An investigation of the effect of metal counterface composition on the tribological performance and behaviour of a PTFE filled polymer composite using surface analysis techniques. / The high specific strength, chemical resistance and processability of polymer composites have made them an attractive alternative to traditional metals and ceramics in many industries. For tribological applications, polymer composites also have the ability to eliminate the need of lubricants and lower maintenance costs. The use of carbon fiber, carbon black and polytetrefluoroethylene (PTFE) are well established in the literature as effective reinforcement agents and solid lubricants respectively but not many studies have explored the tribochemical interactions that occurs during sliding. This study investigates the tribochemical interactions between a polyphenylene ether (PPE) and high impact polystyrene (HIPS) blend based composite and different metal surfaces. Four common metals used in industry were chosen for this study: carbon steel C1018, naval brass 485, Inconel 625 and stainless steel 316. In order to isolate the effect of tribochemical interactions between the polymer composite and counterface metals, consistent pressure and velocity (PV) settings were used for all tests. Frictional forces and temperature data were recorded during testing and the wear rates were determined by weighing samples before and after testing. The polymer sand metal washer surfaces were then examined under scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) for their PTFE surface morphology and transfer film composition, respectively. The surface roughness of both polymer and metal samples were also measured. It was observed that tribological performance of the polymer composite was affected by the composition of the metal counterface, and each metal had a different tendency to operating in a stable and unstable state. The surface morphology of the PTFE phase and the transfer film composition on the metal washers also differed between each polymer-metal system. SEM micrographs reveal agglomeration of PTFE domains on the polymer surface and each system had a different domain size distribution and PTFE surface coverage. The polymer-brass system was found to be the most consistent and give the most stable operations with the highest PTFE coverage on the polymer sample’s surface due to brass’ relatively high reactivity. This was explained by tribochemical reaction that occurs at the interface and the reactivity of each metal alloy. Adhesion must be high in order to enable a thicker and more uniform transfer film to adhere, which provides a smooth asperity-free surface for the polymer to slide against, resulting in a stable and low wear operation. A reactive interface allows the introduction of carboxyl groups on both the surfaces and increase electrostatic adhesion between the polymer transfer film and metal surface. Overall, the reactivity of each metal alloy correlated well with the number of stable tests that each polymer-metal system demonstrated as well as the resulting surface coverage of PTFE. This was taken as evidence of the tribochemical interactions. / Thesis / Master of Applied Science (MASc) / The field of friction, wear and lubrication, also known as tribology, traditionally focuses on metal and ceramic components that have high maintenance and lubrication costs. In recent years, there has been growing interest in plastic composites as a replacement material for tribological applications. The high strength, light weight, chemical resistance and self-lubricating properties of these plastic composites makes them an attractive substitute for metals and ceramics. Understanding the chemical interaction between plastic and metal during sliding is necessary to exploit their properties and performance for specific applications. In this study, a plastic composite based on a blend of polyphenylene ether (PPE) and high impact polystyrene (HIPS) filled with polytetrafluoroethlyene (PTFE), carbon black and carbon fiber was used to investigate the effects of different metals on tribological performance and behaviour. Four common metals used in industry were chosen for this study: carbon steel C1018, naval brass 485, Inconel 625 and stainless steel 316. The tribology tests conclusively showed that friction and wear results differ between polymer-metals systems, with each system displaying a stable and unstable behaviour. Surface analysis revealed that the surface PTFE morphology of the polymer composite and the transfer film composition on the metal washer also differ between metals. Tribochemical reactions and the reactivity of each metal explained the results and behaviour of each polymer-metal system.

