A re-appraisal of the dusty gas model.

Experimental measurements have been made of gaseous diffusion and flow in porous materials of metallurgical relevance. Hollow spheres of the porous materials, prepared by isostatic compaction, sintering and reaction, have been placed in an apparatus able to maintain gases of known composition and pressure inside and outside the spheres. Two separate types of experiment were carried out. In the first set, the permeation of pure gases across the spheres was determined at a range of different total pressures. In the second set, the counter diffusion of two gases was studied at a single mean pressure but under a range of different pressure gradients. Measurements made with a zero pressure gradient - isobaric experiments - constituted a key component in these binary diffusion experiments. Experiments were conducted at high and low temperatures using helium, argon, carbon dioxide and nitrogen and in porous iron produced by reduction, in sintered porous iron and in lime produced by the decomposition of calcium carbonate. The experiments were analysed in terms of the Dusty Gas Model, a fresh development of this model being presented to emphasise its phenomenological nature and include a general statement of the influence of mechanically driven gas flows. The standard application of these equations is used to analyse the single gas permeability experiments and thus to determine the Knudsen diffusion coefficient and a parameter quantifying the porous material's resistance to mechanically driven gas flow. A new unified method of solution is then introduced for binary diffusion, combining a previously obtained solution for isobaric diffusion with a new analysis for non-isobaric diffusion and flow. Using this method, a parameter determining effective binary molecular diffusion coefficients has been obtained from the isobaric experiments and used to predict non-isobaric diffusion rates, these predictions being compared with the corresponding experimental results. Further development of the method has allowed it to be applied to the non-isobaric equi-molar counter diffusion process that occurs during the reduction of hematite and to non-isobaric diffusion during the decomposition of calcium carbonate

Recubrimientos nanoestructurados de circonia estabilzada con itria (ysz) depositados mediante técnicas de termorrociado por plasma en suspensión

Las propiedades de los recubrimientos a base de circonia estabilizada con ytria (YSZ) les confieren un excelente desempeño como barreras térmicas (TBC). En el presente trabajo, recubrimientos de 8YSZ fueron depositados sobre Haynes 230 mediante el proceso de termorrociado por plasma por suspensión (SPS) con el fin de servir de enlace (subcapa) entre el sustrato y un recubrimiento más grueso de YSZ, depositado por termorrociado por plasma atmosférico (APS). Se estudió el efecto del espesor de la subcapa depositada por SPS y la influencia de los tratamientos térmicos posteriores (TT) a 300°C y 600°C sobre su desempeño tribológico a temperatura ambiente (Tamb) y 650°C, respectivamente. Durante los ensayos de desgaste deslizante con una carga de 2 N contra alúmina, se determinó que la reducción del espesor del recubrimiento de 75 μm a 25 μm incrementa la resistencia al desgaste aproximadamente 5 veces. Asimismo, para el espesor de 25 μm el TT a la temperatura de 600°C disminuye 6 veces su resistencia al desgaste con respecto a la condición original del recubrimiento. Similarmente, cuando el ensayo se realizó a 650°C, el comportamiento tribológico desmejoró significativamente. Los resultados han sido relacionados con los cambios morfológicos que tienen lugar durante el calentamiento

Modeling the composite hardness of coated systems involving multilayer coatings

The change in the composite hardness with penetration depth derived from nanoindentation tests conducted on coated systems, which involve the deposition of multilayer coatings, in general exhibit a complex shape, as a consequence of the sequential contribution of each coating layer to the composite hardness during indentation loading. In spite that there are a number of models, which have been proposed for describing the change of the composite hardness with penetration depth for monolayer coatings, as well as for determining the coating and substrate hardness, very few research works have addressed the problem of describing this kind of data for multilayer coatings. In the present communication, a rational approach is proposed for extending two models widely used for the analysisof monolayer coatings, in order to describe the composite hardness data of multilayer coatings, as well as for determining the hardness of each individual layer and that of the substrate. Thus, a modified form of the models earlier advanced by Korsunsky et al. [1] and Puchi-Cabrera [2], as well as their computational instrumentation, are proposed. The extension of both models to deal with multilayer coatings is conducted on the basis of the model developed by Iost et al. [3], in order to adapt the Jönsson-Hogmark [4] model to the analysis of indentation data of multilayer coatings. The proposed models are validated employing nanoindentation results obtained from a 2024-T6 aluminum alloy coated with a DLC film, employing electroless NiP as intermediate layer (Fig. 1-2), as well as the results obtained for a ZrN/MoN bilayer deposited onto a 316L stainless steel substrate. The advantages and disadvantages of the different models employed in the analysis are thoroughly discussed

