New coatings to improve superalloy machining for aerospace and energy sectors

The advanced surface-engineering method developed by scientists could help improve the durability of cutting tools used in superalloy machining. According to a PIB report, this new discovery could prove extremely beneficial for the aerospace, energy, and petrochemical sectors. Nickel-based superalloys are indispensable in these sectors for manufacturing components that can operate in extremely harsh and diverse conditions.

Machining superalloys for use in aircraft engines, power plants, and petrochemical systems has been a major challenge in the manufacturing sector. Nickel-based superalloys such as Inconel 718 (IN718), IN625, and IN617 possess extraordinary strength and hardness, making them very difficult to cut or shape. During machining, these metals undergo rapid work hardening, have low thermal conductivity, and experience intense chemical interaction with cutting tools. These factors cause cutting tools to wear out quickly, resulting in decreased productivity and increased production costs.

Scientists at the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), based in Hyderabad, have worked to solve this problem. ARCI is an autonomous research and development centre under the Department of Science and Technology (DST). Scientists have developed and evaluated two new nanocomposite protective coatings on widely used tungsten carbide cutting tools. The names of these two coatings are Titanium Aluminium Silicon Nitride (TiAlSiN) and Chromium Aluminium Silicon Nitride (CrAlSiN).

These coatings were applied at the institute itself using the 'Cathodic-Arc Physical Vapor Deposition' technique. Through this method, scientists were able to evaluate the performance of these tools for the milling process of IN718, IN625, and IN617. This study tested not only the tool life but also the processes affecting the performance of the coating.

A very important finding has emerged in this research that no single type of coating can provide the best performance for every superalloy. The effectiveness of the protective coating depends heavily on the chemical composition of the metal being machined and the interaction of that metal with the coating. This discovery provides a scientific basis for manufacturers to select the appropriate coating according to the specific material.

Study results show that for IN718, a tool with TiAlSiN coating showed an improvement of about 80% in lifespan compared to a tool without coating. For IN625, this improvement was recorded at about 60%. However, for IN617, the performance of CrAlSiN coating was significantly superior, resulting in an increase of more than 200% in tool life. These results clarify that one coating may be more suitable for IN718 and IN625, while the other coating can perform much better for IN617.

Scientists also investigated how cutting tools fail. A major cause of damage to tools was the frequent sticking of the workpiece material to the tool surface. During machining, a layer of superalloy can stick to the cutting edge, and when that layer later breaks off, it pulls small pieces of the tool with it, causing the tool tips to gradually break (chipping). These protective coatings helped in delaying this type of damage and increasing tool life. Researchers identified chipping and progressive wear as the main types of tool failure, in which abrasion, adhesion, and attrition contribute to the overall wear process.

Scientists also observed the metal chips produced during machining. These chips showed specific shear bands and saw-tooth patterns, reflecting the intense thermo-mechanical conditions created during cutting. The degree of chip fragmentation was related to tool performance, providing more understanding about the complex machining behavior of these advanced alloys.

Using cutting tools that last longer can reduce machine downtime, increase productivity, and reduce the cost of machining high-engineering components. This study points towards a science-based and precise application-specific approach for protective coatings. Instead of searching for a single universal coating for every situation, manufacturers can now select or design coatings based on the specific composition and behavior of the alloy being machined. This will enable more efficient, reliable, and cheaper production of components made from advanced materials.

This research conducted at ARCI's Engineered Coatings Centre has been published in the journal 'Materials Today Communications'. This study proves that the key to improving the machining of the most challenging materials in industries lies not just in developing better coatings, but in selecting the right coating for the right material.

ARCI was an international advanced research centre for powder metallurgy and new materials, which was an autonomous research and development centre under the Department of Science and Technology, Government of India.