Electro-Spark Coating of High Entropy Alloys on AISI 410 Stainless Steel Substrates to Improve the Surface Properties and Wear Resistance

Chandrakant, Chandrakant and Panigrahi, Bharat Bhooshan (2019) Electro-Spark Coating of High Entropy Alloys on AISI 410 Stainless Steel Substrates to Improve the Surface Properties and Wear Resistance. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

High-entropy alloys (HEAs) are new class of solid solution alloys that have attracted worldwide attention due to excellent properties. These alloys can be used as a bulk material of its own or strengthening of other materials as a reinforcement, such as composites. Since these alloys exhibit very high strength, considerably good hardness and very good resistant to oxidation and corrosion. Therefore, there is huge scope for using these alloys for surface strengthening and hardening and modifications of surface properties of other alloys and steels. This has been a major motivation for the present work to explore the possibility of this alloy for such applications. A large variety of commercial processes are available for variety of coatings using powders. Among these, an electro-spark coating (ESC) is an emerging technology with promising features. In this process, a controlled electric spark is generated between two surfaces, one to be a substrate and another to be the coating material. Feed (Coating material) is usually in the form of thin rod or filament. A major advantage of this process is, its low cost compared to other available techniques and can be employed for variety of alloys including low melting alloys to high melting point alloys such as tungsten or tungsten carbides etc. It can also be used for selective repairing of defects and cracks of the surface of the component. In general, coating behaviors of HEAs have not been well studied particularly coating through ESC. Objective of the present investigation is to study the coating behavior of AlCoCrFeNi and CoCrFeNiMn equiatomic high entropy alloys on a steel substrate (AISI 410 SS) and its effect on surface hardening and wear properties of the substrate. Alloys powders were prepared through mechanical alloying and vacuum hot pressed to produce high density components. Thin rods (filament) of about cross-section of 3mm x3mm were prepared from the sintered specimen. Filament was about 50 to 60 mm long. There are several aspects, which are being studied currently, namely, phase stability and phase evolution of coated alloy, whether the alloy has same phase composition after coating to that of initial phase of the filament or not. Properties of post coated surface are being currently studied, such as bonding, diffusion depth, hardness and wear and vi tribological properties etc. It was found that surface hardness has improved significantly after coating. Among the HEA, AlCoCrFeNi coating resulted relatively higher hardness compared to the coating of CoCrFeNiMn HEA. Wear rate has dropped significantly after coating of HEA compared to un-coated steel. In this case also, AlCoCrFeNi coating shows better wear resistance compared to CoCrFeNiMn HEA. The preliminary observation suggests, the ESC process could be a promising method and HEA alloys could be the good materials for improvement of surface properties of steels and alloys.

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