The increasing demand for more readily bio-degradable, renewable and non-toxic environmentally adaptive lubricants with a lower degree of bioaccumulation has escalated the investigation of water-based lubricants as the potential alternatives for conventional mineral-based oils. Water is an excellent environmentally adapted lubricant; however, it is a low viscous fluid and holds downsides of having corrosive nature and extremely low pressure-viscosity coefficient leading to insufficient load-carrying capacity. These shortcomings make pure water a poor choice for operations involving high load and low speed, for instance, within hydropower applications. Therefore, the choice of appropriate modifiers and additives is crucial to improve the viscosity, friction-reducing performance and anti-wear properties of water as a base lubricant. Appropriate selection and combination of bearing materials also significantly improve the tribological performance of the lubricants. In the presented work, tribological behavior of polyvinylpyrrolidone (PVP) and poly(sodium 4-styrenesulfonate) (PSS) thickening agents with water as a base fluid in the lubrication of pure UHMWPE and SCF reinforced UHMWPE bearing materials has been investigated individually under reciprocating tribometer. The results showed that both PVP and PSS are excellent viscosity modifiers. PVP exhibited excellent friction-reducing and anti-wear performance, while PSS revealed increased wear rates with an insignificant reduction of friction coefficients. This study aims to explore the potential for using newly developed water-based lubricants in the replacement of traditional mineral-based lubricants for hydropower turbine bearings.

The wheel-rail contact is at the core of all research related to vehicle-track interaction. This tiny interface governs the dynamic performance of rail vehicles through the loads it transmits and, like any high stress concentration zone, it is subjected to serious damage phenomena. Thus, a clear understanding of the rolling contact between wheel and rail is key to realistic vehicle dynamic simulation and damage analyses. In a multi-body-system simulation package, the essentially demanding contact problem should be evaluated in about every millisecond. Hence, a rigorous treatment of the contact is highly time consuming. Simplifying assumptions are, therefore, made to accelerate the simulation process. This gives rise to a trade-off between accuracy and computational efficiency of the contact models in use. Historically, Hertz contact solution is used since it is of closed-form. However, some of its underlying assumptions may be violated quite often in wheel-rail contact. The assumption of constant relative curvature which leads to an elliptic contact patch is of this kind. Fast non-elliptic contact models are proposed by others to lift this assumption while avoiding the tedious numerical procedures. These models are accompanied by a simplified approach to treat tangential tractions arising from creepages and spin. In this thesis, in addition to a literature survey presented, three of these fast non-elliptic contact models are evaluated and compared to each other in terms of contact patch, pressure and traction distributions as well as the creep forces. Based on the conclusions drawn from this evaluation, a new method is proposed which results in more accurate contact patch and pressure distribution estimation while maintaining the same computational efficiency. The experience gained through this Licentiate work illuminates future research directions among which, improving tangential contact results and treating conformal contacts are given higher priority. / <p>QC 20130911</p>

Hot stamping of aluminium alloys allows for increased formability, decreased springback and the possibility of integrating age-hardening heat treatments into the process. However, it can be challenging due to the occurrence of material transfer of aluminium onto the tool, as aluminium is prone to adhesion even at low temperatures. Hence, lubrication is always necessary when forming aluminium, but lubricants can still fail, leading to direct interaction between tool and workpiece and thus material transfer. This phenomenon reduces the efficiency of the process, as interruptions are necessary for the refurbishment of the tools. Understanding of how material transfer takes place is important in order to find new or improved solutions, in terms of lubrication and surface engineering, to prevent adhesion. Nevertheless, current research in high temperature tribology of aluminium, mainly in terms of material transfer mechanisms, is very limited, as many of the works focus on lubricated conditions and do not look into the fundamental interactions between aluminium alloys and tool steels. In this context, the aim of this work is to investigate the mechanisms behind the occurrence of aluminium alloy transfer onto tool steel during sliding at high temperature and in dry conditions. A hot-strip drawing tribometer was used to perform tests at room temperature, 300°C, 400°C, and 500°C, directly after solubilizing the aluminium alloy at 520°C. Two different topographies for the tool steel were used: ground and polished. Material transfer characterization was performed mainly through scanning electron microscopy. It was found that grinding marks (ground tool steel) and carbides (polished tool steel) act as initiation sites for the transfer to occur. Temperature plays a role on the growth mechanisms of the transfer films during sliding, as thermal softening of the aluminium alloy is the dominant factor in determining the growth direction of the transfer layers. A growth towards the trailing edge (shearing and smearing of the transferred aluminium) or a growth towards the leading edge (build-up of transferred aluminium, leading to a thicker and more localized transfer material).

