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Miami, FL, United States

Keshri A.K.,Plasma Forming Laboratory | Singh V.,University of Central Florida | Huang J.,Florida International University | Seal S.,University of Central Florida | And 2 more authors.
Surface and Coatings Technology | Year: 2010

Tribological behavior of plasma sprayed carbon nanotube (CNT) reinforced aluminum oxide (Al2O3) composite coatings was examined at room temperature, 573 K and 873 K using tungsten carbide (WC) ball-on-disk tribometer. The weight loss due to wear of Al2O3 coating was found to be increasing with the temperature while Al2O3-CNT coating showed a decreasing trend in the weight loss with the temperature. Relative improvement in the wear resistance of Al2O3-CNT coating compared to Al2O3 coating was found to be 12% at room temperature which gradually increased to ∼ 56% at 573 K and ∼ 82% at 873 K. Protective layer as a result of tribo-chemical reaction was observed on the wear track of both of the coatings. The improvement in the wear resistance of Al2O3-CNT coating was attributed to three phenomena viz. (i) higher hardness at the elevated temperature as compared to Al2O3 coating, (ii) larger area coverage by protective film on the wear surface at the elevated temperature and (iii) CNT bridging between splats. The coefficient of friction (COF) of Al2O3 coating was nearly constant at room and elevated temperature whereas COF for Al2O3-CNT coating decreased at the elevated temperature (873 K). © 2009 Elsevier B.V. All rights reserved. Source


Lahiri D.,Plasma Forming Laboratory | Dua R.,Florida International University | Zhang C.,Plasma Forming Laboratory | De Socarraz-Novoa I.,Plasma Forming Laboratory | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2012

Graphene nanoplatelets (GNPs) are added as reinforcement to ultrahigh molecular weight polyethylene (UHMWPE) with an intended application for orthopedic implants. Electrostatic spraying is established as a potential fabrication method for synthesizing large-scale UHMWPE-GNP composite films. At a low concentration of 0.1 wt % GNP, the composite film shows highest improvement in fracture toughness (54%) and tensile strength (71%) as compared to UHMWPE. Increased GNP content of 1 wt % leads to improvement in elastic modulus and yield strength but fracture toughness and tensile strength are reduced significantly at higher GNP content. The strengthening mechanisms of the UHMWPE-GNP system are highly influenced by the GNP concentration, which dictates its degree of dispersion and extent of polymer wrapping. The fraction of GNPs oriented along the tensile axis influences the elastic deformation, whereas the wrapping of polymer and GNP-polymer interfacial strength determines the deformation behavior in the plastic regime. The cytotoxicity of GNP to osteoblast is dependent on its concentration and is also influenced by agglomeration of particles. Lowering the concentration of GNPs in UHMWPE improves the biocompatibility of the composite surface to bone cells. The survivability of osteoblasts deteriorates up to 86% on 1 wt % GNP containing surface, whereas much smaller (6-16%) reduction is observed for 0.1 wt % GNP over 5 days of incubation. © 2012 American Chemical Society. Source


Bakshi S.R.,Plasma Forming Laboratory | Lahiri D.,Plasma Forming Laboratory | Patel R.R.,Plasma Forming Laboratory | Agarwal A.,Plasma Forming Laboratory
Thin Solid Films | Year: 2010

Nanoscratch experiments have been carried out on plasma sprayed aluminum alloy coatings reinforced with 0, 5 and 10 wt.% carbon nanotubes (CNTs). Scratches have been performed at loads of 1000, 2000 and 3000 μN load using Berkovich indenter. The contact and true wear volumes of the scratches have been calculated. The nano-scale wear resistance is shown to increase by 4 times by addition of 10 wt.% CNTs. Improvement in the wear resistance is discussed with respect to strengthening effect and increased elastic recovery by addition of CNTs. Direct evidence of increased recovery and small decrease in the coefficient of friction with CNT content is provided using the true and instantaneous depth plots and the corresponding scanning probe microscope and scanning electron microscope images of the scratches. Friction coefficient was found to be load independent and was found to vary slightly with the CNT content. © 2009 Elsevier B.V. All rights reserved. Source

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