Sliding wear of a-C:H coatings against alumina in corrosive media

This paper reports the results obtained from the study of friction and sliding wear in two corrosive solutions of an a-C:H coating deposited on 316L stainless against an alumina ball, employed as static counter part. Calculations of the values of the von Mises stresses developed at the coating–substrate interface, as soon as the ball touches the coated sample, and how this state of stress influences the response of the coated system under the corrosion environment, are presented and discussed. The results obtained from these calculations, as well as from the experiments conducted in the present research, are compared with other experiments published in the literature, where a-C:H coatings deposited on different substrates and with different coating architectures were tested in similar corrosive media. It has been determined that in those systems, where the von Mises stress in the coating, found in the vicinity of the interface, exceeds the threshold value of approximately 370MPa, coating failure with spallation will take place, regardless of the substrate nature on which this coating has been deposited. From this analysis it has been concluded that the coating yield strength is of utmost importance in conferring the a-C:H coated system there quired stability in a corrosive solution

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

Sliding wear resistance of thermal sprayed wc-12co coatings reinforced with carbon nanotubes

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

Fatigue behavior of a structural steel coated with a WC–10Co–4Cr/Colmonoy 88 deposit by HVOF thermal spraying

The fatigue behavior of a SAE 4340 steel, coated with a 50% WC–10Co–4Cr/50% Colmonoy 88 deposit, by high velocity oxygen fuel (HVOF) thermal spray, has been investigated. The change in the maximum alternating stress with the number of cycles to fracture has been described by means of the relationship advanced by Stromeyer. A fractographic analysis has been carried out on some representative fracture surfaces, by means of scanning electron microscopy (SEM) techniques. The mechanical properties of the coating were characterized by means of nanoindentation tests. The results indicate that the coating is highly heterogeneous. Its deposition gives rise to a decrease in the fatigue strength of the substrate of ∼ 30%, in comparison with the uncoated substrate. The decrease in fatigue strength is due to the presence of stress concentrators at the substrate–coating interface, as well as the intrinsic characteristics of the coating

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

Incremental constitutive description of SAE 5120 steel deformed under hot-working conditions

International audienceThe present communication describes the development of a novel incremental formulation for the determination of the flow stress of austenite, as a function of microstructure and deformation conditions. The proposed constitutive description is validated by employing the flow stress curves derived from axisymmetric compression tests performed with samples of a SAE 5120 steel, both under constant and transient deformation conditions. The hot-working response of this structural steel grade has been analyzed in the temperature range of 850°C to 1200°C, at strain rates in the range of 0.01 to 10 s−1. Under most deformation conditions dynamic recrystallization occurs and the evolution of the volume fraction recrystallized has been determined by an appropriate incremental form of the Johnson-Mehl-Avrami-Kolmogorov equation. The work-hardening rate of the material in the work-hardening and dynamic recovery transient has been described by an equivalent incremental form of the original differential equation advanced by Estrin and Mecking. It has been shown that this novel approach allows a very precise description of the experimental values of the flow stress of the material during deformation under constant deformation conditions, as well as the trend followed by this parameter under transient loading conditions. The latter analysis is conducted on the basis of the H parameter indicated by Abbod and co-workers. It has been determined that hot working of this steel grade at low temperatures in the austenitic range, followed by cooling to room temperature at moderate rates, leads to a significant refinement of the ferrite-pearlite microstructure, with ferrite grain sizes of less than 10 µm

Plausible extension of Anand's model to metals exhibiting dynamic recrystallization and its experimental validation

International audienceModeling and optimization of industrial hot-working operations by means of commercial finite element computer codes require robust constitutive descriptions, which could be easily implemented. Also, it is expected that such formulations are able to describe as accurate as possible the flow stress, work-hardening and work-softening rate of the material, as a function of microstructure and deformation conditions. The present communication describes the development of a novel constitutive description of metals which exhibit dynamic recrystallization during deformation under hot-working conditions. The formulation is founded on the extension of the model earlier developed by Anand and co-workers for the constitutive description of metals which exhibit dynamic recovery as the only dynamic restoration mechanism during hot deformation. The advanced constitutive formulation has been validated by conducting axisymmetric compression tests with samples of a R260 steel employed for the manufacture of rail tracks. The specimens were deformed in a wide range of temperatures and strain rates, both under constant and variable strain rate conditions. The latter involve either an increase or a decrease in the Zener-Hollomon parameter as plastic deformation is applied. The results obtained indicate that the proposed constitutive description is able to reproduce quite accurately the experimental flow stress data. It has also been shown that the correct computation of the recrystallization time and volume fraction recrystallized dynamically, by means of an appropriate differential or incremental formulation of the Avrami equation, constitutes an essential aspect of the model. Such an approach is particularly important for predicting correctly the changes in flow stress under variable strain rate conditions

Fatigue performance of a SAE 1045 steel coated with a Colmonoy 88 alloy deposited by HVOF thermal spraying

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Measurement of residual stress in thermal spray coatings by the incremental hole drilling method

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