Modeling the composite hardness of multilayer coated systems

The change in the composite hardness with penetration depth derived from nanoindentation tests conducted on coated systems, which involve the deposition of multilayer coatings, in general exhibits a complex shape, as a consequence of the sequential contribution of each coating layer to the composite hardness during indentation loading. In spite that there are a number of models, which have been proposed for describing the change of the composite hardness with penetration depth for monolayer coatings, as well as for determining the coating and substrate hardness, very few research works have addressed the problem of describing this kind of data for multilayer coatings. In the present communication, a rational approach is proposed for extending two models widely used for the analysis of monolayer coatings, in order to describe the composite hardness data of multilayer coatings, as well as for determining the hardness of each individual layer and that of the substrate. Thus, a modified form of the models earlier advanced by Korsunsky et al. and Puchi-Cabrera, as well as their computational instrumentation, are proposed. The extension of both models to deal with multilayer coatings is conducted on the basis of the model developed by Iost et al., in order to adapt the Jönsson–Hogmark model to the analysis of indentation data of multilayer coatings. Such a methodology provides a means of computing the volume fraction of each individual layer in the coating, which contributes to the composite hardness. According to the results obtained, this scheme seems to be general enough to be applicable to different hardness models other than the Jönsson–Hogmark model. The proposed modified models are validated employing nanoindentation results obtained from a 2024-T6 aluminum alloy coated with a diamond-like carbon film, employing electroless NiP as intermediate layer. The advantages and disadvantages of the different models employed in the analysis are thoroughly discussed

Scratch evaluation on a high performance polymer

The authors wish to thank the participating communities, the Laboratory of Mechanics surfaces and materials processing, University Lille for the access and 84 usage of its research facility. Present research is financially sponsored by Found for Scientific Research of the Flemish Community (FWO) and the Ghent University Research Board.The scratching process is a well know concept and is usually defined as a kind of surface abrasion, where plastic deformation is promoted by relative friction between soft phase and a hard intender. It is necessary to reduce material loss to minimum or even to reach zero to have an efficient and effective functionality of the materials. Polymers being highly sensitive to wear and scratch damage, their various modes of deformation such as, tearing, cracking, delamination, abrasive and adhesive vary with a narrow range of contact variables like applied normal load, sliding velocity, interfacial lubrication and testing temperature. This is particularly important when these materials are used to improve the tribological performance by adding various types of fillers such as, carbon fibers, graphite,PTFE, TiO2, and ZnS are added. The polymers with nanocomposites have the advantages over micro- composites from the viewpoint of wear and scratch damage, the underlying mechanism of damage in the single asperity mode is still unclear. The goal of this study is to experimentally evaluate the deformation modes and the friction processes involved during the scratching of polymer reinforced with nanocomposites. The scratches were produced on the semicrystalline polyetheretherketone (PEEK) surface using a Rockwell C diamond indenter was pressed onto the flat surface of each sample, until a complete loadindentation depth-curve was achieved. These scratched surfaces were assessed with optical microscope and scanning electron microscope (SEM) for prevailing deformation mechanism and the geometry of damage

Comportamiento mecánico y la corrosión de aceros de herramientas nitrurados y recubiertos con PAPVD.

