Improvement of cutting performance of high x value α/β-SiAlON ceramic cutting inserts via tailoring microstructure and oxidation behavior

Abstract

Despite the well performance of SiAlON ceramic cutting tools in machining nickel-based superalloys, there is still the problem of rapid wear due to high cutting temperatures and high cutting forces. In this study, novel high x value Y-α/β-SiAlON ceramic cutting inserts were fabricated by microwave sintering. The microstructure and oxidation behavior were tailored by varying the designed α/(α + β) ratios to enhance the cutting performance. The oxidation behavior was studied by static oxidation tests at 1000–1400 °C in air, and the cutting performance was tested by milling Inconel 718 superalloys. The results indicated that increasing α/(α + β) ratio under high x value composition could promote the elongation of α-SiAlON grains thus improving the mechanical properties. However, this also increased the volume of intergranular phase (IGP), which gradually weakened the oxidation resistance. At temperature above 1200 °C, the oxidation of IGP was much faster than α’ and β’ phases. This resulted in the decline of surface hardness and grain boundary strength, which in turn affected the cutting performance. When controlling the designed α/(α + β) ratio to 50%, a balance was achieved between the microstructure and oxidation resistance that the tool life was promoted.