ADVANCED COATED CERAMIC TOOLS FOR MACHINING SUPERALLOYS

The main limitation on the use of nickel-base superalloys, such as INC ONEL 718, is the difficulty in conventional-type machining. The use of high cutting speed to achieve both machining adiabatic conditions and high productivity is necessary for their applications. This non-conve ntional type machining results in a short life-span of tools, even for those expensive ceramic ones with reinforced SiC whiskers (SiCw) suit able for use at high cutting speeds. The aim of the paper is to presen t the results of a new idea proposed by the authors to obtain an incre ase in tool life at high cutting speed by minimizing the temperature e ffects on composite reinforcement mechanisms. The 20% SiC whiskers rei nforced Al2O3 tools were CrN and (Ti,Al)N coated using the PVD techniq ue, and comparative machining tests on INCONEL 718 were carried out us ing uncoated and coated tools. After machining, the tools were observe d with a scanning electron microscope (SEM), and EDAX (X-ray) semiquan titative analyses were performed. The behaviour of the CrN and (Ti,Al) N layers using various cutting conditions was analysed and different w ear mechanisms along the tool chip contact length were observed. The c ause and the mechanisms of wear were deduced and mathematic models lin king tool life with process parameters were suggested. (C) 1997 Elsevi er Science Ltd.