Influence of process parameters on the cutting performance of SiAlON ceramic tools during high-speed dry face milling of hardened Inconel 718

Abstract

Heat-resistant superalloys (HRSAs) exhibit excellent mechanical strength and structural stability at elevated temperatures. Hence, aerospace and power industries have consistently chosen nickel-based superalloys over the years for manufacturing hot-section components. However, poor machinability of these alloys has always been a challenge. This paper investigates the cutting performance of new-generation SiAlON ceramics under extreme conditions of dry high-speed face milling of hardened Inconel 718. Comprehensive characterization of the ceramic tool and its milling performance were conducted using instrumented micro/nano-mechanical indentations, tool life studies, optical 3D imaging, and SEM/EDS investigation of wear patterns. Also, experimental results were linked to the finite element analysis (FEA) of temperature and stress profiles. It is demonstrated that a few major factors govern the ceramic tool life under the outlined cutting conditions: (1) High temperature at the cutting edge exceeding 1250 °C. This temperature is close to the melting point of Inconel 718, and moreover, it is highly localized around the cutting edge-chip interface. (2) High resultant mechanical stress on the tool of around 5.8 GPa. (3) Thermal and mechanical fatigue loading due to the discontinuity of the milling process, combined with (4) intensive built-up edge formation caused by severe weldability of the softened workpiece to the tool. Combination of these phenomena results in a significant change in the machinability of the workpiece material after surpassing a certain limit of cutting speed. The cutting forces, tool wear, and chipping show a significant decline with increasing the speed high enough, which is attributed to the change in the material properties of the workpiece and dissolution of the hard particles within the Inconel microstructure.