adhesive wear and abrasive wear. The mechanisms responsible for the higher tool life were determined to be the formation of compressive residual stress in the surface layer of the graded tools, which led to an increase in the resistance to fracture.