Tool wear and surface integrity in liquid nitrogen clean cutting of cobalt-based superalloy GH605 with AlTiN coated tools

Abstract

The tool wear is severe and the machined surface quality is low in dry cutting of cobalt-based superalloy. The traditional coolant is harmful to the environment and not in line with sustainable development. The liquid nitrogen (LN2) clean cutting of cobalt-based superalloy GH605 using AlTiN coated tools is proposed in this work. The tool wear mechanism and the machined surface integrity are investigated. The results show that, with the decrease of LN2 injection temperature, the sharp wear stage of the tool can be delayed. The injection temperature directly affects the tool life. Compared with dry cutting, the tool life is increased by 42.5% at LN2 injection of −190 °C. Under the lower liquid nitrogen condition, the coating peeling is reduced on the rake face. The decrease of LN2 injection temperature can effectively reduce the damaged area of the flank face and inhibit the oxidation wear. The injection temperature between −30 °C and −150 °C can significantly reduce the surface roughness. The minimum surface roughness value at the injection temperature of −90 °C is 0.486 μm, which is 39.4% lower than that at dry cutting condition. When the LN2 injection temperature is below −90 °C, the thickness of the white layer is less than half of that in dry cutting condition. The hardness of the machined surface is enhanced and the residual stress is reduced at injection temperature below −150 °C. This work demonstrates the possibility of improving the machinability of cobalt-based superalloy by optimizing the LN2 injection temperature.