Faculty Publications
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Item Role of zirconia filler on friction and dry sliding wear behaviour of bismaleimide nanocomposites(2011) Kurahatti, R.V.; Surendranathan, A.O.; Srivastava, S.; Singh, N.; Ramesh Kumar, A.V.; Suresha, B.This paper discusses the friction and dry sliding wear behaviour of nano-zirconia (nano-ZrO2) filled bismleimide (BMI) composites. Nano-ZrO2 filled BMI composites, containing 0.5, 1, 5 and 10wt.% were prepared using high shear mixer. The influence of these particles on the microhardness, friction and dry sliding wear behaviour were measured with microhardness tester and pin-on-disc wear apparatus. The experimental results indicated that the frictional coefficient and specific wear rate of BMI can be reduced at rather low concentration of nano-ZrO2. The lowest specific wear rate of 4×10-6mm3/Nm was observed for 5wt.% nano-ZrO2 filled composite which is decreased by 78% as compared to the neat BMI. The incorporation of nano-ZrO2 particles leads to an increased hardness of BMI and wear performance of the composites shows good correlation with the hardness up to 5wt.% of filler loading. The results have been supplemented with scanning electron micrographs to help understand the possible wear mechanisms. © 2011 Elsevier Ltd.Item Combating corrosion degradation of turbine materials using HVOF sprayed 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY coating(2013) Jegadeeswaran, N.; Ramesh, M.R.; Bhat, K.High velocity oxy fuel process (HVOF) is an advanced coating process for thermal spraying of coatings on to components used in turbines. HVOF process is a thermal spray coating method and is widely used to apply wear, erosion, and corrosion protective coatings to the components used in industrial turbines. 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY based coatings have been sprayed on to three turbine materials, namely, Ti-31, Superco-605, and MDN-121. Coated and uncoated substrates were subjected to hot corrosion study under cyclic conditions. Each cycle consisted of 1 hour heating at 800°C followed by 20 minutes air cooling. Gravimetric measurements were done after each cycle and a plot of weight gain as a function of number of cycles is drawn. Parabolic rate constants were estimated for the understanding of corrosion behaviour. It was observed that coated Ti-31 and MDN-121 were more resistant compared to the uncoated ones. Uncoated superco-605 was undergoing sputtering during corrosion study and hence comparison between coated and uncoated superco-605 was difficult. The cross-sectional analysis of the corroded, coated samples indicated the presence of a thin layer of chromium oxide scale on the top of the coating and it imparted better corrosion resistance. Parabolic rate constants also indicated that coating is more beneficial to Ti-31 than to MDN-121. © 2013 N. Jegadeeswaran et al.Item High temperature corrosion behaviour of HVOF sprayed WC-CrC-Ni coatings(Inderscience Publishers, 2016) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.; RAMESH, C.S.The present work aims to study the hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-CrC-Ni coating developed on three types of boiler tube materials such as SA213-T22, MDN-310 and Superfer 800 H steels. Hot corrosion studies were conducted in a molten salt environment of Na2SO4-60%V2O5 at 700°C and thermogravimetric analysis was used to establish kinetics of corrosion. Corrosion kinetics of coated steels followed nearly parabolic behaviour and showed a lower corrosion rate in comparison to uncoated alloys. It is concluded that corrosion is restricted to the external surface of the coating and the formation of thick scale composed of oxides of Cr, Ni and their spinel oxides, acts as a diffusion barrier to the transportation of corrosive species into the coating. The carbides of tungsten and chromium uphold the strength of the coating. © © 2016 Inderscience Enterprises Ltd.Item Scratch adhesion strength of plasma sprayed carbon nanotube reinforced ceramic coatings(Elsevier Ltd, 2017) Jambagi, S.C.This report investigates the effect of both mechanical and thermal properties of Carbon nanotube (CNT) on scratch adhesion strength of ceramic coatings. Micro sized alumina and titania with 1 wt% CNT powders were prepared by three routes: dry/wet milling (with alcohol) and heterocoagulation. First, degree of CNT dispersion in the coatings was analysed. Heterocoagulated coatings displayed homogeneous dispersion of