Faculty Publications
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Item An investigation on high temperature erosion behaviour of plasma sprayed CoCrALY/Al2O3/YSZ on fe and ni based alloys(Universiti Putra Malaysia Press Tower 2, UPM-MDTC Technology Centre Serdang, Selangor 43400, 2017) Nithin, H.S.; Desai, V.; Ramesh, M.R.Parts of aircraft and gas turbines used for power production are subjected to severe erosion damage since aircrafts frequently operate in sandy environment. Low cost fuel such as poor quality coal is used in gas turbines which produce suspended hard particle in the exhaust. In the past, researchers have worked on minimising the erosion by using certain coatings. Development of new coatings is necessary in order to explore further in improving resistance against erosion process under high operating temperature of gas turbine, aero engines and other components. In the present work, the investigation of elevated temperature erosion behaviour of CoCrAlY/Al2O3/YSZ coatings synthesised by plasma spraying on two different base metals, namely, Hastelloy X (Superni 76) and AISI 321 (MDN 321) was carried out. The coated samples were subjected to erosion test at 600ºC with the impact angles of 30º and 90º under steady state condition. Alumina powder was used as erodent material of uneven angular shape of 50 ?m particle size. The morphology and phase formed on eroded surface are characterised using SEM and X-ray diffraction to determine the erosion mechanism. The rate of erosion is determined by weight loss method and the CoCrAlY/Al2O3/YSZ coating showed up to about 25% lower erosion rate than the substrate alloy. It was observed that the erosion resistance of CoCrAlY/Al2O3/YSZ coating on both MDN 321 and Superni 76 gave almost similar erosion resistance which shows that the erosion behaviour of coating is not influenced by substrate unless spray parameter and substrate roughness is changed. © 2017 Universiti Putra Malaysia Press.Item Elevated Temperature Solid Particle Erosion Performance of Plasma-Sprayed Co-based Composite Coatings with Additions of Al2O3 and CeO2(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Nithin, H.S.; Desai, V.; Ramesh, M.R.In this paper, investigation into solid particle erosion behavior of atmospheric plasma-sprayed composite coating of CoCrAlY reinforced with Al2O3 and CeO2 oxides on Superni 76 at elevated temperature of 600 °C is presented. Alumina particles are used as erodent at two impact angles of 30° and 90°. The microstructure, porosity, hardness, toughness and adhesion properties of the as-sprayed coatings are studied. The effects of temperature and phase transformation in the coatings during erosion process are analyzed using XRD and EDS techniques. Optical profilometer is used for accurate elucidation of erosion volume loss. CoCrAlY/CeO2 coating showed better erosion resistance with a volume loss of about 50% of what was observed in case of CoCrAlY/Al2O3/YSZ coating. Lower erosion loss is observed at 90° as compared to 30° impact angle. The erosion mechanism evaluated using SEM micrograph revealed that the coatings experienced ductile fracture exhibiting severe deformation with unusual oxide cracks. Reinforced metal oxides provide shielding effect for erodent impact, enabling better erosion resistance. The oxidation of the coating due to high-temperature exposure reforms erosion process into oxidation-modified erosion process. © 2017, ASM International.Item Elevated temperature solid particle erosion behaviour of carbide reinforced CoCrAlY composite coatings(Institute of Physics Publishing helen.craven@iop.org, 2018) Nithin, H.S.; Desai, V.; Ramesh, M.R.CoCrAlY+WC-Co and CoCrAlY+Cr3C2-NiCr coatings are deposited on nickel based alloy using atmospheric plasma spray technique. Mechanical properties such as microhardness, adhesion strength and fracture toughness of coatings are evaluated. Elevated temperature solid particle erosion behaviour of these coatings are investigated at 600 °C using alumina erodent at 30 and 90° impact angle. Coatings are characterized utilizing Scanning electron microscope (SEM), x-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). CoCrAlY+WC-Co coating shows higher hardness, adhesion strength and fracture toughness than CoCrAlY+Cr3C2-NiCr coating. CoCrAlY+WC-Co coating exhibited approximately 3 times higher erosion resistance than CoCrAlY+Cr3C2-NiCr coating at 90° and 30° impact angles. SEM images of eroded surfaces of coatings reveals the combination of ductile and brittle fracture. CoCrAlY+Cr3C2-NiCr coating shows severe cracks, craters, carbide pull out and chipping than CoCrAlY+WC-Co coating. High temperature