Tool life and workpiece surface integrity when turning an RR1000 nickel based superalloy

Following a brief review on the turning of nickel based superalloys, the paper evaluates the machinability and workpiece surface integrity of a powder metallurgy HIP-ed (PHIP) RR1000 alloy, involving two phases of turning experiments using TiN/Al2O3/Ti(C,N) coated carbide inserts. Based on a maximum flank wear criteria of 200 μm, tool life exceeded 40 minutes when operating at or below 100 m/min, however Taylor tool life curves were extremely steep. At a feed rate of 0.08 mm/rev, workpiece surface roughness was ~ 0.5 mm Ra. Tests at cutting speeds of 80 m/min or less with new tools showed the ‘best/acceptable’ surface integrity with no visible white layer or plucking and a maximum distorted layer of ~6 μm deep. In contrast the surfaces produced using worn tools at a cutting speed of 100 m/min showed a distorted layer of ~20 μm deep with evidence of surface laps and plucking to a depth of ~15 μm.