CNT. Next, the effect of homogeneous dispersion on phase transformation was studied. Higher thermal conductivity of CNT and its degree of dispersion seemed to affect the melting of powders and thus the phase transformations in the coatings. A higher fraction of stable phase was detected in the coatings. In addition, CNT/ceramic interface was analysed for the reaction layer. A stable phase layer was found covering the entire CNT surface, protecting it from thermal degradation. Finally, the scratch adhesion strength was quantified for both CNT reinforced and unreinforced coatings. The scratch resistance of heterocoagulated coatings improved by ?36–176%. Improvement in strength was attributed to: a) a higher stable phase fraction in the coatings, b) Strong wettability at CNT/ceramic interface, c) improvement in elastic moduli of the coatings has also led to the improvement in the work of adhesion of the coatings, and d) a toughening mechanism, CNT bridging. © 2017 Elsevier B.V.Item Role of thermally grown oxide and oxidation resistance of samarium strontium aluminate based air plasma sprayed ceramic thermal barrier coatings(Elsevier B.V., 2017) Baskaran, T.; Arya, S.B.Samarium Strontium Aluminate (SSA) based ceramic oxide was synthesized and coated on a bond coated (NiCrAlY) Inconel 718 superalloy by air plasma spray (APS) process. Thermally grown oxide (TGO) thicknesses were controlled at different pre-oxidation times of 10, 20 and 30 h at 1050 °C in the argon atmosphere, the highest TGO thickness being found for 30 h pre-oxidized samples. The percentage elastic recovery of pre-oxidized samples increased (45, 48, and 50%) with an increasing pre-oxidation time at 1050 °C. The isothermal oxidation test was performed on pre-oxidized samples at 1100 °C for 15 h in air. The parabolic oxidation rate constant decreased from 6.08 × 10? 5 to 3.90 × 10? 5 mg2 cm? 4 s? 1 (from 10 to 20 h) and then increased up to 4.55 × 10? 5 mg2 cm? 4 s? 1 for 30 h pre-oxidized SSA samples at 1100 °C. SSA based TBCs showed 65% lower weight gain as compared to conventional YSZ TBCs after oxidation at 1100 °C in air. Cross-sectional SEM results revealed that the threshold TGO thickness of SSA TBCs is about 5.3 to 5.8 ?m. Failure of SSA TBCs was observed at the interface of TGO and ceramic top coat due to the formation of SmAlO3 along with spinel oxides. © 2017Item 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 HVOF sprayed Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings: Microstructure, microhardness and oxidation behaviour(Elsevier Ltd, 2018) Reddy, N.C.; Kumar, B.S.A.; Reddappa, H.N.; Ramesh, M.R.; Koppad, P.G.; Kord, S.This paper reports the development of Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings on AISI 420 stainless steel (MDN-420) and titanium alloy ASTM B265 (Ti-15) by HVOF technique. Microstructure, microhardness and high temperature oxidation behaviour of coatings were investigated. Microstructure of coatings was dense and displayed layers depicting lamellar structure. The microhardness of coatings was significantly higher than that of substrate owing to higher density and cohesive strength between individual splats of coating materials. Cyclic oxidation studies conducted on Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings showed oxide scale was composed of various oxides like NiO, NiCr2O4 and Cr2O3 phases. The formation of compact and protective NiO phase in case of Ni3Ti coatings; NiO and Cr2O3 phases in Ni3Ti+(Cr3C2+20NiCr) coatings stabilised the weight gain exhibited slow oxidation rate at higher temperatures. © 2017 Elsevier B.V.Item Influence of ceramic top coat and thermally grown oxide microstructures of air plasma sprayed Sm2SrAl2O7 thermal barrier coatings on the electrochemical impedance behavior(Elsevier B.V., 2018) Baskaran, T.; Arya, S.B.Electrochemical impedance spectroscopy (EIS) technique is used to examine the top coat and thermally grown oxide (TGO) microstructures of Samarium Strontium Aluminate (SSA) thermal barrier coatings (TBCs) after exposed to pre-oxidation and oxidation at 1050 and 1100 °C, respectively. EIS spectra showed that the three relaxations frequencies in Bode plot corresponded to SSA top coat, TGO, and TGO-bond coat interface. A significant reduction in polarization resistance of SSA top coat and increase in capacitance for different pre-oxidation times of 10, 20 and 30 h are being found due to increasing the defects (pores and cracks) of about 13, 29 and 45%, respectively at 1050 °C. The reduction in bi-axial residual stresses was calculated to be about 57% as a consequence of decrement in top coat resistance. The growth of SSA TGO was found from 10 to 20 h of pre-oxidation treatment caused to decrease the capacitance which indicates the presence of highly enriched ?