Este estudo se propôs a analisar os efeitos das diferentes larguras temporais de pulso do laser de Er:YAG na rugosidade superficial, na perda de volume do material e na altura do degrau formado em uma Y-TZP (Yttrium-stabilized Tetragonal Zirconia Polycrystal) pré-sinterizada. Foram utilizados 5 blocos de Y-TZP pré-sinterizados destinados ao uso CAD/CAM que foram seccionados, obtendo-se 63 espécimes padronizados. Em seguida, esses espécimes foram lixados com uma sequência decrescente de lixas para padronização da superfície. Os grupos experimentais foram compostos a partir de 1 fator de variação - o tratamento de superfície. Os espécimes foram irradiados com o laser de Er:YAG (Fidelis III Fotona, Eslovênia) - 2,94 ?m, 100 mJ, 15,87J/cm2, 10 Hz, 1W, 7 mm, 60% água/40% ar. Assim formaram-se 7 grupos experimentais (n=9): G1 (50 ?s); G2 (100 ?s); G3 (300 ?s); G4 (600 ?s); G5 (1000 ?s); G6 (Abrasão triboquímica com partículas de 30 ?m); G7 (Sem tratamento). Após os tratamentos de superfície, os espécimes foram sinterizados em forno específico, de acordo com as recomendações do fabricante. Foram capturadas imagens em Microscópio Confocal a Laser 3D de cada espécime e avaliadas por meio de um software. A análise dos grupos irradiados revelou um aumento da rugosidade nos grupos G1, G2, G3 e G4 quando comparados aos grupos G6 e G7. O grupo G5 apresentou superfície totalmente plana e desfavorável para retenção. No que se refere à perda de volume e formação de degrau, os grupos G1, G2 e G3 demonstraram grande perda de volume e grande altura de degrau formado, o que pode levar a uma desadaptação da peça protética. No grupo G4 foram observados valores de rugosidade satisfatórios com pouca perda de volume e pequena altura de degrau formado, semelhante ao que foi notado para a abrasão trioboquímica (G6), podendo ser indicada para tratamento de superfície de Y-TZP pré-sinterizada. A irradiação com o laser de Er:YAG promoveu um padrão morfológico com muitas irregularidades, característico de ablação para os grupos G1, G2, G3 e G4 e, para todos os protocolos utilizados, não foi observada a presença de trincas ou carbonização. Sugere-se que a largura temporal de 600 ?s (G4) seja a mais indicada como alternativa para tratamento de superfície, objetivando a criação de micro-retenções superficiais, com pouca perda de volume de material e que, ao mesmo tempo, não provoque danos à estrutura da cerâmica policristalina. / This study evaluated the effects of different Er:YAG laser pulse width protocols on surface roughness, loss of volume of the material and the step height formed of pre-sintered Yttrium-stabilized tetragonal Zirconia Polycrystal (Y-TZP) by three-dimensional profilometric assessment. Blocks of pre-sintered Y-TZP were cut providing 63 standard 5mm thick samples which were divided by surface treatment, as follows (n=9): G1 (50?s); G2 (100?s); G3 (300?s); G4 (600?s); G5 (1000?s); G6 (tribochemical silica coating); G7 (Untreated). Laser settings: The Er:YAG laser (Fidelis III; Fotona, Ljubljana, Slovenia) 100mJ, 15,87J/cm2, 10Hz, 1W, (60%) and air (40%) cooling. After treated or not, samples were sintered according to the manufacturer\'s recommendations. Roughness, volume loss and step and were analyzed by 3D profilometric assessment with confocal laser microscopy. Irradiated groups showed an increased roughness in the groups G1, G2, G3 and G4 when compared to G6 and G7 groups. The G5 group showed a completely flat and unfavorable surface for retention. The groups G1, G2 and G3 shown great loss of volume and the step height formed, which can lead to a gap on the crowns. In G4 were observed satisfactory roughness with little loss of volume and the step height formed similar to G6. Irrespective of laser protocol, any of the specimens showed presence of cracks and carbonization. It is suggested that the pulse width 600?s (G4) is the most suitable pulse width protocol as an alternative surface treatment, promoting micro-retention, with little loss of volume of material, comparable to gold standard treatment.

