Effects of Coating Materials on the Machinability of a Nickel Base,C-263, Alloy

PVD coated (TiN/TiCN/TiN, TiAIN and TiZrN) and uncoated carbide tools were used to machine a nickel base, C-263, alloy at high-speed conditions. The test results show that the multiple TiN/TiCN/TiN coated inserts gave the best overall performance in terms of tool life when machining at cutting speeds up to 68 m min and at depths of cut of 0.635 mm, 1.25 mm and 2.54 mm. All the tool grades tested gave fairly uniform surface roughness (Ra) values, below the rejection criterion, at lower speed conditions. The TiZrN coated inserts gave the lowest component forces when machining at lower cutting speed conditions while the TiA/N coated inserts gave the lowest component forces when machining at a higher speed of 68 m min^?1 and depth of cut of 1.25 mm. This tool performance can generally be attributed to the difference in their ability to provide effective lubrication at the cutting zone, thermal conductivity of the coating materials as well as the cutting conditions employed. The uncoated carbide tools generally encountered more severe crater wear, chipping/fracture of the cutting edges as well as pronounced notching during machining. This is due to their inability to provide effective lubrication at the cutting zone, thus impeding the gliding motion of the chips along the rake and flank faces respectively, thus accelerating flank wear. Analysis of the worn tool edges revealed adhesion of a compact “fin-shaped” structure of hardened burrs with saw-tooth like edges. This generally alters the initial geometry of the cutting edge, consequently resulting to poor surface finish with prolonged machining.