Wear behaviour of uncoated and diamond coated Si3N4 tools under severe turning conditions

Ceramic tools with and without diamond coating were used as cutting material in continuous and dry turning operations of DIN GG25 grey cast iron. Nine combinations of speed (500, 600 and 900 m min−1) and feed (0.1, 0.25 and 0.4 mm rev−1) were used keeping the depth-of-cut constant and equal to 1 mm. The results show that the wear processes taking place in the tool tips of the ceramic inserts, in all cutting conditions, were both mechanical and chemical. The former was due to abrasion and adhesion, and the latter to a diffusion mechanism. However, this phenomenon was more obvious in the diamond coated inserts. A dynamometer and a data acquisition system were used to measure and record the cutting force developed during the turning tests. The worn cutting edges and rake surfaces were analysed by scanning electron microscopy (SEM) and the flank wear was measured by optical microscopy. The analysis of flank wear revealed that the tool life of diamond coated inserts is longer than that of the uncoated inserts.