On the perfoemance of a CRN coated SIC whiskers reinforced ceramic tool high speed machining of NI-base super-alloys.

The main limitation on the wider use of Nickel-base super-alloys, such as INCONEL 718 (UNS N07718) is the difficulty in conventional-type machining. Even the expensive SiC whiskers reinforced ceramic tools, that are more suitable for use at high cutting speeds, have a short life-time. The aims of the study is to obtain an increase in tool life by minimising the temperature effects on composite reinforcement mechanisms. 20% SiC whiskers reinforced Al2O3 tools were CrN coated by PVD. Comparative machining tests on INCONEL 718 were performed using 20% SiC whiskers reinforced Al2O3 tools and CrN coated 20% SiC whiskers reinforced Al2O3 ones. After 40 and 60×10-6 m3 alloy removal the tools were observed at SEM and EDAX semiquantitative analyses were carried out. The CrN layer behaviour under the various cutting conditions used was analysed. Different wear mechanisms along tool chip contact length were observed. The causes and the mechanisms of wear were deduced and a mathematics model linking tool life with process parameters is suggested.