Development of sialon ceramics for the machining of superalloys and determination of cutting performance

Al2O3-SiCw cutting tools are widely Usel on turning applications of nickel-based superalloys, and exhibit superior performance compared to other ceramic cutting tools. SiAlON ceramics, particularly β-SiAlONs, have been used in the machining of superalloys, but there is a need to improve their performance further to compete with widely used Al2O3-SiCw composite, which is hazardous to health and costly. The aim of this thesis is to develop a SiAlON cutting tool with higher chemical stability, allowing for higher cutting speeds or longer cutting durations, and with a production cost lower than Al2O3-SiCw for the superalloy turning applications. In this work, β-SiAlON/12H polytype composite was studied to be developed by using various sintering additives, namely La2O3, Nd2O3, Sm2O3, Y2O3, and their combinations for superalloys, particularly Inconel 718, turning applications. It was found that fully dense β-SiAlON/12H polytype composite with a reasonable amount of the 12H phase was developed by using La2O3-Y2O3 as co-dopant and Nd2O3 or Sm2O3 as a single dopant. β-SiAlON/12H cutting tools have significantly less flank wear than a commercial β-SiAlON and quite comparable wear to Al2O3-SiCw, which is widely used in Inconel 718 turning. No significant differences in the cutting performance were observed between cutting tools made of β-SiAlON/12H obtained by using different dopants.