Faculty Publications
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Item High-Temperature Solid Particle Erosion Behavior of Partially Oxidized NiCrBSiFe/NiCr Plasma Spray Coatings(Springer, 2021) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.This paper investigated the solid particle erosion behavior of partially oxidized NiCrBSiFe and NiCr coatings by varying temperature and impact angle. The challenge in the current situation is to process a new system of powders containing metallic and oxide phases. Partially oxidized powders containing metallic and oxide phases were processed by flame spraying the alloy powders into distilled water and allowing the oxide layer to form while keeping the core in the middle of the particle. Partially oxidized coatings were developed on MDN321 steel using the plasma spray technique with feedstock of partially oxidized powders. An air jet erosion test was carried out using Al2O3 erodent of grit size 50 µm at room temperature, 200, 400, 600, and 800°C by varying 30, 45, 60, 75, and 90° impact angles. Coatings were characterized concerning bond strength, porosity, micro-hardness, and density. The effect of temperature and impact angle on volumetric erosion loss was studied using SEM, EDS, and XRD analysis. Partially oxidized NiCrBSiFe coating exhibited better erosion resistance compare with partially oxidized NiCr coating. NiCr coating demonstrates maximum volumetric erosion loss at 45° impact angle, whereas NiCrBSiFe at 60° impact angle under all tested temperatures. © 2021, ASM International.Item High-temperature wear and frictional behavior of partially oxidized Al with NiCr composite coating(Institute of Physics Publishing helen.craven@iop.org, 2019) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.The influence of composite coating in improving wear and frictional behavior from room temperature to 600 °C was investigated. Partially oxidized Al powder was prepared with a flame spray process by spraying pure Al powder into distilled water. The composite powder is the mixture of 30 weight percent of partially oxidized Al and 70 weight percent of NiCr alloy powder. The composite powder was subsequently coated on MDN321 steel by air plasma spray process. The composite coatings are characterized with respect to adhesion strength, porosity, micro-hardness, and density. Wear and frictional behavior of coatings are evaluated under disc speed of 1 and 2 m s-1, loads of 10, 20 and 30 N and 3000 m sliding distance. The test results indicated that at room temperature, frictional heat generated due to applied load produce three-body abrasion at the interface caused to increase the wear and friction in the coating. The oxide film formed at high temperature due to plastic deformation avoids surface degradation at the interface and reduce the wear and friction. The worn surfaces at 600 °C consist phases of ?-Al2O3, NiO, and Cr3O. These phases are contributing to improving the wear resistance of the coating more than 4-times compared to uncoated steels under varying load and sliding velocities. The coefficient of friction reduced with increase in temperature due to generated oxides act as lubricants at the interface. © 2019 IOP Publishing Ltd.Item Developing partially oxidized NiCr coatings using the combined flame spray and plasma spray process for improved wear behaviour at high temperature(Elsevier Ltd, 2021) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.The powders of NiCrBSiFe and NiCr are partially oxidized using a flame spray process and are deposited on MDN321 steel substrate using a plasma spray process. The effect of partial oxidization on microstructure, microhardness, density, bond strength, and porosity of the coatings is analyzed. The friction and wear behaviour of the coatings was assessed using a pin-on-disc tribometer by varying loads (10, 20 and 30 N), sliding velocities (1, 2 m/s) and temperatures (RT, 200, 400 and 600 °C). Worn surfaces of NiCrBSiFe and NiCr coatings consist of oxide phases of SiO2, NiO, Cr2O3 and NiCr2O4 at elevated temperatures. These phases contributed to reducing the wear rate by five folds in coated steels compared to uncoated steels at 600 °C. The wear rate in coating decreases with an increase in temperature. The coefficient of friction was reduced gradually with the temperature in coatings and substrate. The wear rate coefficient of NiCr coating was 1.7 times higher than the NiCrBSiFe coating. © 2021 Elsevier B.V.Item Evaluation of High Temperature Dry Sliding Wear Behaviour of Thermal Sprayed and Microwave Fused WC12Co and CeO2 Modified WC12Co Composite Coatings(Academic Enhancement Department, King Mongkut's University of Technology North Bangkok, 2023) Pradeep, P.D.; Venkataramaiah, V.C.; Shivegowda, N.H.; Medabalimi, S.R.Thermal spray methods are used to increase the wear resistance of working surfaces. Microwave post-treatment is the advanced approach for enhancing the properties of thermal spray coatings. The current investigation focuses on the wear behavior of HVOF-sprayed and microwave-treated coatings. The WC12Co and CeO2 modified WC12Co composite coatings were successfully deposited on AISI4140 steel using the HVOF thermal spray technique. The coatings were tested in both as-sprayed and microwave post-treatment conditions. The dry sliding wear tests were carried out at temperatures of RT, 200, 400, and 600 ℃ with various loads. Vickers hardness tester, Scanning Electron Microscopy (SEM), and X-ray diffraction (XRD) equipments were used to investigate the microhardness, microstructure, and phases of coatings, respectively. In both compositions, the microwave-fused coating had a fine homogeneous structure and higher hardness than the as-sprayed depositions. For typical loads of 20 N and 40 N for both compositions, the friction coefficient decreased with increasing temperature in the as-sprayed and fused coatings. At all conditions, the microwave fused coating outperforms the as-sprayed coating in terms of wear resistance. During sliding action, the fused coatings exhibit tribo-oxide layers, which provide the best wear resistance of the microwave fused composite coatings. The wear resistance of the WC12Co coatings is improved as compared to CeO2 modified WC12Co coatings. © 2022 King Mongkut’s University of Technology North Bangkok. All Rights Reserved.