erosion is a combination of simultaneous building up of material by oxidation and removal of material by erosion process. Thus reforming the erosion process to oxidation modified erosion process. © 2018 IOP Publishing Ltd.Item Cyclic Oxidation and Hot Corrosion Behavior of Plasma-Sprayed CoCrAlY + WC-Co Coating on Turbine Alloys(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Nithin, H.S.; Vijay, D.; Ramesh, M.R.Components in energy-producing systems suffer a variety of degradation processes such as oxidation and molten salt-induced corrosion as a consequence of complex multi-component gaseous environment. Coatings provide a composition that will grow the protective scale at high temperatures having long-term stability. Plasma spraying was used to deposit CoCrAlY + WC-Co composite coatings on turbine alloys of Hastelloy X and AISI 321. The thermocyclic oxidation behavior of coated alloys was investigated in static air and in molten salt (Na2SO4-60%V2O5) environment at 700 °C. The thermogravimetric technique was used to approximate the kinetics of oxidation in 50 cycles, each cycle consisting of heating and cooling. X-ray diffraction and SEM/EDAX techniques are used to characterize the oxide scale formed. Coated alloys showed a lower corrosion rate as compared to uncoated alloys. The coatings subjected to oxidation and hot corrosion showed slow scale growth kinetics. Preferential oxidation of Co, Cr, W and its spinel blocks the transport of oxygen and corrosive species into the coating by providing a barrier, thereby making the oxidation rate to reach steady state. As compared to the substrate alloys, coatings show better hot corrosion resistance. © 2018, ASM International.Item Hot Corrosion Behaviour of Refractory and Rare Earth Oxide Reinforced CoCrAlY APS Coatings at 700 °C(Springer, 2018) Nithin, H.S.; Desai, V.; Ramesh, M.R.This paper investigates cyclic hot corrosion of plasma sprayed CoCrAlY + Al2O3 + YSZ (C1) and CoCrAlY + CeO2 (C2) composite coatings on MDN 321 and Superni 76 substrates in molten salt (Na2SO4-60%V2O5) environment exposed to 700 °C. Weight change technique is used to evaluate the corrosion performance. Both C1 and C2 coatings showed better corrosion resistance than uncoated alloy. Both the coatings showed linear weight gain during the initial cycles and parabolic weight gain nature with subsequent hot corrosion cycles. The parabolic rate constant (Kp) of C1 and C2 coating was observed to be in the range 0.29–0.32 × 10?10 g2 cm?4 s?1 and 1.0–1.13 × 10?10 g2 cm?4 s?1 respectively. In C1 coating, the globular and continuously packed structure on the corroded surface having CoO, Cr2O3, CoCr2O4 and CoAl2O4 spinel oxides provided superior hot corrosion resistance. While in case of C2 coating, the outward growth of CeVO4 irregular crystals as a corrosion product of CeO2 and V2O5 salt deteriorated the oxide scales resulting in higher corrosion rate. © 2018, The Indian Institute of Metals - IIM.Item EFFECT of LASER POST-TREATMENT on MICROSTRUCTURAL and SLIDING WEAR BEHAVIOR of HVOF-SPRAYED NiCrC and NiCrSi COATINGS(World Scientific, 2022) Naik, T.; Mathapati, M.; Prasad, C.D.; Nithin, H.S.; Ramesh, M.R.In this study, NiCrC and NiCrSi coatings are deposited on the MDN 310 steel using High-Velocity Oxy-Fuel (HVOF) process. Laser Surface Melting (LSM) post-heat treatment is carried out on as-sprayed coatings using Laser Engineered Net Shaping (LENSTM) with a power of 300W. The characteristics of both coatings in terms of mechanical and metallurgical properties have been investigated. The thicknesses of the as-sprayed NiCrC and NiCrSi coatings are in the range of 170-200μm. Laser-treated NiCrC and NiCrSi coatings exhibit a thickness range of 162-185μm, respectively. The microstructure of laser-treated NiCrC-300W coating clearly shows a dendrite-like structure, whereas the laser-treated NiCrSi coating exhibits hard layer and columnar homogeneity. Microhardness of as-sprayed NiCrC coating is 515±15 HV0.3 and that of NiCrSi coating is 645±25 HV0.3. Microhardness of laser-treated NiCrC coating is 720±30 HV0.3 and that of NiCrSi coating is 890±15 HV0.3. Dry sliding wear tests are conducted at room temperature (RT) and 400°C with 10-N and 20-N loads. The wear rates at 400°C temperature of laser-treated NiCrC and NiCrSi coatings produced are slightly below (1-2.2)×10-3mm3/m and (0.8-1.6)×10-3mm3/m, respectively. Laser-treated coatings produced better dry sliding wear behavior compared with as-sprayed coatings owing to dense microstructure. Formation of SiC phase in NiCrSi coating imparts high wear and frictional resistance compared to the NiCrC coating. © 2022 World Scientific Publishing Company.