This diploma work is performed at Sandvik Mining and Rock Technology, Rock Tools division, a world-leading mining equipment manufacturer. The aim is to study the wear of cemented carbide rock drill inserts worn against granite and sandstone countersurfaces, with focus on the impact of binder phase composition and flushing agent chemistry. A brief introduction to rock drilling, cemented carbides and the wear and degradation mechanisms of cemented carbides in rock drilling is given. Wear is induced in a lab test by sliding cemented carbide inserts against granite and sandstone countersurfaces while flushing with deionized water or synthetic mine water. The wear is quantified by measuring material weight loss, and worn inserts are studied by SEM. All wear marks feature crushed, fragmented and heavily deformed WC grains and cavities left after individually removed WC grains. Rock adhere strongly on inserts worn against both granite and sandstone, and adhered material from both rock types sometimes endure the mechanical contact between insert and rock without significant spalling. Inserts tested with deionized water against sandstone wear 2.2 - 5.1 times more relative to against granite, and the only distinct difference observed is the distribution of adhered rock. The use of synthetic mine water relative to deionized water impacts the wear of all inserts, though corrosion products are only found on some of them. Further, the tribological contact greatly impacts the corrosive attack. The relative wear difference using different water chemistries is larger for inserts with a smaller relative amount of binder. In most cases, increased wear is measured for inserts tested with synthetic mine water. For reasons yet unknown, this trend is reversed for inserts with a high relative amount of binder tested against sandstone, where a decrease in wear is measured instead. / Detta examensarbete har utförts åt Sandvik Mining and Rock Technology, Rock Tools avdelningen, som är en världsledande utrustningstillverkare inom gruvindustrin. I arbetet undersöks nötningen av så kallade bergborrstift av hårdmetall. Berg är generellt ett mycket hårt och sprött material, och borrning i berg går därför i huvudsak ut på att krossa och spola bort krossad sten. Längst fram på bergborrar sitter borrkronor som till största del är gjorda i stål. Då stål är för mjukt för att effektivt kunna avverka berg monterar man in stift av hårdmetall längst fram på borrkronan. Hårdmetall är ett kompositmaterial av mycket hårda men spröda wolframkarbidkorn (WC) som hålls ihop av en, jämfört med WC, mjuk och formbar metall som kallas bindefas. Resultatet är ett mycket hårt men fortfarande relativt segt material som dessutom klarar de mycket höga temperaturer som uppstår vid bergborrning. Traditionellt används kobolt som bindefas, men nu tros det finnas hälsorisker med kobolt och dessutom sker en stor del av världens koboltutvinning under oetiska förhållanden i konfliktländer i Afrika. Detta i kombination med att koboltpriserna ökat dramatiskt de senaste åren leder till att man nu söker efter alternativa bindefaser. Bland annat undersöker man olika legeringar av nickel och järn. I detta arbete jämförs nötningen av stift med nickel-, järn- och olika koboltbindefaser. I ett labtest fås nötning genom att stiften trycks mot en roterande stencylinder av antingen granit eller sandsten. I verkliga förhållanden används ofta så kallat gruvvatten som sipprar in i gruvan som spolvatten för att ta bort stenkrosset och kyla borrkronan. För att se hur kemin i spolvattnet påverkar nötningen spolas kontaktytan mellan stift och stencylinder med antingen avjoniserat vatten eller syntetiskt gruvvatten under testerna. Stiftens materialförlust under provningen beräknas genom att mäta deras vikt innan och efter. För att se om skillnader i nötningshastighet mellan olika stifttyper eller testvillkor avspeglas i olika utseenden på slitytorna undersöks stiften med hjälp av ett svepelektronmikroskop (SEM). Från SEM-bilderna ser man att alla stift från alla testvillkor har krossade och fragmenterade WC-korn på ytan och att stora delar av slitytorna täckts av påkletat berg. Bergpåsmetningarna är ibland mycket tunna (< 1 μm) och delvis inblandade i bindefasen, och ibland betydligt tjockare (flertal μm). De tjockare påsmetningarna är bundna så pass hårt till ytan att de kan upprätthålla delar av kontakten mellan stiftet och berget under testningen utan att lossna. Huruvida detta skyddar hårdmetallen från att nötas eller om det påkletade berget reagerar med, och därmed ökar den kemiska nedbrytningen av stiftet är inte utrett. Berget skyddar dock den underliggande hårdmetallen mot den korrosion som uppstår i kontakt med spolvattnet. Resultaten visar att stiften nöts betydligt mer mot sandsten än mot granit. Förutom att bergpåsmetningarna har en annan fördelning över ytan så syns inga tydliga skillnader mellan stiften testade mot de båda bergarterna. De flesta stiften nöts mer när de testas med gruvvatten än med avjoniserat vatten. Detta gäller alla stift utom de som har hög relativ mängd bindefas och som testats mot sandsten. Dessa stift nöts tvärt om mindre när de testas med gruvvatten än med avjoniserat vatten. Hittills har ingen anledning till denna konsekventa avvikelse hittats.

