Machinability of Inconel 718: A critical review on the impact of cutting temperatures

The demand for high temperature-resistant superalloys such as Inconel 718 is increasing rapidly, as they possess superior mechanical, chemical, and physical properties. Hence, these materials are highly adaptable for aerospace, nuclear, and marine applications. Nonetheless, during machining of such alloys, high temperatures develop at the interface region. It accelerates the tool wear and adversely affects the integrity of the prepared surfaces. Although conventional metalworking fluids are competent in normalizing/limiting the cutting-edge temperature, the environmental obligations and health issues to the workers have forced the manufacturing industry to move towards environment-friendly machining process, viz. dry machining. High-speed machining of Inconel 718 (under dry condition) can lead to the attainment of high cutting temperatures, thereby activating the mechanisms of built-up-edge (BUE) development and diffusion, leading to enhanced wear rate of tool. Besides, high temperatures can alter the integrity, infuse residual stresses, and promote crack generation/propagation on the processed surface. Therefore, the present paper contributes a detailed insight into heat generation during machining of Inconel 718 and its influence on various machining responses. Additionally, the work addresses multiple possibilities to reduce the cutting temperature with due emphasis on distinct machining methodologies, viz. dry, wet, and tool texturing.Abbreviations: BUE: Built-up Edge; AISI: American Iron and Steel Institute; AJM: Abrasive Jet Machining; AlTiN: Aluminium Titanium Nitride; Al2O3: Aluminum Oxide or Alumina; Al2O3/SiC: SiC whisker-reinforced alumina Al2O3 ceramic; Al2O3-TiC: TiC added alumina ceramic; AS: Conventional tool; AT-PA: Parallel grooves; AT-PE: Perpendicular grooves; AT-W: Wavy pattern; CaF2: Calcium fluoride; CBN: Cubic boron nitride; CBN-OR: Perpendicular to cutting edge; CBN-ORE : Perpendicular grooves 30 µm away from main cutting edge; CBN-PA: Parallel to cutting edge; CFT: Nano textured tool; CFT WS: Nano textured with soft coated WS2; CrN: Chromium Nitride; CT: Conventional cutting tool; DOC notch wear: Depth-of-cut notch wear; EBSD: Electron back scatter diffraction; ECM: Electrochemical machining; FCC: Face centered cubic; GWP: Global warming potential; HPC: High-pressure cooling; HPJ: High-pressure jet; HPJA: High-pressure jet assistance; HRSA: Heat-resisted super alloy; HSS: High-speed steel; IPF: Inverse pole figure; ISO: International organization for standardization; l/h: liter/hour; L/min: Liter/minute; Micro-EDM: Micro-electrical machining; MoS2: Molybdenum disulfide; MQL: Minimum quantity lubrication; MWFs: Metal-working fluids; NIOSH: National Institute of Occupational Safety and Health; PCBN: Polycrystalline Cubic Boron Nitride; PVD: Physical vapor deposition; SEM: Scanning electron microscope; Si3N4: Silicon nitride; ST: Graphite soft-coated tool; STT-F: Linear grooves on the flank surface; STT-R: Elliptical textures on the rake face; STT-0: Plain WC/Co carbide tool; STT-1: Elliptical grooves; STT-2: Parallel grooves; STT-3: Perpendicular grooves; TiAlN: Titanium Aluminium Nitride; TiCN: Titanium Carbonitride; TiN: Titanium Nitride; T-IPA: Perpendicular textures to chip flow; T-IPE: Parallel textures to the chip flow; T-PA: Texture surfaces inclined an angle to the chip flow; TT: Textured tool under dry condition; TT+SL: Textured tool under solid lubricant-assisted MQL cooling conditions; T1: Un-textured tool; T2: Texture tool having circular pit holes; T3: Hybrid texture tool combination of circular pit holes and linear grooves; TT: Textured inserts; TT: WS2-soft-coated WS2 textured tool; T1: Conventional insert; T2: Conical dimple-textured tool; T3: Square dimple-shaped insert; T4: Scratches provided on the cutting insert; T-1: Untextured insert; T-2: Pit holes textured insert; T-3: Hybrid textured insert; US: United States; USM: Ultrasonic Machining; WC: Tungsten carbide; WC–Co: Tungsten carbide-cobalt; WEDM: Wire electrical discharge machining; WS2: Tungsten disulfide