Modes of tool deterioration during milling of 718Plus superalloy using cemented tungsten carbide tools

Understanding the detailed progression of cutting tool deterioration is important in order to improve the milling of Ni-based superalloys. Therefore, a series of documented experiments have been conducted on alloy 718Plus using cemented carbide (WC–Co) tools. It has been observed that the commonly recognised build up layer in the initial stage does not significantly affect the tool deterioration process. Instead, from the beginning of milling, cutting forces/stresses could cause small chipping locally in the initially sharp cutting edge. Fracturing locally with cracks propagating outside the cutting edge along the flank face in the subsurface region could also take place and was consistent with the direction of the cutting force. There was an initial period of time during which a number of microcracks had initiated in and near the cutting edge on the rake face side. These cracks soon propagated resulting in extensively fracturing and blunting of the tool. Coating of the tools had provided little protection as in the cutting edge area the coating had broken away soon after milling started. The major tool failure mode was Co binder material having heavily deformed to fracture, separating the WC grains. Loss of strength in binder material at cutting temperatures is discussed.