When loss of material due to sliding of two solids is promoted/prevented, in the presence of chemically reacting liquid or gas, tribochemical wear is said to occur. Tribochemical wear, in which corrosive media promotes material loss, is a serious concern in a variety of applications like machining, bio-implants, gas turbine engines etc. The most pervasive corrosive media encountered in applications are water and air. Air also contains water vapour along with oxygen, both of which adsorb and react with most materials, thus influencing their wear behaviour. The need for higher operating temperatures and compression ratios in gas turbine engines require development of high temperature wear resistant coatings to protect their soft metallic components. Ti based nitride coatings with Ti, Al, Si, Cr, Ta, Nb, V are known for wear resistance because of their high hardness which is second only to diamond and c-BN. High O affinity of these elements, induce the coatings to form passive oxide scale up to reasonably high temperatures and offer superior corrosion and oxidation resistance. However, sliding can remove the passivating layer, exposing the native surface to the environment which can lead to enhanced tribochemical wear. Oxidation resistance under static conditions does not guarantee low tribochemical wear; however, the tribochemical reactions causing the corrosion are of interest. Another concern is that sliding in unison with high temperatures can activate processes like enhanced diffusion, phase transformations in nitride coatings as well as in the substrate. Hence one of our objectives is to perform wear tests at high temperatures to understand the dominant mechanisms that affect wear in nitride coatings. Wear tests in the range of room temperature up to the oxidation limit of these coatings are designed.In this study TiN and high aluminium containing TiAlN coatings are chosen to study understand the wear behaviour as function of temperature up to 800°C [1]–[3]. In order to study wear of coatings, it is necessary to identify the best possible materials and methods. Though under the targeted application the coatings have to perform under fretting tests, pin on disk configuration is used which simplifies the analysis and gives deeper insight into the wear mechanism. Coated ball is used as the pin which is stationary unlike many earlier studies where the coating is applied on the rotating disk. The purpose of keeping the pin stationary is to minimize the counter-face wear and, instead, accelerate wear in these hard coatings. This method also enables easy and accurate measurement of wear depth and volume by using an optical microscope, while the conventional coated disk method requires profilometry and statistically sound measurements. To enable coating performance, substrate should not undergo much loss of strength before 800°C and hence aerospace grade IN718 alloy is chosen as the substrate which softens slowly beyond 650°C. Alumina is used as counter-face, since it has high hardness, excellent mechanical, chemical and thermal stability. In the current study, TiAlN coating is tested for wear in the range of room temperature to 800°C. Figure 1 represents the data obtained from the wear experiments. It is found that the wear is higher with large scatter at room temperature while it remains constant from 200- 750°C. Two important observations are made, firstly that the TiAlN is susceptible to some kind of a corrosive wear at room temperature which depended on the timing of the tests and secondly that the coating shows a surprisingly constant wear behaviour over the temperature range of 200-750°C. The scatter at room temperature is found to be linked with seasonal fluctuation of humidity which is verified by performing tests under controlled humidity conditions. Water vapour and oxygen are potential reacting gases present in air. Oxidation and oxidative wear is known to occur in many materials as temperatures increase which seem to be linked to thermal activation of oxidation. However lower wear at 200°C and above compared to room temperatures suggests something else to be happening .It is evident then that between room temperature and 200°C lies a transition of some kind in the tribochemical reaction which is responsible for the observed wear behaviour of TiAlN. A detailed study to understand this transition is then undertaken for the composition of TiN coatings so that benchmarking and comparison with TiAlN is possible. Also if the wear behaviour of TiN is found similar to TiAlN then it would indicate a general phenomenon which can be extended to Ti based nitrides. Figure 1 Wear rate as a variation of temperature for TiAlN coatings In contrast to low temperature wear behaviour of TiAlN, a constant wear in the range of 200-750°C is surprising because the primary suspect which is oxidation is thermally activated. The oxide scale though expected to be thin at low temperatures, has to increase in thickness with temperature due to increased diffusion and reaction rates. The oxide scale also undergoes a change in morphology and composition which indicate a lower oxidation resistance as temperature increases. A preliminary characterization of the wear scar on the ball shows that the oxide inside the worn region is thinner than the oxide outside at 750°C. The amount of O within the wear scar is similar to levels observed on as deposited surface while the surface outside the wear scar shows oxidation and discolouration. The results suggest that oxidation