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Brostow W.,Center for Advanced Research and Technology | Czechowski K.,Institute of Advanced Manufacturing Technology | Polowski W.,Institute of Advanced Manufacturing Technology | Rusek P.,Institute of Advanced Manufacturing Technology | And 2 more authors.
Materials Research Innovations | Year: 2013

We have performed surface modification of selected tool steels. The steels were covered with adhesive coatings of the hard chrome type or with diffusion layers of the nitride type. We have investigated in particular surface roughness, since it is known to affect friction, lubrication and wear. We have also considered an accumulation of strain energy in the strained area, which accompanies the crystal lattice deformation caused by burnishing. Surface roughness was determined by a profilometer before and after burnishing. Adhesion of coatings to steel was determined with a scratch tester. A combination of both approaches, slide burnishing with hard chrome coating and/or slide burnishing with nitriding, seems worthwhile. Both treatments and their combinations can be used in manufacturing tools and structural elements in automotive and aerospace industries. © W. S. Maney & Son Ltd. 2013.

Orozco V.H.,Center for Advanced Research and Technology | Orozco V.H.,University of Antioquia | Vargas A.F.,Center for Advanced Research and Technology | Vargas A.F.,University of Antioquia | And 6 more authors.
Journal of Nanoscience and Nanotechnology | Year: 2014

Carbon nanotubes (CNTs) and sepiolite (SEP) were modified in order to improve their compatibility with the polypropylene (PP) matrix. Carboxylic groups were introduced into the CNTs through an oxidative treatment and aliphatic chains were incorporated on SEP by ion exchange of a cationic surfactant. Maleic anhydride grafted polypropylene (PPgMA) was mixed with neat PP to introduce polar groups into the polymer matrix. Composites including modified and non-modified fillers were prepared by melt extrusion. Dispersion and interaction of the CNTs with the PP and PPgMA matrices were evaluated by Raman spectroscopy while a focused ion beam/scanning electron microscopy (FIB/SEM) was used for SEP containing composites. Scratch resistance, microhardness, dynamic friction and wear were determined. Raman spectroscopy shows that the introduction of polar groups into PP matrices has a positive effect on the dispersion of modified CNTs. FIB/SEM results show that the modification of SEP improves its dispersion in the polypropylene matrix; filler clusters found in the PPgMA matrix are much times smaller than those in the neat PP. Despite of SEP agglomerates in the composites, a good interaction between both phases is seen; SEP particles are fully coated and embedded inside the PP matrix. The 'lack of cooperation' between unmodified PP and its fillers results in nanocomposites with larger residual depths; by contrast, PPgMA does 'cooperate' with its fillers so that the nanocomposites in scratch resistance testing have smaller residual depths Rh than the neat PPgMA. Addition of the fillers to PPgMA also increases the hardness. As for wear rates, some our fillers provide higher and some lower wear rates than PP. Copyright © 2014 American Scientific Publishers All rights reserved.

Dahotre S.N.,Texas Academy of Mathematics and Science TAMS | Vora H.D.,Center for Advanced Research and Technology | Vora H.D.,University of North Texas | Rajamure R.S.,Center for Advanced Research and Technology | And 7 more authors.
Annals of Biomedical Engineering | Year: 2014

The osseo-integration, corrosion resistance, and tribological properties of the commonly used bioimplant alloy Ti-6Al-4V were enhanced using a laser-based surface nitridation process. The biomedical properties of the laser nitrided Ti-6Al-4V were investigated using experimental and computational methodologies. Electrochemical analysis of laser nitrided titanium in simulated body fluid (SBF) was performed to assess the biomedical characteristics in near-human body conditions. Additionally, the corrosive wear performance of these laser nitrided samples was evaluated using pin-on-disk geometry with a zirconia pin counter surface in SBF to mimic the biological scenario. Osteoblast studies were conducted to evaluate cell affinity towards titanium nitrided bioimplant material. Cells adhered to all substrates, with high viability. Initial cell adhesion was revealed by focal adhesion formation on all substrates. Cells can proliferate on samples treated with 1.89 and 2.12 × 106 J/m2 laser conditions, while those treated with 1.70 × 106 J/m2 inhibited proliferation. Thus, microstructural and phase observations, electrochemical analyses, corrosive wear evaluation, and cell behavior analysis of laser nitrided surface of bioimplant material (Ti-6Al-4V) indicated that laser nitriding greatly improves the performance of bioimplant material. © 2013 Biomedical Engineering Society.

Dahotre S.N.,Texas Academy of Mathematics and Science TAMS | Dahotre S.N.,University of North Texas | Vora H.D.,Center for Advanced Research and Technology | Vora H.D.,University of North Texas | And 4 more authors.
Applied Surface Science | Year: 2013

Titanium and its alloys have been commonly used in many biological and industrial applications owing to their excellent mechanical and physical properties. However, they have been specifically inadequate for biomedical implants due to their inferior tribological properties (low wear resistance, higher coefficient of friction, and lower hardness). As a remedy, the process of laser nitriding has emerged from the past few decades as a unique method for tailoring the surface microstructures and/or composition of titanium for enhanced tribological characteristics of titanium and its alloys. In the present study, a multiphysics computational model was developed to predict the nitrogen diffusion length into the Ti-6Al-4V alloy under various laser processing conditions (laser power and scanning speed). XRD, SEM and EDS analyses were also conducted for phase identification, microstructural investigation, and estimating the nitrogen concentration, respectively. Both computational and experimental results indicated that the depth of nitrogen diffusion increased with decrease in scanning speed, and subsequent increase in laser interaction time and increase in input laser energy density. © 2013 Elsevier B.V.

Vora H.D.,Center for Advanced Research and Technology | Vora H.D.,University of North Texas | Shanker Rajamure R.,Center for Advanced Research and Technology | Shanker Rajamure R.,University of North Texas | And 8 more authors.
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2014

A laser based surface nitriding process was adopted to further enhance the osseo-integration, corrosion resistance, and tribological properties of the commonly used bioimplant alloy, Ti-6Al-4V. Earlier preliminary osteoblast, electrochemical, and corrosive wear studies of laser nitrided titanium in simulated body fluid clearly revealed improvement of cell adhesion as well as enhancement in corrosion and wear resistance but mostly lacked the in-depth fundamental understanding behind these improvements. Therefore, a novel integrated experimental and theoretical approach were implemented to understand the physical phenomena behind the improvements and establish the property-structure-processing correlation of nitrided surface. The first principle and thermodynamic calculations were employed to understand the thermodynamic, electronic, and elastic properties of TiN for enthalpy of formation, Gibbs free energy, density of states, and elastic properties of TiN were investigated. Additionally, open circuit potential and cyclic potentio-dynamic polarization tests were carried out in simulated body fluid to evaluate the corrosion resistance that in turn linked with the experimentally measured and computationally predicted surface energies of TiN. From these results, it is concluded that the enhancement in the corrosion resistance after laser nitriding is mainly attributed to the presence of covalent bonding via hybridization among Ti (p) and N (d) orbitals. Furthermore, mechanical properties, such as, Poisson's ratio, stiffness, Pugh's ductility criteria, and Vicker's hardness, predicted from first principle calculations were also correlated to the increase in wear resistance of TiN. All the above factors together seem to have contributed to significant improvement in both wear and corrosion performance of nitride surface compared to the bare Ti-6Al-4V in physiological environment indicating its suitability for bioimplant applications. © 2014 Elsevier Ltd.

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