High strength aluminum alloys have for a long time been a popular material utilized in the automotive and aerospace sector due to coveted mechanical properties in terms of weight, strength, fatigue, and corrosion. However, tribological mechanisms such as tribo-film formation and material transfer during the metal cutting manufacturing process of aluminum impose significant reduction of machining and tool-life performance. Additionally, environmental aspects associated with metal cutting manufacturing has got more interest and pushed cutting tool development in new directions to meet increased customer demands. One possible way of achieving this, is the implementation and utilization of diamond based cutting tools which has been shown to perform well in machining of high strength aluminum. However, in depth knowledge regarding the tribological properties of diamond based cutting tools is currently lacking. Thus, the aim of this master thesis has been to investigate the refined tribological characteristics and properties of WC-Co cemented carbide cutting tools coated with synthetically grown CVD diamond. Tribological testing methods, such as frictional scratch/sliding, pin-turning, contact-zone temperature measuring, and longitudinal turning have been conducted to acquire extensive amount of research material in the form of test samples and data information. Furthermore, pin-turning tests were performed using a newly developed Tribojan pin-turning equipment and the performance of this was evaluated as a subgoal task. Specimen sample analysis have primarily been performed through LOM and SEM/EDS microscopy techniques. The results acquired from testing, microscopy analysis and data set evaluation have showed promising results in terms of frictional characteristic and material transfer properties regarding CVD diamond coated surfaces. The average CoF of CVD diamond sliding against an Alumec 89 aluminum alloy surface were somewhat lower as compared with similar sliding of a conventional uncoated WC-Co cemented carbide material. Furthermore, the frictional behavior and characteristic of CVD diamond appears to be more consistent and regular over longer sliding distances. The contact interaction between the CVD diamond coated surface and Alumec 89 appears to have a more abrasive nature due to the rough surface structure and material properties of the coating. The corresponding tribo-pair contact interaction with WC-Co cemented carbide shows more adhesive tendencies. Additionally, the contact-zone temperature development during pin-turning is shown to be somewhat lower during CVD diamond/Alumec 89 surface interactions. Regarding material transfer properties, CVD diamond are shown to perform well when interacting with high-strength aluminum. The amount of material adherence is significantly reduced on CVD diamond coated surfaces. During longitudinal turning using CVD diamond coated cutting tools, no significant wear was observed. On the other hand, evidence of both adhesive and abrasive wear was observed during turning using conventional uncoated WC-Co cemented carbide tools. Finally, tribological mechanisms acting during Tribojan pin-turning tests was shown to be relatively comparable with an actual machining operation, which indicate that the testing method perform well as compliment to standard frictional sliding and machining testing. / Höghållfasta aluminiumlegeringar har länge varit ett populärt material inom bil- och flygindustrin på grund av deras eftertraktade mekaniska egenskaper när det gäller vikt, styrka, utmattning och korrosion. Däremot medför tribologiska fenomen, så som tribofilmbildning och materialöverföring under metallskärande tillverkningsprocesser för aluminium, en betydande minskning av prestanda hos utrustning och skärverktygens livslängd. Dessutom har miljöaspekterna i samband med metallskärande tillverkning fått ökat intresse och därmed drivit utvecklingen av skärverktyg i nya riktningar för att uppfylla kundernas ökade krav. Ett möjligt sätt att uppnå detta är att införa och använda diamantbelagda skärverktyg, vilka har visat sig fungera bra vid bearbetning av höghållfast aluminium. Dock saknas det för närvarande djupgående kunskaper om de tribologiska egenskaperna hos dessa diamantbaserade skärverktyg. Syftet med detta examensarbete har därför varit att undersöka de förfinade tribologiska