On the use of statistical analysis for tribological evaluation of a solid lubricant

La dégradation des contacts tribologiques sous une sollicitation de fretting est un phénomène complexe lié à l interaction entre deux corps sous une faible amplitude de débattement, ce qui limite la durée de vie des pièces de manière significative. La lubrification solide est de plus en plus utilisée dans les applications tribologiques pour réduire les frottements et protéger la surface du substrat contre l'usure par fretting. La performance du revêtement dépend de nombreux facteurs tels que les conditions de sollicitation, les propriétés du substrat, du contre-corps et du revêtement et l'adhérence entre le revêtement et le substrat. Les objectifs de cette thèse sont de discuter le frottement et le comportement en usure du revêtement sous différentes conditions et d'analyser l'effet des paramètres d essai sur le coefficient de frottement et la durée de vie du revêtement, ce qui peut être effectivement utile pour l'évaluation de la qualité des revêtements. Les tests de fretting sont menés pour comprendre les relations entre le comportement tribologique d'un vernis à base de MoS2 et les conditions d essai. Le revêtement est étudié pour différentes valeurs de force de contact, amplitude de déplacement, configuration de contact, position du revêtement, nature du substrat et épaisseur. L'effet de chaque facteur est évalué par l'analyse de variance. L'analyse de régression est utilisée pour prévoir la performance du revêtement. L'observation de l'évolution de la trace d usure est réalisée pour expliquer l importance des facteurs et les coefficients dans les équations de prédiction. En outre, l'analyse de fiabilité est utilisée pour décrire et prévoir le taux de survie du revêtement sous certaines conditions d essai. Enfin, un modèle linéaire de durée de vie est évalué afin de prendre en compte l'amplitude de déplacement variable.Fretting wear is considered as a complex wear phenomenon related to interaction between two sliding bodies under very low displacement amplitude, which limits the lifetime of elements significantly. Solid lubricant is more and more applied in tribological applications to reduce friction and protect the substrate surface from fretting wear. The performance of coating depends on many factors such as running conditions, properties of substrate, counterbody and coating, and adhesion between coating and substrate. The objectives of this thesis are to discuss the friction and wear behavior of the coating under different running conditions, and to analyze the effect of test parameters on the friction coefficient and lifetime of the coating, which can be effectively helpful for the evaluation of quality of the coating. Fretting experiments are carried out to understand the relationships between the tribological behavior of a MoS2 based varnish coating and running conditions. The coating is investigated under different contact forces, different displacement amplitudes, different contact configurations, different coating positions, different substrates and different thicknesses. The rank of effect of factors is evaluated by the analysis of variance. Regression analysis is used to predict the performance of coatings under certain running conditions. The observation of evolution of wear scar is applied to explain the rank of factor and coefficients in the prediction equations. Furthermore, the reliability analysis is used to describe and predict the survival rate of coatings under certain running conditions. Finally, a linear model for lifetime is assessed in order to take into account variable displacement amplitude.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Development of a friction energy capacity approach to predict the surface coating endurance under complex oscillating sliding conditions

In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent catastrophic consequences. In this study, a model based on local dissipated energy is developed and related to the friction process. Indeed, the friction dissipated energy is a unique parameter that takes into account the major loading variables which are the pressure, sliding distance and the friction coefficient. To illustrate the approach a sphere/plane (Alumina/TiC) contact is studied under gross slip fretting regime. Considering the contact area extension, the wear depth evolution can be predicted from the cumulated dissipated energy density. Nevertheless, some difference is observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter, the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The surface treatment lifetime is then simply deduced from an energy ratio between this specific energy capacity and a mean energy density dissipated per fretting cycle. The stability of this approach has been validated under constant and variable sliding conditions and illustrated through an Energy Density–Coating Endurance char

Behaviour of shot peening combined with WC-Co HVOF coating under complex fretting wear and fretting fatigue loading conditions

This study investigated the fretting and fretting fatigue performance of tungsten carbide–cobalt (WC–Co) HVOF spray coating systems. Fretting wear and fretting fatigue tests of specimens with shot peening and WC–Co coatings on 30NiCrMo substrates were conducted. The WC-Co coating presents very good wear resistance and decreases by more than 9 times the energy wear coefficient (α) under fretting conditions. The tested coating reduces crack nucleation under both fretting and fretting fatigue studied situations. Finally the crack arrest conditions are evaluated by the combined fretting and fretting fatigue investigation. It is shown and explained how and why this combined surface treatment (shot peening and WC–Co) presents a very good compromise against wear and cracking fretting damage

Fretting d'un alliage de titane revêtu et lubrifié (application au contact aube/disque)

