Development, properties, applications and machinability of superalloy Inconel

Abstract

Ni-based alloys contain Cr, Mo, Fe, Cu, Al, Ti, Co etc. as alloying elements and possess unique and versatile mechanical and chemical properties. So, these alloys are widely used for different impact-resistant and high-temperature applications such as aircraft engines, gas and steam turbines, pumps, rocket motors, nuclear reactors and petrochemical industries, etc. However, conventional machining of these high-temperature superalloys are cumbersome as they cause tool blunting, unusual and rapid tool wear, work-hardening, chatter vibration and high cutting temperatures and so on, which result in cutting instability and poor machinability. This study provides an overview on development, properties and applications of Ni-based high temperature alloys (HTAs). Then, it presents a review of research findings on machinability of these superalloys while applied conventional turning (CT), conventional milling (CM), high speed machining (HSM), hybrid machining and ultrasonic vibration cutting (UVC) techniques using mainly coated and uncoated carbide, cermets, ceramics, Sialons, SiC WRA (whisker reinforced alumina) and CBN (cubic boron nitride) tools. It has been observed that the properties of Ni-based superalloys not only depend on various alloying elements but also on their percentages and combinations, microstructures, strengthening mechanisms and heat treatment procedures during formation of metallic structure or phase(s). Among the Ni-based HTAs, Inconel 718 is most widely applied and thereby it has drawn much attention by the researchers and manufacturers. It has also been observed that carbide tools are frequently used to machine the Ni-based HTAs as they are comparatively inexpensive. However, the CBN tools perform always better than the carbide tools in all aspects. The HSM method offers higher productivity than the other methods but it requires special machining arrangements, while the UVC technique offers better surface finish (e.g. < 1 μm Ra) and longer tool life but lower productivity. At higher cutting speeds, the cutting tools chipped off or catastrophically failed in the UVC method. It has been observed through this study that the CT, CM, HSM, hybrid machining and UVC techniques can be applied for machining superalloy Inconel; however, cutting performances and productivity in each method depend on specific cutting conditions. © 2011 by Nova Science Publishers, Inc. All rights reserved.