Journal Articles
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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 Factors influencing powders’ flowability and favorable phases like crystalline (Mullite and quartz) and amorphous phases of plasma-sprayed fly ash coatings suitable for marine and offshore applications(Elsevier B.V., 2023) Bhajantri, V.F.; Jambagi, S.C.Due to its rich mineralogy, fly ash (FA), an industrial waste, has been used to combat erosive, corrosive environments. Powder flowability dictates coating properties. In this investigation, raw FA powder was obtained from a thermal power plant and sieved in various sizes to assess their flowability. Powder's physical characteristics, such as specific surface area, Blaine's fineness number, and bulk density, were determined, and their influence on powder flowability was analyzed. Of these properties, bulk density affects more. Rietveld refinement was performed on the powder to quantify the phases. The powders had 45.08 ± 11.38 amorphous and 11.00 ± 2.76 % of mullite phases. Later, alumina was added between 10 and 50 wt% to FA, and samples were subjected to high-temperature X-ray diffraction at 1150 °C. A ∼32.27% rise in Mullite content was observed for 50 wt% alumina, with ∼119% decrease in the amorphous phase. Finally, one set of FA without additives coating was plasma sprayed onto a marine-grade steel substrate. The coating showed ∼17.31 ± 0.6% of mullite and ∼69.43 ± 0.6 % of the amorphous phase, with decent Mechanical properties. Therefore, 50 wt% alumina in FA powder has improved the mullite phase, bulk density (43%), and flowability by decreasing the amorphous phase content. © 2023 Society of Powder Technology JapanItem Thermal spray processes influencing surface chemistry and in-vitro hemocompatibility of hydroxyapatite-based orthopedic implants(Elsevier Ltd, 2024) Shankar, D.; Jayaganesh, K.; Gowda, N.; Lakshmi, K.S.; Jayanthi, K.J.; Jambagi, S.C.Orthopedic implants made from titanium are a popular choice in the medical field because of their remarkable strength-to-weight ratio. Nevertheless, they may not interact well with human blood, resulting in thrombosis and hemolysis. In fact, non-hemocompatibility is believed to be responsible for about 31 % of medical device failures in the US alone, requiring painful and expensive revision surgery. To address this issue, bioactive hydroxyapatite coatings are applied to Ti-6Al-4V implants using thermal spray techniques. However, the temperature used during thermal processing impacts the coating's surface properties, affecting the mechanical and biological properties. Furthermore, the effectiveness of HA coatings on titanium for orthopedic applications has not been validated by biocompatibility tests, particularly hemocompatibility. In this study, we aimed to investigate the relative efficacy of three thermal spray processes of different temperature ranges: Atmospheric plasma spray (APS) (high temperature), Flame spray (FS) (moderate temperature), and High-Velocity Oxy-Fuel spray (HVOF) (low temperature), and study their impact on coating's surface properties, affecting blood components and implant's strength. The crystallinity of the HA coating increased by 32 % with a decrease in the operating temperature (APS < FS < HVOF). HVOF coating exhibited a ~ 34 % and ~ 120 % improvement in adhesion strength and ~ 31 % and 59 % increment in hardness compared to APS and FS coating, respectively, attributed to its low porosity, low coating thickness (~55 μm), and high degree of crystallinity. The HVOF coating showcased a significant increase in non-hemolytic behavior, with hemolysis rates ~8 and ~ 11 times lower than APS and FS coatings, respectively, owing to its smooth texture and high degree of crystallinity (p < 0.05). Furthermore, the HVOF coating exhibited minimal blood clotting based on the whole blood clotting assay, again confirmed by PT and aPTT assays showing delayed clotting time, indicating its non-thrombogenic behavior. The number of platelets adhered to the three coatings showed no significant difference compared to Ti-6Al-4V. APS and FS coatings showed low platelet activation, unlike HVOF coating and titanium, which revealed round platelets, similar to the negative control. Neither titanium nor HA coatings exhibited antibacterial properties, which may be due to their high affinity for organic substances, which promotes bacterial adhesion and replication. Among the three thermal processes, HVOF coating displayed good apatite growth, non-hemolytic, and non-thrombogenicity with no platelet activation owing to its low processing temperature, high degree of crystallinity (89.7 %), hydrophilicity, smooth (~4 μm) and dense (~97 %) microstructural properties. The results demonstrated that the HVOF-HA coating presented in this work meets the hemocompatible requirements and shows promise for prospective application as an orthopedic implant. Furthermore, this study has the potential to significantly reduce the use of animals in in-vivo research and improve their welfare while also cutting costs. © 2024 Elsevier B.V.Item 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 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.