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Chicot D.,Lille Laboratory of Mechanics | N'Jock M.Y.,Lille Laboratory of Mechanics | Roudet F.,Lille Laboratory of Mechanics | Decoopman X.,Lille Laboratory of Mechanics | And 5 more authors.
International Journal of Mechanical Sciences | Year: 2016

In this work, the total and plastic hardness of a variety of materials were determined from the work-of-indentation. We show that by taking into account the influence of the tip defect, both the total and plastic hardness have the same values and that the hardness-load dependence is considerably reduced, thus explaining that part of the indentation size effect can be related to an incorrect estimation of the tip defect. To consider the influence of the indenter tip defect, we propose a calculation of the impression volume involving the length of the truncated indenter tip. For the residual impression volume, we have demonstrated that it can be simply calculated from the total volume using a proportionality constant equal to the residual to maximum depth ratio. Moreover, the hardness derived from work-of-indentation is found to be equal to the Meyer hardness. Finally, the ratios of Meyer hardness to the reduced modulus and elastic work to total work of indentation are found to be very close to the proportionality factor (π tanα) of Stilwell and Tabor. © 2015 Elsevier Ltd. All rights reserved.

Gil L.E.,National University of Costa Rica | Liscano S.,National University of Costa Rica | Goudeau P.,University of Poitiers | Le Bourhis E.,University of Poitiers | And 3 more authors.
Surface Engineering | Year: 2010

The present study has been carried out to evaluate the corrosion performance of three different (Ti1-xAlx)N/TiN multilayers coatings commercially deposited on WC-Co inserts. Two of these coatings were nanostructured, and all of them presented different Ti/Al atomic ratios varying from 2 : 3 up to 7 : 3 and were deposited by employing a commercial physical vapour deposition cathodic arc process. X-ray diffraction analysis indicated that the grain size for both the TiAlN and TiN layers in the coatings architecture, varied between approximately 9 to 14 nm. The corrosion performance was evaluated in a 3 wt-%NaCl solution using both open circuit potential and potentiodynamic polarisation measurements. Scanning electron microscopy and energy dispersive spectroscopy surface characterisation before and after corrosion testing allowed the determination that all the coatings under study show a corrosion current density of approximately one order of magnitude smaller than the uncoated substrate, indicating thus their beneficial effect from the corrosion protection viewpoint. © 2010 Maney Publishing.

Santana Y.Y.,Central University of Venezuela | La Barbera-Sosa J.G.,Central University of Venezuela | Bencomo A.,Central University of Venezuela | Lesage J.,University of Lille Nord de France | And 5 more authors.
Surface Engineering | Year: 2012

The present investigation has been carried out in order to study the erosion wear behaviour of WC-Co base thermal spray coatings. WC-12Co and WC-10Co-4Cr coatings were deposited by means of high velocity oxygen fuel (HVOF) thermal spraying. The erosion tests were conducted at impact angles of 30 and 90u using SiC particles of ~50 mm in diameter as erodent, at a velocity of 83.4 m s -1. It has been found that the erosion rate for both coated systems was higher when the test was carried out at an angle of 90°. The through-thickness residual stresses of the coatings, as well as the microstructural characterisation, allowed an explanation of the results and the erosion mechanisms in each case. It has been found that, under the experimental conditions carried out in the present study, the WC-10Co-4Cr coating exhibited a higher erosive wear resistance as compared to the WC-12Co coating. © 2012 Institute of Materials, Minerals and Mining.

Puchi-Cabrera E.S.,Central University of Venezuela | Puchi-Cabrera E.S.,Venezuelan National Academy for Engineering and Habitat | Puchi-Cabrera E.S.,University of Lille Nord de France | Staia M.H.,Central University of Venezuela | And 7 more authors.
Surface and Coatings Technology | Year: 2013

Rotating bending fatigue experiments, both in air and in a 3% NaCl solution, have been carried out in order to study the fatigue behavior of a 7075-T6 aluminum alloy coated with a WC-10Co-4Cr cermet by high velocity oxygen fuel (HVOF) thermal spray, without any grit blasting prior to the coating deposition. The results indicate that the presence of the coating gives rise to a significant increase in the fatigue strength of the substrate and therefore, that from the fatigue behavior point of view this coating could be a feasible replacement of electrolytic hard chromium plating in aircraft applications. Such an increase in fatigue and corrosion-fatigue strength is believed to be associated with the intrinsic microstructural characteristics, corrosion resistance and mechanical properties of the coating, its compressive residual stresses and the possible compressive residual stress field induced in the substrate during coating deposition. The fractographic analysis of the specimens indicates that the final fatigue fracture could be due either to the joint action of a large number of cracks, which propagate from the substrate-coating interface, or to a single dominant fatigue crack, depending on the maximum alternating stress applied to the coated system. It is shown that the lack of grit blasting prior to HVOF deposition does not seem to compromise the functionality of the coated system, while it avoids the introduction of further sharp stress concentrators for the nucleation of fatigue cracks. © 2012 Elsevier B.V.

Chicot D.,University of Lille Nord de France | Puchi-Cabrera E.S.,Central University of Venezuela | Puchi-Cabrera E.S.,Venezuelan National Academy for Engineering and Habitat | Decoopman X.,University of Lille Nord de France | And 3 more authors.
Diamond and Related Materials | Year: 2011

Adhesion and hardness of Diamond-Like Carbon films are improved by nitriding of the steel substrate prior to PVD deposition. Since the mechanical properties of the nitrided steel layer are not homogeneous, i.e. a significant hardness decrease is observed in the upper nitrided layer close to the surface, an outer surface layer of ~ 15 μm is removed prior to the film deposition. In the present work, a 316L stainless steel substrate is nitrided in a cyanide-cyanate solution at 570 °C during 3 h. The coated system involved the deposition of a hydrogenated, amorphous carbon (a-C:H) solid lubricant of ~ 2 μm including a chromium carbide interlayer. The comparison between the hardness behavior of the DLC/steel and the DLC/nitrided steel systems reveals the existence of a very important hardness gap, which highlights the benefit of the nitriding treatment prior to coating deposition. In addition, the microhardness-depth profile is determined from a load-depth curve, by applying a simple hardness model. The predicted change in hardness is found to be in a very good agreement with the experimental profile, which allows the hardness determination both in the white layer and in the diffusion zone over ~ 30 μm in total depth. However, only the composite hardness modeling allows the accurate determination of the intrinsic hardness of the film. © 2011 Elsevier B.V. All Rights Reserved.

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