Faculty Publications
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Item Clad developments through microwave hybrid heating technique processing and properties(CRC Press, 2022) Suresh, G.; Ramesh, M.R.; Hebbale, A.M.; Srinath, M.S.[No abstract available]Item Saltwater corrosion behaviour of equal channel angular pressed AZ80/91 Mg alloys(Elsevier Ltd, 2021) Hebbale, A.M.; Naik, G.M.; Badiger, R.I.; Bellubbi, S.; Patil, S.; Narendranath, S.In this study, AZ80/91 Mg alloys were used to comprehend the electrochemical corrosion behaviour of coarse-grained and fine-grained Mg alloys in different concentration of NaCl solution as well as in the marine environment. The inadequate studies of the corrosion response of ECAPed AZ80 and AZ91 Mg alloy in a different environment were noticed. Accordingly, the current research presents and compares the corrosion behaviour of AZ80/91 Mg alloys in 2.5 wt% NaCl, 3.5 wt% NaCl solution and Natural Sea Water. Influence of corrosion media on coarse and fine-grained AZ80/91 Mg alloys was discussed in the results and discussion section. Corrosion attack of AZ80/91 Mg alloys under the above environment, increased with increase in chloride ion concentration and decreased with the ECAP passes. © 2021 Elsevier Ltd. All rights reserved.Item Effect of Power Input on Metallurgical and Mechanical Characteristics of Inconel-625 Welded Joints Processed Through Microwave Hybrid Heating(Springer, 2019) Badiger, R.I.; Narendranath, S.; Srinath, M.S.; Hebbale, A.M.In the present study, welding of Inconel-625 through the use of microwave hybrid heating (MHH) has been achieved at two power levels 600 W and 900 W in a low-cost home microwave oven. Nickel-based powder EWAC was used as filler interface between faying surfaces. Effect of power variation on the metallurgical and mechanical characteristics of the microwave welded joints has been investigated. Developed joints were characterized through XRD, optical microscope, SEM, universal testing machine and Vickers microhardness tester. XRD study of the weld zone indicated the formation of various carbides and intermetallics. Joint microstructures witnessed a completely fused weld interface without any interfacial cracks. EDS analysis of the joint microstructure revealed lesser amount of segregation of niobium and molybdenum with the specimens developed at 600 W which could be attributed to the lower heat input associated with 600 W power that also resulted in fine grain structure. Further, the specimens processed at 600 W exhibited better tensile and flexural properties when compared to their counterparts produced at 900 W power. Fractography study of the specimens revealed a combined ductile and brittle fracture. © 2019, The Indian Institute of Metals - IIM.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 Studies on high temperature erosion behavior of HVOF-sprayed (Cr?C?-NiCr)Si and WC-Co/NiCrAlY composite coatings(Elsevier Ltd, 2025) Medabalimi, S.; Hebbale, A.M.; Gudala, S.; Rokkala, U.; Ramesh, M.R.The present study investigates the high temperature erosion behavior of HVOF sprayed composite coatings on T11 steel substrates by studying (Cr?C?-NiCr)Si and WC-Co/NiCrAlY coatings. Phase composition, cross sectional microstructure, mechanical properties, and erosion resistance were analyzed by XRD, EDS, SEM and three-dimensional optical profilography. The results demonstrate that the WC-Co/NiCrAlY coating has higher erosion resistance and oxidation stability for all temperatures and impact angles tested. Its enhanced performance in high temperature and erosive conditions is attributable to the formation of stable protective oxides such as Al?O? and Cr?O? and intermetallic phases such as Ni?Al and Cr?C?. The NiCrAlY matrix prevents significant decarburization of WC particles, and hence phase stability and oxidation resistance. The (Cr?C?-NiCr)Si coating has higher microhardness due to silicide phases, but is more vulnerable to direct impacts and inferior oxidation resistance. The phase transformations for both coatings are favorable at elevated temperatures which enhances erosion resistance. The WC-Co/NiCrAlY coating is smooth and shallower in erosion craters and is perfectly suited for harsh environments demanding high toughness, impact resistance and oxidation stability. For applications in which high hardness is needed in less severe conditions, the (Cr?C?