Applications of sustainable techniques in machinability improvement of superalloys: a comprehensive review

Superalloys are high-performance advanced materials specifically suitable for industrial applications at high as well as sub-zero temperatures. They are widely used in manufacturing components exposed to harsh working environments for prolonged durations undergoing non-uniform strains. Most superalloys possess a face-centred cubic microstructure, enabling them to exhibit significant creep resistance, corrosion resistance and thermo-mechanical fatigue even at elevated temperatures. However, these properties result in increased heat generation, increased tool wear and poor surface integrity, rendering them difficult-to-machine materials. Initially, dry machining was adopted as a tool for sustainable machining, but a few inherent characteristics, like high heat generation and large cutting forces limit its scope in superalloys machining. Subsequently, flood cooling was introduced to eliminate these problems. However, this strategy had an adverse effect on the environment and worker's health. Thus, the need for an alternate cooling technique complying with sustainable principles becomes essential. This review article focuses on the prerequisites for sustainable machining in general and superalloys machinability in particular. A thorough literature survey has been carried out focusing on the superalloys and their sustainable machining. From the present survey, it can be concluded that sustainable techniques such as minimum quantity lubrication, nanoparticles-based cooling, cryogenic cooling and hybrid cooling; are considered to be the alternate choices for machining superalloys which not only improve the machinability of superalloys but are also economical and eco-friendly. In the end, it can be concluded that such sustainable machining techniques have an ever-growing and ever-lasting scope, specifically in machining high-strength materials like superalloys.