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International audience; Thermal sprayed coatings based on WC-Co are widely used for providing wear resistance to engineering components. The High Velocity Oxygen Fuel (HVOF) thermal spraying technique is one of the most commonly employed for depositing wear resistant coatings on steel substrates and constitutes one of the coating processes that have been technically validated for the replacement of electrolytic hard chrome (EHC) coatings, especially for extreme operating conditions. The present work aims at studying the tribological behavior, under sliding wear conditions, of a coating based on WC-12Co, with and without the reinforcement of carbon nanotubes (CNTs). The coating has been deposited by HVOF thermal spraying on a SAE 1045 substrate steel. Wear tests were carried out under the ball-on-disk configuration, at a constant sliding velocity of ∼ 0.2 m.s-1 and an applied load of 10 N, employing WC-6Co balls as static counterparts. The results for the CNTs reinforced coating have shown a decrease of ∼ 58% and 86% in the values of the average friction coefficient and wear rate, respectively, as compared with the conventional coatings. The observed wear mechanism was mainly of an abrasive type.

An investigation has been conducted in order to determine the effect of both the metallic transfer mode (pulsed arc or short circuit) and the O2 content in the Ar/O2 gas mixture, of the gas-metal arc welding process (GMAW), on the fatigue life under uniaxial conditions of welded joints of 316L stainless steel. It has been concluded that the mixture of the protective gases employed in the process could have an important influence on the fatigue life of the welded joints of such steel in two different ways. Firstly, through the modification of the radius of curvature at the joint between the welding toe and the base metal and, secondly, through a more pronounced degree of oxidation of the alloying elements induced by a higher O2 content in the mixture. As far as the metallic transfer mode is concerned, it has been determined that the welded joints obtained under a pulsed arc mode show a greater fatigue life in comparison with the joints obtained under short circuit for both gas mixtures.Se ha llevado a cabo una investigación con la finalidad de determinar el efecto, tanto del modo de transferencia metálica (arco pulsado o cortocircuito) como del contenido de O2 en la mezcla de gases protectores Ar/O2, del proceso de soldadura a tope mediante arco metálico con protección gaseosa (GMAW), sobre la vida a la fatiga en condiciones uniaxiales de juntas soldadas del acero inoxidable AISI 316L. Dicho trabajo ha permitido concluir que la composición de la mezcla de gases protectores del proceso GMAW pudiera tener una influencia importante en la vida a la fatiga de las juntas soldadas de dicho material, a través de dos formas distintas: primero, mediante la modificación del radio de curvatura entre la raíz del cordón de soldadura y el metal base y, en segundo lugar, a través del mayor grado de oxidación de los elementos de aleación. En cuanto al modo de transferencia metálica, se determinó que las juntas soldadas mediante arco pulsado presentan una mayor vida a la fatiga en comparación con las juntas obtenidas por cortocircuito para ambas mezclas gaseosas.

International audience; The present investigation has been conducted in order to evaluate the tribological behavior of an AA2024-T3 aluminum alloy, coated with a NiP-CrC-DLC coating. The effect of NiP as intermediate layer was evaluated by carrying out calculations using ELASTICA © in order to determine its adequate thickness needed to avoid the plastic deformation of the substrate, ensuring then the integrity of the coating. To evaluate the efficiency of these calculations, a number of dry sliding wear tests were performed employing a ball-on-disk configuration, where alumina balls of 6 mm in diameter were used as counterpart. The sliding wear tests were carried out up to a sliding distance of 800 m, with a normal load of 5 N, a linear speed of 5 cm/s and a contact radius of 3 mm. The wear tracks were analyzed by means of scanning electron microscopy (SEM) techniques coupled with energy dispersive spectroscopy (EDS). The wear volume was determined by means of optical profilometry. The results indicate that, under the present testing conditions, the NiP-CrC-DLC coating exhibits a satisfactory behavior from the mechanical stability point of view when the thickness of the NiP layer is higher than 60 µm, since no surface failures were observed at the end of the tests. For the coated system, the magnitude of the friction coefficient was found to be of approximately 0.1 and that of the wear rate was of about 2.31 ± 0.09 x 10-16 m3/N.m. On the contrary, for the uncoated substrate, the friction coefficient was of approximately 0.5 and the wear rate of 5.46 x 10-13 m3/N.m, that is to say, 3 orders of magnitude greater than that determined for the coated system.

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.