Faculty Publications
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Item Microstructural evolution and cyclic oxidation behavior of HVOF-sprayed NiCrSi and NiCrC coatings on T11 steel(Elsevier Inc., 2024) Medabalimi, S.; Hebbale, A.M.; Singh, R.; Desai, V.; Ramesh, M.R.This study analyzes NiCrSi and NiCrC coatings developed on low alloy ferritic stainless steel (grade T11) through the HVOF spraying technique. The coatings were characterized by their phase constitution, microstructure, cyclic oxidation behavior, and hardness. X-ray diffraction (XRD) analysis confirmed the presence of the NiCr solid solution matrix as the primary phase in both coatings. Moreover, the microstructure of the NiCrSi coating included the hard intermetallic compounds like Cr?Si and Ni?Si and the NiCrC coating contained the hard phases like Cr?C? and Ni?C which improved the hardness and the wear resistance of the coatings. Microhardness measurements revealed that the coatings had an average hardness of 300 ± 50 HV, significantly greater than the substrate hardness of 225 ± 25 HV. Cyclic oxidation tests were carried out at 700 °C revealed that both the coatings showed a lower weight gain than the uncoated substrate, suggesting enhanced oxidation resistance. This was because the protective oxide layers like Cr?O? and SiO? in the NiCrSi coating and Cr?O? and NiO in the NiCrC coating were formed. X-ray analysis establish ed. the presence of these oxides, which inhibited oxygen penetration through the coatings and provided additional protection against oxidation. Therefore, the study revealed that both NiCrSi and NiCrC coatings have good mechanical and oxidation resistance properties, which make them suitable for high-temperature applications where there is a need for improved durability, wear resistance, and protection against oxidation. © 2024Item Microstructure, Mechanical, and Dry Sliding Wear Performance of Equimolar CoCrNiTiMo and CoCrNiTiW High-Entropy Alloy Coatings(Springer, 2025) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.In the present investigation, mechanical alloyed CoCrNiTiMo and CoCrNiTiW equimolar HEA powders were employed as feedstock in the development of dense coatings using high-velocity oxy-fuel technique. The dry sliding wear behavior of uncoated substrate and high-entropy alloy (HEA) coatings were extensively investigated at different temperatures and loads using a pin-on-disk tribometer. The microstructures and phases of the mechanical alloyed powders, deposited coatings, and worn surfaces were thoroughly studied. The mechanical alloyed CoCrNiTiMo and CoCrNiTiW HEAs demonstrated the evolution of two BCC solid solutions. However, the deposited coatings reported the formation of additional phases, including Co3Ti intermetallic and NiTiO3 spinel. The microstructural analysis of CoCrNiTiMo and CoCrNiTiW coatings unveiled a compact lamellar structure characterized by robust mechanical interlocking to the substrate. The CoCrNiTiMo and CoCrNiTiW HEA coatings displayed porosities of 1.12 ± 0.05% and 1.39 ± 0.03%, respectively. Additionally, the microhardness assessments revealed superior values for CoCrNiTiMo and CoCrNiTiW HEA coatings, measuring at 927 ± 45 HV0.3 and 951 ± 38 HV0.3, correspondingly. The wear rate of CoCrNiTiMo HEA coating dropped by 70.5%, from 17.34 ± 2.8 × 10?6 mm3/N-m to 5.1 ± 1.6 × 10?6 mm3/N-m with an increment in the wear testing temperature from ambient to 600 °C. Concurrently, the CoCrNiTiW coating experienced a 76.3% drop in the wear rates from 15.8 ± 3.7 × 10?6 mm3/N-m to 3.73 ± 2.1 × 10?6 mm3/N-m. The significant fall in the wear rates at higher temperatures was accredited to the development of oxide tribofilms. CoCrNiTiMo exhibited discernible oxide phases, including CoMoO4, TiO2, and NiO. In contrast, its counterpart, CoCrNiTiW, generated WO3, CoWO4, and TiO2 oxides at a temperature of 600 °C. The adhesive wear at RT transitioned to predominant oxidative wear with slight fatigue and abrasive wear at high temperatures. © ASM International 2025.