inside worn region at high temperatures might be slower than the expected parabolic oxidation occurring outside the wear region. It is speculated that a double layer oxide is formed with TiO2 towards the surface and Al2O3 towards the nitride which is responsible for the lower wear at high temperature. This is supported by the fact that larger amount of Ti is found in the wear debris as temperature inceases. Superficial surface cracks appear at higher loads at temperatures as low as 600°C but they affect wear only above 800°C due to substrate softening. This shows that the coatings are still limited by the substrate softening temperature and could be used at higher temperatures. Tribo-reaction in metals, nitrides and carbides can be brought about in the presence of O2 or water vapour. Tribochemical wear of SiN, SiC, TiN, TiAlN, alumina and most other ceramics at room temperature are found to depend on humidity[4]–[6]. But only tribo-oxidation due to O2 is found to operate at high temperatures[7], [8]. Notwithstanding, it is known that SiC and SiN are more resistant to attack from O2 above 800°C than from steam. Hence the role played by water vapour is found to be convoluted. Moreover, relative humidity is the frequently mentioned quantity with regard tribochemical wear at room temperatures. It should be noted that relative humidity is not a measure of chemical activity of water vapour. Rather the water vapour pressure which represents the chemical activity of water, is not given much importance in the earlier studies. In this study, the importance of humidity, water vapour pressure and temperature in influencing wear, is studied by performing controlled wear tests on TiN. To explore the effect of temperature and water vapour pressure, TiN is tested varying temperature range of 28 °C to 90°C and water vapour pressure in the range of 3-35 mm-of-Hg. Wear tests are conducted keeping temperature constant with varying water vapour pressure and vice versa. The results show that, wear increased with humidity/vapour pressure at a fixed temperature but wear dropped drastically with increase in temperature at constant vapour pressure up to a critical temperature beyond which wear remained constant. This is one of the major unexpected findings since temperature is expected to increase wear volume. Also the critical temperature is found to shift to higher temperatures as water vapour pressures increased. It was suspected that capillary condensation was playing a role in the wear which was later verified. The whole wear behaviour is shown to be correlated with the amount of capillary condensed water. The large radius of curvature of the asperities on the polished coating surface and the smooth surface formed on the counter-face due to debris compaction form conditions favourable for capillary condensation. Any two hydrophilic surfaces which come in contact can form capillary condensation to occur at the cusps formed around the contact. However a threshold pore size of about 1nm existed below which condensation did not influence wear. Another observation is that the water vapour did not affect wear significantly in the absence of condensation for TiN coatings. As temperatures increased condensation became unfavourable, but the high vapour pressure present showed no signs of wear enhancement. This is surprising and unexpected compared to earlier reports.[9], [10] On contrary tests in liquid water showed expected behaviour for tribochemical reaction i.e wear increased with temperature. The wear in liquid water is highest when compared studies in air at any given temperature. The X-ray electron emission spectroscopy (XPS) analysis is performed to understand the surface reactions. It appears that O2 forms a barrier oxide which protects the nitride from reacting with water vapour. However when condensation occurs or in water, the oxygen and water collude into forming softer hydroxide layer which is easily removed. Though chemically water and water vapour are same, they affect wear in TiN very differently. Summarising the synopsis, exploration into high temperature wear of TiAlN reveals that it can handle oxidative wear upto 750°C showing constant wear over the temperature range of 200-750°C. Reduction in residual stresses and substrate softening may be responsible for higher wear at higher loads since the cracking is observed at 5N is absent at 3N. The substrate is expected to soften above 650°C but this does not necessarily affect wear until the load is increased or the temperature is sufficiently high. However TiAlN and TiN coatings showed susceptibility to tribo-corrosion in water and high humidity at room temperature. At high humidity, condensation of water leads to increase in wear. The dependence of wear on humidity is found to be because of capillary condensation. The negligible dependence of wear on humidity in the absence of condensation is ascribed to formation of oxide layer due to reaction with O2 and coating. The oxide barrier formed due to atmospheric O2 protects the coating from reacting with the water vapour. The oxide barrier on TiN forms faster indicating O2 reaction to be faster than the reaction with water vapour. In the presence of capillary condensation or water, O2 is depleted from contacting surfaces thus hindering the formation of the barrier oxide, increasing wear. As temperature increases the condensation becomes unfavourable and barrier oxide dominates the wear mechanism upto high temperatures which is dominated by oxidative wear.

