Faculty Publications
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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 Influence of carbon nanotube reinforcement on the heat transfer coefficient, microstructure, and mechanical properties of a die cast Al-7Si-0.35Mg alloy(Elsevier Ltd, 2021) Usef, A.P.; Bhajantri, V.; Kannoth, V.; Jambagi, S.C.Al-7Si-0.35Mg or A356 alloy is most widely used in aircraft and automobile industries owing to its high strength to weight ratio. This alloy has been reinforced with a 1 wt% carbon nanotube (CNT) to improve its properties in this investigation. First, A356/1 wt% CNT powders were ball milled in the presence of ethanol and subsequently consolidated using gravity die casting. Ball milling was effective in achieving homogeneous dispersion of CNT. The microstructural study revealed the segregation of the Al4C3 phase at the grain boundary. This mechanism is known as grain boundary precipitation. Also, the grain size has decreased by ~44%. Next, the casting-die interfacial heat transfer coefficient (IHTC) has been evaluated using Beck's inverse heat transfer algorithm. With the reinforcement, the IHTC has increased by ~2.5%, which indicates the rise in heat transfer rate during solidification. Then, the experimental and theoretical tensile properties of A356 were correlated using simulation software. The experimental results showed the synergistic effect of grain size, Al4C3, and IHTC improving yield strength by ~19.8%, ultimate tensile strength by ~14.13%, elongation by 7%, and hardness ~22%. Therefore, a meagre 1 wt% CNT has improved the heat transfer rate of the melt as indicated by IHTC values. This effect was further corroborated by evaluating the thermal conductivity of the sample. The thermal conductivity has improved by 10% that resulted in finer grain size of the sample. Therefore, such reinforced alloys are expected to display higher strength demanded in various industrial applications. © 2021Item An investigation of slurry erosion behaviour in plasma-sprayed carbon nanotube-reinforced fly ash/alumina coatings using experimental analysis and artificial neural computing for marine and offshore applications(Elsevier Ltd, 2024) Chavana, N.; Anil, A.; Jambagi, S.C.This study investigates carbon nanotube (CNT)-reinforced alumina fly ash (FA) coatings, namely AF (unreinforced), 1CAF (with 1 wt% CNT), and 2CAF (with 2 wt% CNT), on marine-grade steel. Microstructural analysis shows 1CAF coatings denser by ∼15.32% due to CNT reinforcement, while 2CAF coatings display ∼9.68% increased porosity from CNT agglomeration. Raman spectroscopy confirms CNT retention. 1CAF coatings exhibit ∼14.66% higher microhardness, ∼15.96% higher adhesion strength, and ∼15.66% improved fracture toughness compared to AF coatings, attributed to pore sealing through CNT reinforcement. Enhanced erosion resistance (∼14.59%) in 1CAF coatings was observed due to improved mechanical properties and CNTs mitigating crack propagation. Validation through an artificial neural network (ANN) modeling and regression analysis supports 1CAF coatings’ promise for harsh marine environments, offering enhanced durability. © 2024 Elsevier LtdItem Improvements in bioactivity, blood compatibility, and wear resistance of thermally sprayed carbon nanotube reinforced hydroxyapatite-based orthopedic implants(Elsevier Ltd, 2024) Shankar, D.; Jambagi, S.C.Titanium implants often fail due to aseptic loosening and non-hemocompatibility, necessitating costly revision surgeries. This study investigated the wear performance and biocompatibility of high-velocity oxy-fuel (HVOF) sprayed-hydroxyapatite (HA) and HA/alumina-19 wt%/carbon nanotube (CNT)− 1 wt% (HAC1) coatings. The novel heterocoagulation colloidal technique effectively dispersed CNTs, enhancing adhesion strength by ∼120 %, hardness by ∼45 %, and wear resistance by ∼32 % in simulated body fluid (SBF) and 17 % in dry conditions versus HA coatings, attributed to the low coefficient of friction (CoF) (1.16–1.48 times than HA) due to lubrication offered by peeled-off graphite layers