ARCI Develops Advanced Coatings for Superalloy Machining
Scientists from the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, an autonomous R&D Centre of the Department of Science and Technology, have developed two nanocomposite protective coatings—Titanium Aluminium Silicon Nitride (TiAlSiN) and Chromium Aluminium Silicon Nitride (CrAlSiN)—to improve the durability of tungsten carbide cutting tools used for machining nickel-based superalloys. These superalloys, including Inconel 718 (IN718), IN625 and IN617, are indispensable for components operating under extreme conditions in aerospace, energy and petrochemical sectors but present major manufacturing challenges due to their exceptional strength, hardness, rapid work hardening, poor thermal conductivity and strong chemical interaction with cutting tools.
The coatings were deposited in-house using cathodic-arc physical vapour deposition and evaluated for performance in milling operations. The research revealed that coating effectiveness depends significantly on the chemistry of the material being machined, with no single coating performing best for every superalloy. For IN718, the TiAlSiN-coated tool improved tool life by about 80% compared with an uncoated tool, while for IN625, the improvement was about 60%. For IN617, however, CrAlSiN proved remarkably superior, increasing tool life by more than 200%.
The study examined failure mechanisms, identifying that a major cause of damage was repeated adhesion of workpiece material to the tool surface, where a layer of the superalloy sticks to the cutting edge and breaks away, pulling tiny fragments from the tool and causing progressive chipping. The coatings helped delay this damage, with chipping and progressive wear identified as the major failure modes, while abrasion, adhesion and attrition contributed to the overall wear process.
Researchers also analyzed metal chips generated during machining, which exhibited characteristic shear bands and serrated or saw-tooth patterns reflecting intense thermo-mechanical conditions during cutting. The degree of chip segmentation was related to tool performance, providing further insight into the complex machining behavior of these advanced alloys.
The research, carried out at ARCI's Centre for Engineered Coatings and published in the journal Materials Today Communications, demonstrates that longer-lasting cutting tools can reduce downtime, improve productivity and lower the cost of machining high-value engineering components. More significantly, the study provides a scientific basis for selecting coatings according to the specific alloy being machined, enabling manufacturers to adopt a science-based, application-specific approach to protective coatings rather than seeking a universally superior solution.