Este estudo se propôs a analisar os efeitos das diferentes larguras temporais de pulso do laser de Er:YAG na rugosidade superficial, na perda de volume do material e na altura do degrau formado em uma Y-TZP (Yttrium-stabilized Tetragonal Zirconia Polycrystal) pré-sinterizada. Foram utilizados 5 blocos de Y-TZP pré-sinterizados destinados ao uso CAD/CAM que foram seccionados, obtendo-se 63 espécimes padronizados. Em seguida, esses espécimes foram lixados com uma sequência decrescente de lixas para padronização da superfície. Os grupos experimentais foram compostos a partir de 1 fator de variação - o tratamento de superfície. Os espécimes foram irradiados com o laser de Er:YAG (Fidelis III Fotona, Eslovênia) - 2,94 ?m, 100 mJ, 15,87J/cm2, 10 Hz, 1W, 7 mm, 60% água/40% ar. Assim formaram-se 7 grupos experimentais (n=9): G1 (50 ?s); G2 (100 ?s); G3 (300 ?s); G4 (600 ?s); G5 (1000 ?s); G6 (Abrasão triboquímica com partículas de 30 ?m); G7 (Sem tratamento). Após os tratamentos de superfície, os espécimes foram sinterizados em forno específico, de acordo com as recomendações do fabricante. Foram capturadas imagens em Microscópio Confocal a Laser 3D de cada espécime e avaliadas por meio de um software. A análise dos grupos irradiados revelou um aumento da rugosidade nos grupos G1, G2, G3 e G4 quando comparados aos grupos G6 e G7. O grupo G5 apresentou superfície totalmente plana e desfavorável para retenção. No que se refere à perda de volume e formação de degrau, os grupos G1, G2 e G3 demonstraram grande perda de volume e grande altura de degrau formado, o que pode levar a uma desadaptação da peça protética. No grupo G4 foram observados valores de rugosidade satisfatórios com pouca perda de volume e pequena altura de degrau formado, semelhante ao que foi notado para a abrasão trioboquímica (G6), podendo ser indicada para tratamento de superfície de Y-TZP pré-sinterizada. A irradiação com o laser de Er:YAG promoveu um padrão morfológico com muitas irregularidades, característico de ablação para os grupos G1, G2, G3 e G4 e, para todos os protocolos utilizados, não foi observada a presença de trincas ou carbonização. Sugere-se que a largura temporal de 600 ?s (G4) seja a mais indicada como alternativa para tratamento de superfície, objetivando a criação de micro-retenções superficiais, com pouca perda de volume de material e que, ao mesmo tempo, não provoque danos à estrutura da cerâmica policristalina. / This study evaluated the effects of different Er:YAG laser pulse width protocols on surface roughness, loss of volume of the material and the step height formed of pre-sintered Yttrium-stabilized tetragonal Zirconia Polycrystal (Y-TZP) by three-dimensional profilometric assessment. Blocks of pre-sintered Y-TZP were cut providing 63 standard 5mm thick samples which were divided by surface treatment, as follows (n=9): G1 (50?s); G2 (100?s); G3 (300?s); G4 (600?s); G5 (1000?s); G6 (tribochemical silica coating); G7 (Untreated). Laser settings: The Er:YAG laser (Fidelis III; Fotona, Ljubljana, Slovenia) 100mJ, 15,87J/cm2, 10Hz, 1W, (60%) and air (40%) cooling. After treated or not, samples were sintered according to the manufacturer\'s recommendations. Roughness, volume loss and step and were analyzed by 3D profilometric assessment with confocal laser microscopy. Irradiated groups showed an increased roughness in the groups G1, G2, G3 and G4 when compared to G6 and G7 groups. The G5 group showed a completely flat and unfavorable surface for retention. The groups G1, G2 and G3 shown great loss of volume and the step height formed, which can lead to a gap on the crowns. In G4 were observed satisfactory roughness with little loss of volume and the step height formed similar to G6. Irrespective of laser protocol, any of the specimens showed presence of cracks and carbonization. It is suggested that the pulse width 600?s (G4) is the most suitable pulse width protocol as an alternative surface treatment, promoting micro-retention, with little loss of volume of material, comparable to gold standard treatment.