-NiCr)Si coating is more suitable. © 2024Item A microstructural study and high-temperature oxidation behaviour of plasma sprayed NiCrAlY based composite coatings(Elsevier B.V., 2025) Hebbale, A.M.; Ramesh, M.R.; Petr?, J.; Chandramouli, T.V.; Srinath, M.S.; Shetty, R.K.In this study, the development and performance evaluation of plasma sprayed NiCrAlY based coatings, such as NiCrAlY, NiCrAlY + Al?O? and NiCrAlY + YSZ on T91 steel substrates for high temperature applications is carried out. Microstructural features, phase composition and oxidation resistance under cyclic oxidation at 800 °C of the coatings were characterized. Analysis of the XRD confirmed the formation of protective phases such as Cr?O?, Ni?Al and NiAl, and the improvement observed in the coating's performance was due to the addition of Al?O? and YSZ. Oxidation resistance was improved for the NiCrAlY + Al?O? coating through the formation of a dense Al?O? oxide layer, but the NiCrAlY + YSZ coating was superior in terms of thermal stability and spallation resistance, because YSZ has low thermal conductivity and high thermal shock resistance. Composite coatings showed improved cyclic oxidation behavior and microstructural analysis revealed reduced porosity and enhanced integrity. The results demonstrate that the addition of Al?O? and YSZ in the NiCrAlY coatings leads to capability of tailoring NiCrAlY–based coatings for high temperature industrial applications with improved durability and oxidation protection. © 2025 The Author(s)Item Microstructure and elevated temperature wear behavior of HVOF-sprayed SS304L stainless-steel coating(Springer Nature, 2025) Medabalimi, S.; Gudala, S.; Rokkala, U.; Hebbale, A.M.; Ramesh, M.R.The paper aims to investigate the performance of the SS304L stainless steel coating on wear properties by varying load, temperature and velocity. Stainless-steel coatings were fabricated by high-velocity oxy-fuel spraying (HVOF) on superfer800. Surface morphology, elemental distribution and phase analysis were expressed by SEM, EDS, and XRD, respectively. The porosity, average surface roughness, and average microhardness of HVOF stainless steel coating are 2%, 7 µm, and 1167 ± 54 HV0.3, respectively. The wear rate of stainless-steel coating is 0.5 × 10?3 mm3/m at 600 °C with 20 N loads, which is about 16 times lower than the substrate. Adhesion and abrasion are the main wear mechanisms of HVOF stainless steel coatings during high-temperature tests. Comparing to superfer800 substrate, stainless steel coatings showed superior wear resistance at all the loads, temperature and velocities. © The Author(s) 2025.Item Studies on high-temperature erosion behaviour of HVOF sprayed NiCr based composite coatings(Elsevier B.V., 2025) Medabalimi, S.; Hebbale, A.M.; Gudala, S.; Ramesh, M.R.; Gujar, R.; Aravindan, N.; Petr?, J.Solid particle erosion at high temperature is a major problem in many industries and advanced protective coatings are needed to extend the service life of components subjected to harsh environment. The main objective of this study is to investigate the erosion behavior of HVOF sprayed (NiCr) + 5 % Si and (NiCr)+ 2% C based composite coatings at different impact angles and temperature, with specific emphasis on the effect of coating composition. The coatings exhibited excellent erosive wear resistance at elevated temperatures due to the formation of stable oxide layers (CrO, NiCr?O?, SiO?) and the incorporation of silicide phases (Ni?Si) to the NiCrSi coatings. However, NiCrC coatings containing hard carbide phases (such as NiC) showed higher erosion resistance at higher temperatures and normal impact angles (90°) because of their robust microstructure and thermal stability. The analysis of microhardness indicated that NiCrSi coatings provided higher hardness attributable to silicides and were therefore better suited to moderate erosive environments, whereas NiCrC coatings, with slightly lower hardness, exhibited excellent resilience under severe erosive environments. SEM, EDAX and XRD analyses showed that preferential erosion mechanisms were cutting and plowing at oblique angles (30°) and brittle fracture at normal angles (90°). Notably, at 800 °C, NiCrC coatings outperformed the NiCrSi coatings via consistently superior thermal and erosion resistance. These findings indicate that HVOF sprayed NiCrC coatings are suitable for high temperature erosion protection, and NiCrSi coatings are specifically developed for high erosive wear resistance at low impact angles. © 2025 The Author(s)