Abstract
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 min 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 μm 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.
Highlights
The ability to maintain much of their strength/integrity and resist corrosion at elevated temperatures are key characteristics of nickel-based superalloys and the reason for their extensive use in gas turbine engines for combustion and turbine components [1,2,3]
Other recommendations were that feed rate should range from 0.05 to 0.3 mm/rev depending on the required workpiece surface roughness and that depth of cut should be 0.3 to 0.5 mm when finishing
The current study aims to complement this work by providing in-depth analysis of the surface integrity of a powder metallurgy hot isostatic pressing (HIP)-ed (PHIP) RR1000 alloy after turning, which has relevance for the production of components such as casings and discs in gas turbine aero engines
Summary
The ability to maintain much of their strength/integrity and resist corrosion at elevated temperatures (up to ~ 1000 °C) are key characteristics of nickel-based superalloys and the reason for their extensive use in gas turbine engines for combustion and turbine components [1,2,3]. Analysis of the chemical and mechanical properties of RR1000, suggest that it has even lower machinability than current disc alloys including Inconel, Waspaloy or Udimet products [12, 23] and that the operating window for cutting parameters to achieve acceptable tool life, surface roughness and integrity is very narrow This is due in part to high levels of redeposited material which are found at higher material removal rates or when using cutting inserts with a smaller nose radii. Tool life would be expected to be long (~ 100 min plus) and due to insufficient time and workpiece material, life trials were not performed; only surfaces produced with new tools were evaluated In both phases of work, the depth of cut was held constant at 0.25 mm to represent finishing conditions, as any component would be produced near net shape eliminating the requirement for extensive roughing operations. Component application and the requirement for desirable surface integrity [2]
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