La zone Segment-Piston-Chemise (SPC) d’un moteur thermique est une source importante de dissipation d’énergie liée au frottement sévère. Il est important d’optimiser les lubrifiants agissant dans cette zone car ils ont un impact essentiel sur la durée de vie des pièces mécaniques et la réduction de la consommation énergétique des véhicules. Le dépôt de revêtements sur certaines pièces soumises à des frottements sévères est également une alternative intéressante, en particulier les revêtements carbonés de type DLC et diamant nanocristallin (NCD). La formulation des nouveaux lubrifiants moteurs doit tenir compte de la présence éventuelle de ces nouveaux matériaux. Dans ce travail de doctorat, l’action tribochimique de nouveaux additifs à base de molybdène, couplés à un additif anti-usure de type ZnDTP et à d’autres additifs de type modificateur de frottement, a été étudiée. Ces derniers sont depuis longtemps connus pour leur grande capacité à réduire le frottement grâce à la formation du composé lamellaire di-sulfure de molybdène (MoS2), notamment les additifs MoDTC dimer. Cependant la quantité importante de soufre qu’ils contiennent reste problématique du fait de son impact néfaste sur l’environnement. L’effet synergique d’un additif au molybdène purement organique, appelé Mo-organique, en combinaison avec un additif ZnDTP et d’une triamine grasse, a été découvert. Ce nouveau mélange ternaire permet de réduire jusqu’à 20% la contenance en soufre d’une formulation lubrifiante globale tout en améliorant les performances tribologiques par rapport à celles du MoDTC classique. De ce fait, une réduction du coefficient de frottement atteignant 50% a été observée. Une caractérisation physico-chimique multi-échelles des tribofilms binaires et ternaires dérivés du Mo-organique a été réalisée en utilisant une approche multi-techniques (XPS, ToF-SIMS, FIB/HRTEM). Un mécanisme réactionnel hypothétique conduisant à la formation du MoS2, passant par un composé intermédiaire de type « thiomolybdate » a été proposé. / The friction in the Piston-ring area is a significant cause of the energy waste. It is important to optimize the lubricants acting in this zone because they have an essential impact on the service life of the mechanical parts and the reduction of the energy consumption of vehicles. The coating on relevant part is also an interesting alternative, such as the carbon coating of the DLC type or a nano-crystalline diamond (NCD) coating. If such coating materials are used, the composition of new lubricants has to be adapted correspondingly. This doctoral work-studies the tribo-chemical action of new additives with molybdenum, coupled with an anti-wear additive of the ZnDTP type as well as with some other friction-modifying additives. Some of these additives, especially the MoDTC dimer, are known to reduce the friction through formation of the lamellar di-sulfur composite of molybdenum (MoS2). However, due to high sulfur content these additives produce significant adverse environmental effects. A synergy effect has been proven of a purely organic molybdenum additive, called Moorganic, combined with a ZnDTP additive and from a fatty triamine. This new ternary mixture allows reducing up to 20% the sulfur content in the lubricant’s global formula and improves the tribological properties in comparison with the classical MoDTC. Consequently, the observed reduction of friction coefficient reached 50%. Using the multi-technic approach (XPS, ToF-SIMS, FIB/HRTEM) we realized a multi-scale physicochemical characterization of the binary and ternary tribo-layers that derived from the Mo-organic. A reactional mechanism that leads to the MoS2 formation has been proposed; it goes through the intermediate composite of the « thiomolybdate » type.