from the CNT surface. Additionally, HAC1 implants exhibited superior apatite growth (∼52 % than HA), excellent non-hemolytic behavior (∼0.2 %), and no platelet activation, making it highly promising for orthopedic applications. © 2024 Elsevier LtdItem An effective utilization of raw fly ash obtained from thermal power plants using thermal spray technique to improve corrosion resistance for marine applications(Elsevier Ltd, 2024) Chavana, N.; Jambagi, S.C.Marine-grade steel structures in offshore environments often corrode due to the aggressive environmental conditions. Many ceramic materials can cater to this demand. However, as per economic and ecological concerns, fly ash (FA), an industrial waste, can be another strong contender to control corrosion. Therefore, the present study developed composite coatings of fly ash with additives ((50-48) wt.% Al2O3; 0–2 wt% carbon nanotube (CNT)) onto marine-grade steel using a plasma spray technique to improve its corrosion resistance. The microstructure of 1 wt% CNT-reinforced alumina-FA (1CAF) coating was denser than 2 wt% CNT-reinforced alumina-FA (2CAF) coating due to the uniform dispersion of CNT and, thereby, uniform remelting of coating at localized sites. Consequently, the microhardness and adhesion strength of the 1CAF coating were improved by ∼14.66 % and ∼15.96 %, respectively. Further, Rietveld's analysis of coatings showed that quartz, being the primary phase for corrosion control, was 19.23 ± 0.87 %, 16.33 ± 1.04 % and 14.60 ± 1.87 % for alumina-FA (AF), 1CAF, and 2CAF, respectively. The electrochemical impedance spectroscopy and the salt spray corrosion tests showed that 1CAF coating corrosion resistance was improved by ∼11.2 % compared to AF coating, even with a lower quartz phase (∼15.08 %) due to the densification of coating. This densification was due to the remelting by CNT to seal pores in the coating. Furthermore, for the same reason, an increase in coating resistance and charge transfer resistance of 1CAF coating by ∼80.9 % and ∼19.93 %, respectively, were seen in the equivalent circuit analysis, showing great promise in controlling interfacial corrosion. Further post-treatments like plasma or laser treatments can seal the coatings further to improve corrosion resistance. Therefore, such coatings are expected to withstand harsh, corrosive environments and are well-suited for marine applications. © 2024 Elsevier B.V.Item Numerical and Experimental Investigation of Thermal Barrier Effects of CNT-Reinforced Fly Ash/Alumina Coatings in Diesel Engine Pistons(American Chemical Society, 2025) Chavana, N.; Sarkar, B.; Jambagi, S.C.Fly ash (FA), an industrial byproduct from coal combustion, presents significant disposal challenges, especially in developing nations. Given its mineralogical properties, FA shows potential in thermal spray coatings. This study evaluates FA-based coatings for pistons to improve thermal management in internal combustion engines through numerical simulations, analyzing their effects on the temperature distribution, thermal stress, and combustion efficiency. FA coatings were also applied to marine-grade steel with additives (50 wt % Al2O3 and 0-2 wt % CNT) to assess high-temperature performance. Microstructural analysis revealed that 2 wt % CNT-reinforced (2CAF) coatings showed agglomeration, reducing microhardness by ?9.27% compared to 1 wt % CNT-reinforced (1CAF) coatings. The XRD analysis of 1CAF indicated ?56.51% transformation of corundum to ?-alumina, lowering thermal conductivity by ?15.40% compared to alumina/FA (AF) coatings, while 2CAF coatings showed increased conductivity due to CNT inhomogeneity. For piston applications, simulations showed an ?24.59% rise in maximum surface temperature, from 241.39 to 300.76 °C, and an ?62.06% reduction in heat flux, indicating enhanced durability and reduced cold-start emissions. Thermal cycling demonstrated that 1CAF coatings outlasted AF and 2CAF, suggesting FA-based TBCs as sustainable and economical options for enhanced engine performance and waste valorization. © 2025 American Chemical Society.