Machinability of nickel-based high temperature alloys

Nickel-based high temperature alloys have excellent physical properties, which make them ideal for use in the manufacture of aerospace components. However, they exhibit poor machinability. Though conventional machining in industries is currently being carried out using carbide tools, there is little scope for improving the material removal rate. Machining, being a major operation, needs to be improved in order to reduce the throughput time. High Speed Machining (HSM) is a promising technique for increasing productivity in this regard. This paper mostly reviews research and development work in the machining of nickel-based high temperature alloys carried out over the last 15 years with the objective of assessing the present scenario. Emphasis is laid on Inconel 718, which is most commonly used. Both turning and milling operations using conventional and High Speed (HS) machining are reviewed herein. HSM is discussed at length in comparison with conventional machining, as it is possible to drastically improve material removal rate using HSM. In addition to the study of insert materials and tool geometry, other aspects affecting HSM are also discussed. Surface integrity of Inconel 718 obtained through HSM and the recently developed technique of Plasma Enhanced Machining (PEM) is also addressed.