-Al2O3 at the bond coat-top coat interface. The highest charge transfer resistance and lowest capacitance were found to be about 0.48 × 106 ? cm2 and 1.1 nF cm?2 respectively for 20 h of pre-oxidation which could reflect the overall impedance kinetics of TBC system (SSA top coat and TGO) at the TGO-bond coat interface. The impedance responses of SSA top coat, TGO, and TGO-bond coat interface were reduced drastically after oxidation at 1100 °C for 10 h pre-oxidized specimen as compared to 20 and 30 h due to the compositional change of pure ?-Al2O3 based TGO into more conductive NiCr2O4. The lowest diffusion coefficient, DCr3+ in the NiO lattice which reduced the formation of metal ion vacancies at the TGO-top coat interface caused to exhibit higher TGO resistance for 20 h pre-oxidized specimens over 10 and 30 h after oxidation at 1100 °C. © 2018 Elsevier B.V.Item Influence of microwave hybrid heating on the sliding wear behaviour of HVOF sprayed CoMoCrSi coating(Institute of Physics Publishing helen.craven@iop.org, 2018) Prasad, C.D.; Joladarashi, S.; Ramesh, M.R.; Srinath, M.S.; Channabasappa, B.H.CoMoCrSi superalloy powder (Tribaloy-T400) consists of intermetallic laves phase and primary eutectic phase of Co-rich solid solution. Processing of Tribaloy-T400 powder is carried out through high-energy ball milling (HEBM) technique to obtain a higher volume fraction of intermetallic laves phases. The feedstock is sprayed using high-velocity-oxy-fuel (HVOF) process on titanium grade-15 substrate. The coating microstructure is homogenized by microwave hybrid heating technique. Characterization of feedstock, as-sprayed and microwave fused coatings is done by using Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy (EDS) and x-ray Diffraction (XRD). Porosity, surface roughness, microhardness, and bond strength are measured. Adhesive wear behavior of the coatings under the dry sliding condition is evaluated at an applied load of l0 and 20 N and temperature of 200, 400 and 600 °C Fused coating exhibit higher wear resistance than the as-sprayed coatings and substrate. The hard intermetallic laves phases which are amorphous (bulk metallic glass) in nature strengthen the coating at high temperatures. © 2018 IOP Publishing Ltd.Item Hot corrosion resistance of air plasma sprayed ceramic Sm2SrAl2O7 (SSA) thermal barrier coatings in simulated gas turbine environments(Elsevier Ltd, 2018) Baskaran, T.; Arya, S.Samarium strontium aluminate (Sm2SrAl2O7-SSA) and Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were developed on NiCrAlY bond coated Inconel 718 superalloy substrate using air plasma spray process. The hot corrosion study was conducted in simulated gas turbine environments (molten mixtures of 50 wt% Na2SO4 + 50 wt% V2O5 and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl) for two different temperatures of 700 and 900 °C. A developed SSA TBCs showed about 8% and 22% lower lifetime at 700 and 900 °C, respectively than YSZ TBCs in 50 wt% Na2SO4 + 50 wt% V2O5 (vanadate). The hot corrosion life of SSA TBCs being found about 13% and 39% lower than YSZ TBCs in 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl (chloride) at 700 and 900 °C, respectively. X-ray diffraction results showed the formation of SmVO4, SrV2O6, and SrSO4 as a major hot corrosion product in 50 wt% Na2SO4 + 50 wt% V2O5 and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl environments respectively for SSA TBCs. Similarly, YSZ TBCs also showed YVO4 as hot corrosion product in vanadate and chloride environments. Both the TBCs suffer a more severe hot corrosion attack in chloride environment at 900 °C. The leaching of Sr2+ and Y3+ ions from SSA and YSZ respectively play a vital role in the destabilization of coating in vanadate and chloride environments at 700 and 900 °C. In both SSA and YSZ TBCs, the leaching of ion has significantly low influence as compared to attack by chloride ions at the bond coat-top coat interface in the presence of chloride environment. The hot corrosion resistance of SSA TBCs was improved three times higher in the presence of MgO and NiO inhibitor in vanadate environment at 900 °C mainly due to the formation of a stable Ni3V2O8 phase at the surface. © 2018 Elsevier Ltd and Techna Group S.r.l.