Chip Formation Analysis in High Speed Machining of a Nickel Base Superalloy with Silicon Carbide Whisker-Reinforced Aluminia

High speed turning tests were performed on a heat resistant alloy (Inconel 718), using SiC (20%) whiskers reinforced ceramic tools. The main aims of these tests were the following: (1) mapping cutting speed-feed and machined volume in order to find a region free from tool breakage; (2) analysing tool wear and chip formation mechanisms; and (3) from the experimental results modelling analytically both chip formation processes and tool wear mechanism. Tool and chip were observed at the SEM and EDAX semiquantitative analyses were carried out to evaluate micro-welds on the chip and areas of welded or scattered material over the tool. Micro-hardness mapping was carried out on the longitudinal cross-section of the chips to monitor its dependence by process parameters. Variable wear mechanisms along the tool-chip contact length that were attributed to variations in plastic deformation energy were observed. There variations were analytically modelled in orthogonal cutting conditions. Longitudinal and tranverse shear planes into the chip were also observed. The causes and the mechanisms of wear, chip formation and the hardening of work material were deduced. The presence of whiskers pull out mechanisms due to temperature effects in the tool-chip interface were also observed.