La liaison entre aube et disque de fan de turbines aéronautiques est soumise à une sollicitation de fretting. Afin de lutter contre l'endommagement, l'alliage de titane grenaille utilisé est revêtu d'un dépôt plasma rugueux et épais de cu ni in et un film polymère contenant du mos2 (lubrifiant solide) est déposé sur les pieds d'aubes. Le but de la thèse est de comprendre et quantifier l'endommagement de ce contact soumis à des vibrations. Une approche énergétique locale a été développée pour quantifier la durée de vie du lubrifiant solide (définie par l'analyse de l'évolution du coefficient de frottement). Cela permet d'obtenir une courbe maitresse de durée de vie qui peut être utilisée pour prédire la durée de vie du film lubrifiant. Cette approche est stable vis à vis de la géométrie de contact et peut être utilisée pour le choix des revêtements. concernant l'endommagement sans lubrifiant, le critère de fatigue swt a permis d'étudier l'amorcage de fissures en glissement partiel.Fretting occurs in the dovetail contact between the fan disk and blade in aeronautical turbines. In order to prevent fretting damage, the shot peened titanium alloy used is coated with a thick and rough cu ni in plasma layer and a polymer bonded mos2 solid lubricant film is deposited on the roots of the blades. The aim of the thesis is to understand and quantify the damage of this vibrating contact. A local energetic approach is developed to quantify the lifetime of the solid lubricant in the contact (defined through the analysis of the evolution of the friction coefficient). It allows us to obtain a lifetime master curve which can be used to predict the lifetime of the coating. this approach is stable towards the contact geometry and pressure distribution and can be used to compare different coatings. Regarding the damage without solid lubricant, the smith-watson-topper multiaxial fatigue criterion has been used to study the crack nucleation under partial slip condition.LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Surface microstructure of an IN718 3D coating manufactured by Laser Metal Deposition

International audienceLaser Metal Deposition (LMD) is a well-known additive manufacturing (AM) process that offers the ability to repair metal parts, among other benefits. We have focused on IN718 parts that evolve in environments that strongly favor wear. Therefore, a good knowledge of the contact surface microstructure and its properties is necessary to better understand the tribological behavior of these parts. However, the microstructure of the top surface (which is most susceptible to wear) of IN718 coatings deposited by LMD is not particularly well documented in the literature. Most of the studies devoted to this alloy have focused on the study of the cross-sectional microstructure, and the few articles dealing with the top surface microstructure have been devoted to the Laser Powder Bed Fusion (LPBF) process. In this article, four IN718 coatings were successfully fabricated with high density using different scanning strategies. When viewing the microstructure from the top surface, the EBSD map showed a very heterogeneous microstructure with an alternation of fine and coarse grains. It also showed a weak overall texture, but a strong local texture within the fine and coarse grain region. EBSD analysis of the cross-sectional area of the coated section also revealed a microstructure variation along the build direction (BD) with the appearance of small grains between layers after some layers have been deposited. Analysis of both sides of the coated part allowed us to get a better understanding of the final microstructure. We were able to show that this heterogeneous microstructure leads to a spatial variation of the top surface hardness, the pattern of which is directly related to the scanning strategy. Finally, we found that the surface hardness of IN718 LMD samples is higher than that of conventionally produced IN718, which is a promising result in terms of repairing metal parts with good tribological properties

Effect of Spatial Random Distribution of Micro-Contact Areas on the Interfacial Temperature Rise In Fretting.

Peer reviewed: YesNRC publication: Ye

Wear Behavior of Martensitic Stainless Steel in Rolling-Sliding Contact for Planetary Roller Screw Mechanism: Study of the WC/C Solution

The planetary roller screw mechanism is used in the aeronautics industry for electro-mechanical actuators application. It transforms a rotational movement into a translation movement, and it is designed for heavy loads. The main components are made of martensitic stainless steel, and lubricated with grease. Like most usual rolling mechanisms, smearing and jamming can occur before the theoretical fatigue lifetime, especially in poor lubrication conditions. The actuated load is carried by small contacts between the threads of the screw, the rollers and the nut. The static single contact can be described as an ellipsoid on flat contact with high contact pressure (3-4 GPa). The motion consists of rolling with spin associated with side slip up to 10%. The aim of our study is to investigate the wear behavior of the WC/C coated contact for different operating and design parameters such as load, speed and slip ratio. The contact is simulated by a free rolling roller loaded on a rotating disk. A specific apparatus is used to create a contact with a side slip component, i.e. perpendicular to the rolling direction. The wheel rolling speed and the tangential force generated by the slip ratio are measured. The wear behavior of a WC/C carbon-based composite coating is investigated. It reveals progressive wear and cracking in the rolling direction, i. e. perpendicular to the sliding direction. A wear map has been drawn to establish the damage mode depending on the contact conditions

Friction of 316L stainless steel on soft-tissue-like poly(vinyl alcohol) hydrogel in physiological liquid

International audienc

Friction of 316L stainless steel on soft-tissue-like poly(vinyl alcohol) hydrogel in physiological liquid

International audienc

Effect of the elevated temperature on the wear behavior of Laser Metal Deposition IN718 repairs

International audienceIN718, a nickel-based superalloy popular in aerospace, has good high-temperature mechanics/corrosion resistance. Laser Metal Deposition (LMD) repairs using IN718 are extensively explored, yet few studies delve into their tribological aspects. This research examines post-treated IN718 coatings, mimicking rapid repairs, investigating their high-temperature tribological behavior. Samples underwent tribological tests at diverse loads and temperatures. Results show the scanning strategy does not impact the wear behavior. At elevated temperatures, a glaze layer forms in the contact zone, impacting lubrication and surface protection based on its uniformity. Despite its advantageous lubricating ability, at 400°C and 50 N force, the oxidized debris layer lacks mechanical stability. IN718 LMD repairs manifest enhanced high-temperature wear resistance compared to ambient conditions, attributed to the glaze layer