In recent years, surface engineering has been employed for the optimization of coated systems, as well as other surface treatments, by means of plasma-assisted technologies. Hard coatings obtained both by PAPVD and PACVD can improve significantly the surface properties of the substrate in terms of its mechanical properties and corrosion resistance. Coatings are an integral part of the expansion of new surface engineering technologies. Therefore, the surface engineering field seeks the development of new techniques and materials in order to optimize such coated systems. The ultimate aim is to provide them with the required microstructural features to ensure suitable surface properties and to increase the life of industrial parts and components. This paper presents the main results of the characterization of the mechanical properties and corrosion resistance of a TiN and TiAlN coatings deposited onto D2 and H13 tool steels by PAPVD. The steel substrates were employed both in their original condition, as well as after nitriding.En los últimos años, la ingeniería de superficie ha venido optimizando los sistemas recubiertos y tratamientos superficiales mediante la aplicación de tecnologías asistidas por plasma. Tanto los recubrimientos duros obtenidos por PAPVD como PACVD pueden proveer una mejora significativa en las propiedades superficiales del substrato en términos de sus propiedades mecánicas y resistencia a la corrosión. Los recubrimientos hacen parte integral del desarrollo de nuevos materiales y se busca desarrollar técnicas y materiales que permitan optimizar los sistemas para conferirles las características microestructurales que garanticen el perfil de propiedades idóneo para mejorar la eficiencia e incrementar la vida útil de los componentes industriales y dispositivos. Por lo tanto, este trabajo presenta los resultados de la caracterización de sistemas recubiertos a base de TiN y TiAlN obtenidos mediante deposición física en fase vapor asistida por plasma (PAPVD), en cuanto a su comportamiento mecánico y frente a la corrosión, cuando se utilizan como substrato los aceros de herramienta D2 y H13, tanto en su condición original como nitrurados

Mechanical characterization of coated systems involving multilayer films

The computation of the elastic contact stresses and particularly the detemination of the change in the von Mises stress from the surface of a coated system, when it is subjected to spherical indentation, constitutes an important aspect of the tribological performance assessment of such system

Increase of the load carrying capacity of aluminium 2024-T3 by means of a NiP-CRC-DLC coating

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

Scratch evaluation on a high performance polymer

The authors wish to thank the participating communities, the Laboratory of Mechanics surfaces and materials processing, University Lille for the access and 84 usage of its research facility. Present research is financially sponsored by Found for Scientific Research of the Flemish Community (FWO) and the Ghent University Research Board.The scratching process is a well know concept and is usually defined as a kind of surface abrasion, where plastic deformation is promoted by relative friction between soft phase and a hard intender. It is necessary to reduce material loss to minimum or even to reach zero to have an efficient and effective functionality of the materials. Polymers being highly sensitive to wear and scratch damage, their various modes of deformation such as, tearing, cracking, delamination, abrasive and adhesive vary with a narrow range of contact variables like applied normal load, sliding velocity, interfacial lubrication and testing temperature. This is particularly important when these materials are used to improve the tribological performance by adding various types of fillers such as, carbon fibers, graphite,PTFE, TiO2, and ZnS are added. The polymers with nanocomposites have the advantages over micro- composites from the viewpoint of wear and scratch damage, the underlying mechanism of damage in the single asperity mode is still unclear. The goal of this study is to experimentally evaluate the deformation modes and the friction processes involved during the scratching of polymer reinforced with nanocomposites. The scratches were produced on the semicrystalline polyetheretherketone (PEEK) surface using a Rockwell C diamond indenter was pressed onto the flat surface of each sample, until a complete loadindentation depth-curve was achieved. These scratched surfaces were assessed with optical microscope and scanning electron microscope (SEM) for prevailing deformation mechanism and the geometry of damage

Surface Modification Technologies

The present work has been conducted in order to assess the mechanical and tribological performance of a ZrN coating deposited onto a H13 steel substrate by means of a closed field unbalanced magnetron-sputtering ion-plating (CFUMSIP) process. The hardness and elastic modulus of the coated system have been determined by means of nanoindentation techniques. Dry and wet sliding wear tests, employing a tribometer under a ball-on-disc configuration, were carried out making use of an alumina ball as counterpart, with an applied normal load of 2 N at a constant speed of 5 cm/s. For the wet wear tests, a 3.5 wt% NaCl solution was used. The resulting wear scars were analyzed by means of both SEM and optical profilometry techniques. It has been determined that, during testing under the corrosive solution, the coating experiences a severe abrasive wear mechanism, due to the combined action of the alumina ball, the hard “debris” and the phenomenon of crevice corrosion. On the other hand, it has also been shown that the coated system is able to increase the wear resistance of the substrate by more than one order of magnitude, if the wear tests are carried out in air under the same conditions