egenskaperna hos WC-Co skärverktyg av hårdmetall belagda med syntetiskt odlad CVD-diamant. Tribologiska testmetoder, så som friktionsskrapning/glidning, pinnsvarvning, temperaturmätning i kontaktzonen samt longitudinell svarvning, har genomförts för att samla in analysmaterial i form av prover och datainformation. Dessutom utfördes pinnsvarvningstesterna med hjälp av en nyutvecklad så kallad Tribojan-utrustning, vars prestanda har utvärderats som ett delmål i projektet. Analyser av provexemplar har huvudsakligen utförts med hjälp av mikroskopitekniker så som LOM och SEM/EDS. Resultaten från provning, mikroskopianalys och utvärdering av data har visat lovande resultat när det gäller friktions och materialöverföringsegenskaper för CVD-diamantbelagda ytor. Den genomsnittliga CoF för CVD-diamant som glider mot en yta av aluminiumlegeringen Alumec 89 var något lägre jämfört med motsvarande glidning av konventionellt WC-Co hårdmetallmaterial. Dessutom verkar friktionsbeteendet hos CVD-diamant vara mer konsekvent och regelbunden över längre glidsträckor. Kontaktinteraktionen mellan ytor av CVD-diamant och Alumec 89 verkar också ha en mer abrasiv karaktär på grund av diamantbeläggningens grova ytstruktur och materialegenskaper. Motsvarande kontaktinteraktion mellan Alumec 89 och obelagd WC-Co hårdmetall visar däremot mer adhesiva tendenser. Dessutom tenderar temperaturutvecklingen i kontaktzonen under pinnsvarvning vara något lägre vid ytinteraktioner mellan CVD-diamant och Alumec 89. När det gäller materialöverföringsegenskaperna visar sig CVD-diamant fungera bra vid interaktion med höghållfast aluminium. Materialets vidhäftning minskar betydligt på diamantbelagda ytor. Vid kontinuerlig longitudinell svarvning med diamantbelagda skärverktyg observerades inget betydande slitage. Å andra sidan hittades tecken på både adhesivt och abrasivt slitage under svarvning med konventionella obelagda WC-Co hårdmetallverktyg. Slutligen visade det sig att de tribologiska mekanismerna som verkade under Tribojan-pinnsvarvning vara relativt jämförbara med faktisk bearbetning, vilket tyder på att testmetoden fungerar bra som komplement till friktions och svarvtester.

Machining of Aluminum can be complicated due to large amounts of adhesion and diffusion of the aluminum onto the cutting tool, causing effects such as built-up layers and built-up edges. This leads to poor surface finishes and can significantly affect the tool life. CVD diamond coated tools have shown to be a potential solution to this problem and is tested and analyzed as such in this thesis. CVD diamond coated inserts are tested and compared to uncoated cemented carbide inserts and Polycrystalline diamond tipped inserts, in milling, turning and in refined tribological methods. The workpiece material in both the machine tests and the tribological tests is a high strength aluminum of the name Alumec 89. The machine tests were performed for 5 and 60 seconds at three cutting speeds, 600, 900 and 1200 m/min, keeping other parameters constant. The cutting inserts, the chips and the generated workpiece surface are examined using LOM, SEM and EDS. In the refined tribological testing, a pin-turning tribometer is used, with pins of uncoated and coated (CVD diamond) cemented carbide pins. These are tested at 5 and 30 seconds at 600 and 1200 m/min, applying a constant force of 10 N. In addition, a friction test was performed to measure the friction of the uncoated and the CVD diamond coated cemented carbide. Like the cutting inserts, the used pins were examined in LOM and SEM. The results show that while a large amount of built-up layer and built-up edges gather when using uncoated cemented carbide tools, only minimal amounts can be detected on CVD diamond and PCD. It has also been shown that the reason for the reduced adhesion in the case of diamond tooling materials is most likely due to the lack of chemical interactions between the diamond and the aluminum. The friction of the CVD diamond material was shown to be lower compared to the cemented carbide. The surface finish generated by the different materials, was the best in the case of PCD while the CVD generated multiple small scratches that severely reduced the surface roughness. This thesis provides some initial basic understanding of the interaction of CVD diamond coated inserts with high strength aluminum alloys.

