The machinability of nickel-based alloys: a review

Abstract

This paper presents a detailed review of the various types of nickel-based alloys available on a commercial basis and their development including alloying additions as well as processing techniques employed to achieve specific mechanical and/or chemical properties. Problems associated with the machining of nickel-based alloys as well as tool wear and the mechanisms responsible for tool failure are identified and discussed. The integrity of the machined surfaces and tool life are the most important considerations during machining. These and other factors governing the machinability of nickel-based alloys are mainly affected by notching of the cutting tool, primarily at the depth of cut region, as well as by flank wear and insert chipping/fracture; and by failure modes caused singly or jointly by diffusion, attrition, and abrasion wear mechanisms in addition to mechanical and thermal fatigue loading of the cutting tools. Most of the failure modes can be minimised when machining in the presence of coolants and in an oxygen-rich environment. The use of a high pressure coolant supply, despite improved chip segmentation and machining in the presence of argon and nitrogen-rich environments, tend to accelerate tool wear rate leading to lower tool life. Improvements in tool performance can be achieved with an increase in the included angle and/or the nose angle of cutting tools due to the increased edge strength and tool–chip contact area plus a reduction in the approach angle. Recently developed cutting tool materials such as mixed oxide, SiC whisker reinforced alumina ceramics, sialon and multi-layer coated cemented carbide cutting tool material have all exhibited the capability to machine nickel-based alloys at higher speed conditions than those achieved with conventional cemented carbide tools.