Fräsning och annan intermittent skärande bearbetning ger upphov till termisk utmattning av skärverktyg. Problemet med termiska sprickor blir större vid bearbetning av värmehållfasta material som austenitiskt rostfritt stål eftersom värmeväxlingarna i skärverktyget blir mer extrema. Detta fenomen förvärras ytterligare vid användning av traditionell kylning. Fräsning av rostfritt stål utförs därför torrt. Den torra bearbetningen är inte oproblematisk eftersom höga temperaturer uppstår i skärzonen vilket påverkar verktygets livslängd och i vilken utsträckning avverkningshastigheten kan höjas med högre skärhastighet eller matning. Detaljer som tar lång tid att tillverka är negativt för både företagens ekonomi och miljön till följd av större energiåtgång.Minimalsmörjning är en metod som går ut på att små mängder smörjmedel i form av aerosol fokuseras mot skäreggen och smörjer kontakten mellan arbetsstycke och skär, vilket minimerar friktionsvärmen. På detta sätt kan den totala värmeutvecklingen reduceras samtidigt som värmeväxlingarna hålls på en lägre nivå jämfört med traditionell kylning. Syftet med arbetet var att undersöka och jämföra planfräsning av austenitiskt rostfritt stål, 1.4301, under torr bearbetning och bearbetning med minimalsmörjning.Centralt för studien var hur verktygsförslitningen och ytjämnheten hos bearbetat material påverkas då minimalsmörjning appliceras gentemot vid torr bearbetning.En fråga som togs upp var om avverkningshastigheten kunde ökas med minimalsmörjning utan att få negativ inverkan på verktygsförslitning och ytjämnhet av bearbetat arbetsstycke.Fullfaktorförsök upprättades och jämförelsen mellan torr bearbetning ochminimalsmörjning gjordes med planfräsning med PVD-belagda hårdmetallskär. Ett optiskt mätmikroskop användes för att analysera förslitningen på skärverktygens spån- och släppningssidor efter ca 3 minuter i ingrepp. Ytjämnhet på bearbetad ytamättes med ytjämnhetsmätare och temperaturen i arbetsstycket mättes med termoelement.Resultatet visade att tillämpning av minimalsmörjning sänker temperaturen i skärzonen vilket för rostfritt stål innebär att skärhastigheten bör ökas för att undvika löseggsområdet. På så sätt ökar även avverkningshastigheten och produktiviteten. / Milling and other intermittent metal cutting operations often cause thermal fatigue in the cutting tools used. This type of wear is more severe during machining of heat resistant alloys such as austenitic stainless steel because of more extreme temperature variations during the cutting procedure. This phenomenon is further accelerated by employing flood cooling. Milling of stainless steel is therefore usually performed dry. Dry cutting is, however, not without its share of problems, since high temperatures develop in the cutting zone which adversely affect tool life and to which extent the productivity can be increased via higher cutting speeds or feed rates. Parts that take longer to manufacture are not only bad for business economics, but also for the environment due to higher energy consumption.Minimum quantity lubrication is a method that uses minimal quantities of oil dispersed as aerosol toward the cutting edge. This lubricates the tool-workpiece interface which minimizes frictional heat. This way, the total heat during cutting can be reduced while also avoiding the extreme temperature variations associated with flood cooling. The purpose of this thesis is to study and compare the performance of dry cutting and minimum quantity lubrication during face milling of austenitic stainless steel, 1.4301.The tool wear rates of the cutting tools and surface quality of the machined workpiece were compared for the two cutting environments. Of particular interest was the question whether the material removal rate could be increased with the usage of minimum quantity lubrication without adversely impacting the tool life or workpiece surface quality.A full factorial design of experiments was created, and the comparison of dry machining and minimum quantity lubrication was done by face milling with PVDcoated carbide inserts. An optical stereo microscope was used for the analysis of rake and flank wear after roughly 3 minutes of cutting tool engagement. Surface roughness of machined part was measured with a measuring stylus, and the temperature of the workpiece was measured with embedded thermocouples.The results show that minimum quantity lubrication reduces the temperature in the cutting zone, which for stainless steel means that the cutting speed should be increased to avoid the formation of built-up edges. At the same time, the material removal rate is increased, and productivity is affected positively.

Internal Combustion Engine (ICE) exhaust components are exposed to extreme operating temperatures. Thus, it is necessary that they are designed with materials that can sustain thermal and vibrational stresses. This study investigates the wear mechanisms and tribological performance of the exhaust manifold joint in Scania CV diesel trucks, focusing on the lip seal ring between the exhaust and turbo manifolds. The joint is prone to wear due to thermal and vibrational stresses, impacting its service life and raising environmental concerns. The manifold material, ductile cast iron SiMo51, offers good thermal resistance, while the lip seal ring, made of Inconel 718c, provides excellent thermal fatigue and corrosion resistance, coated with AlTiN for wear and oxidation resistance. However, the tribological performance of this joint and material combination remains unknown, necessitating further research.  This work aims to understand wear initiation mechanisms and their relationship with temperature. Test setups were established using an oscillating cylinder on disc configuration in the SRV 3 tribometer. SiMo51 uncoated/coated with Tribaloy 400 and Inconel 718c uncoated/coated with AlTiN were tested against each other to identify the best material pair. Analysis involved coefficient of friction, visual inspection, wear volume measurements, SEM micrographs, and EDS for surface chemical composition. Results indicated that friction behaviour is temperature-dependent, with oxide layer formation reducing the coefficient of friction when the manifold is uncoated, while the opposite occurs when coated with Tribaloy 400. Wear behaviour varied based on material combinations and temperature. Uncoated manifold exhibited dominant adhesion (galling) accompanied by tribo-oxidation at higher temperatures, with maximum wear volumes at room temperature. Introduction of T-400 on the manifold initiated galling on the lip seal, leading to abrasion on the manifold surface, accompanied by tribo-oxidation at elevated temperatures. Wear increased until 500°C, followed by a decrease at 700°C. Further explanations of T-400 wear behaviour are lacking in the literature.

The transition to a Circular Economy scheme that enables a more efficient usage of the resources is one of the most pressing needs in our society. From the industrial perspective this has been translated into new design philosophies and the search for more efficient systems. Polymeric composites have played a key role in the development of lighter components with good mechanical and tribological properties. Specifically, the demand of Carbon Fiber Reinforced Polymers (CFRP) has had an increasing trend since 1970s-1980s, becoming one of the kind of composites with the highest demand in the market to supply industries such as aerospace, automotive, construction, renewable energies, among others. With the increasing demand of CFRP materials some of the main challenges that arise are their disposal, environmental impact and cost of production to maintain the required supply. The use of Carbon Fibers as a reinforcement for polymeric matrices has been widely documented over the last decades, however the characterization of recycled Carbon Fibers for tribological applications is still scarce. Therefore, this investigation is focused on the mechanical and tribological characterization under water lubricated conditions of Ultra High Molecular Weight Polyethylene (UHMWPE) composites reinforced with virgin and recycled Carbon Fibers and Graphene Oxide. The findings of this work provide an important panorama regarding the performance of recycled Carbon Fibers, showing that they can have a comparable performance in mechanical properties and tribological behavior. This enables the use of recycled Carbon Fibers without compromising performance while reducing the environmental impact and cost.

The possible use of graphene and its derivatives dissolved in water as a green lubricant is an interesting avenue of research from tribological perspective. In this study, a highly concentrated stock solution of aqueous Graphene employing Polyethylene Glycol(PEG) as surfactant was diluted using proportionate volumes of De-Ionized (D.I.) water to generate target concentrations of Graphene in solution ranging from 15 μg/ml to 350 μg/ml . These samples were then tested for both sliding and rolling contacts. The sliding contact tests included the use of both 4-ball Tribometer test rig and triborheometer. The rolling contact tests were performed on Mini Traction Machine. The tested graphene-PEG-water admixtures held significant friction and wear advantage over D.I. Water and surfactant solutions under the same testing conditions. / Den möjliga användningen av grafen och dess derivat upplöst i vatten som ett grönt smörjmedel är en intressant forskningsaveny ur ett tribologiskt perspektiv. I denna studie späddes en högkoncentrerad grafenlösning med av-joniserat (D.I.) vatten för att alstra mållösningskoncentrationer av greven mellan 15 μg/ml och 350 μg/ml. Den testade grafenlösningen hade polyetylenglykol som ytaktivt ämne Proven testades sedan för både glidande och rullande kontakter. De glidande kontakttesten innefattade användandet av både en 4-kuletribometer och en triborometer. De rullande kontakttesterna utfördes med en Mini-traktionsmaskin. De testade proverna uppvisade signifikanta friktions- och förslitningsfördel jämfört med D.I. vatten och ytaktiva lösningar under samma testförhållanden

There has been much discussion about the beneficial uses of lamellar graphite iron in piston rings–cylinder liner systems, where a good combinations of both thermal and tribological properties are essential. The excellent tribological performance of lamellar iron under such sliding conditions is principally associated with lubrication behaviour of the graphite particles which are distributed as lamellas throughout the matrix. During sliding, graphite particles are extruded and smeared onto the counterfaces, act as solid lubricating agents and form a thin graphite film between the sliding surfaces. Although this process especially, during the running-in period significantly changes the sliding wear response of the components, the exact mechanism behind of this phenomenon has rarely been discussed in previous studies. It is tribologically beneficial to keep the graphite open, particularly in applications where the scuffing issues do matter. In this thesis, the main causes involved in closing the graphite lamellas are discussed, with a focus on matrix plastic deformation that occurs during sliding. In first step, the relationship between graphite lamellae orientation and plastic deformation was investigated. To do so, two piston rings, belonging to the same two-stroke marine engine operated for different periods of time, were selected and compared to the unworn sample. The worn piston rings displayed a substantial decrease in both frequency and area fraction of the graphite lamellas. Most of the lamellas were closed as a result of plastic deformation of matrix. This happening was caused mainly by the interaction between abrasive particles and metallic matrix. Additionally, it was found that graphite lamellas parallel or near-parallel to the sliding direction exhibited maximum closing tendency under sliding condition. In next step, to have a better understanding of the graphite film formation mechanism and matrix deformation role in closing the graphite lamellas, microindentation and microscratch testing were performed on typical lamellar iron. The qualitative results showed a similar mechanism involving in graphite contribution to lubricate the sliding surfaces. Moreover, microindentations made nearby the graphite lamellas demonstrated that the deformation of the matrix causes the formation of cracks in the centre of the graphite lamellas, compressing and then extruding the graphite from its natural position, irrespective of the lamellas′ size. Furthermore, it was found that subsurface graphite orientation had a large influence on the extrusion behaviour, in that, for graphite lamellas oriented towards the indenter, the effect was observed more pronounced. Furthermore, an improved fully ferritic solution strengthened compacted graphite iron was produced for future wear studies. The effects of different Si levels and section thicknesses on tensile properties and hardness were investigated as well. The influence of Si content and section thickness on mechanical properties was revealed by improving the materials strength and slightly enhancing the hardness through increasing Si content. Besides, Si addition up to 4.5 wt% significantly affected the strength and elongation to failure of cast samples. / Helios / FFI