Since oil-in-water emulsions combine good cooling and lubricating capabilities, they have been commonly used in cold rolling nowadays. In order to understand the tribology characteristics of the emulsion during the cold rolling process, the effects of load, sliding speed, material of specimen, surface roughness and type of emulsion on the tribology characteristics of cold rolling are investigated by using the multi-purpose friction and wear tester.The P (load) ¡VV (sliding speed) curve was investigated under the conditions of load (below 2.4GPa), sliding speed (below 2.2m/s) at lower specimen roughness. Results show that QK-N36 emulsion can differentiate between boundary lubrication regime and initial seizure according to their friction coefficient, but RL-61 emulsion cannot differentiate them. Therefore, the load carrying capacity of RL-61 emulsion is better than that of QK-N36 emulsion, and its friction coefficient is also lower than that of QK-N36 emulsion. However, this tendency of experimental results is different from the cold-rolling practice.Under the lower load and higher surface roughness conditions with different hardness of specimen, the friction coefficient of RL-61 emulsion is higher than that of QK-N36 emulsion. This tendency of experimental results is the same as the rolling practice. Under the lower load condition with SDK-11 specimen, the friction coefficient of RL-61 emulsion varies gradually in the range of 0.07 ~ 0.09 located in the boundary lubrication regime, but the friction coefficient of QK-N36 emulsion reduces to 0.02~0.04 located in the mixed lubrication regime.

Basic physics teaches us that the frictional force (lateral force) needed to move objects on surfaces are proportional to load (normal force) – Amonton’s Laws. In tribology, this force is proportional to contact area, whereas Amonton is just a special case for contact area scaling with load. Such established laws do not seem to apply to small drops on flat, smooth surfaces in which frictional forces have an inverse relation to contact area and have time component prior to movement. Such phenomena can be explained by Shanahan-deGennes were intermolecular forces are considered for a deformed surface. Graphene is a special case where no time component is observed and frictional forces are attributed to its chemical homogeneity and stability. In the second part of this thesis, graphene is considered as nanofiller to build up polymer nanocomposites via Layer by Layer (LbL). Graphene Nanoribbons derived from multi-walled carbon nanotubes (MWCNT) offers a special case for thermoplastic polyurethane nanocomposites in that of thermally activated twisting morphology influences nanocomposite properties. Finally an electric field driven transdermal hydrogel drug delivery device has been demonstrated by just using CNTs, polyvinyl-borax gel and a CNT membrane

The no-slip boundary condition is the foundation of traditional lubrication theory. It says that fluid adjacent to a solid boundary has zero velocity relative to that solid surface. For most practical applications the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for special engineered surfaces the no-slip boundary condition is not applicable. Measured velocity profiles suggest that slip is occurring at the interface. In the present study, it is found that judicious application of slip to a bearings surface can lead to improved bearing performance. The focus of this thesis is to analyze the effect an engineered slip/no-slip surface could have on hydrodynamic bearing performance. A heterogeneous pattern is applied to the bearing surface in which slip occurs in certain regions and is absent in others. Analysis is performed numerically for both plane pad slider bearings and journal bearings. The performance parameters evaluated for the bearings are load carrying capacity, side leakage rate and friction force. Fluid slip is assumed to occur according to the Navier relation and the effect of a critical value for slip onset is considered.

Advancement in biotechnology has successfully converted the conventional bearing couples into artificial joints. Materials used today, however, have not been satisfactory. Problems such as osteolysis and aseptic loosening lead to failure of artificial joints and also the lifespan of these joints is to be further improved. This research targets two issues related to the problem: coatings and design of new generation biofluids. Superior to metals and polymers, ceramics are hard and biocompatible and exhibit low wear and friction. The ceramic-on-ceramic bearing pair could last for a long time which could be beneficial to younger and active patients who need a bearing pair which would last for more than 15 years to avoid the possibility of a revision surgery. The first part of this thesis deals with studying the microstructure-property relationship of new ceramic-based materials and coatings. Specifically, alumina (ceramic) coatings at different current intensities were tested in order to determine their feasibility as a biomaterial for artificial joints. In order to find a new avenue for developing biofluids, the second part of this thesis focuses on the failure of artificial joints under inadequate lubrication. Also due to osteoarthritis, synthetic biofluid is injected into joints to help relieve pain but it works for only 6-9 months. We propose a new method using noble gold nanoparticles to modify fluids. This was accomplished by mixing different concentration of nanoparticles with biofluid. This thesis consists of 6 sections. The first section is an introduction to tribology, biotribology and artificial joints which is followed by the second section which discusses the objectives of the research. The third section describes the materials and methods used in the research. The tribological characterization of MAO alumina coatings is discussed in the fourth section and the fifth section discusses the effect of nanoparticles on fluid lubrication. The last section is the conclusion.

The effect of using a boric acid based additive in lubricants and fuel enhancers was investigated in this study. Experiments were performed in a reciprocating and a continuous sliding ball-on-disk test equipment. Different oil types and temperatures were used. The aim of the experiments was to provide information about how these boron containing lubricants work in terms of chemistry and tribology. The surfaces after tribological contact were analyzed with Light Optical Microscopy (LOM), Vertical Scanning Interferometry (VSI), Scanning Electron Spectroscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). The boric acid based additive and the temperature used affected both the friction and wear. A higher oil temperature resulted in wider wear tracks. Oil with boron additive seemed to lower the friction coefficient at temperatures above 50 °C, compared to the same oil without boric acid; the reference oil. The tests also indicated that friction coefficients as low as 0.05 can be achieved by using a boron additive layer on the disk surface together with PAO-oil. Tribofilms containing Zn, P, S, Mg and O were formed in the wear tracks at high temperatures for both the reference oil and oil with boron additive. Oxidized regions were found in the tracks created from tests at 25 °C. Tests with oil containing boron additive resulted in lower Zn concentrations in the tracks, which is an indication that the boric acid based additive hinders the formation of these Zn rich tribofilms. To summarize, both oils and fuel enhancers with boric acid can obtain lower friction coefficients compared to those without this additive. The role of boric acid in the tests performed, both regarding the tribology and chemistry, is not yet fully understood and more chemical investigations are needed.

New nanomaterials and nanoparticles are currently under investigation as lubricants or lubricant additives due to their unusual properties compared to traditional materials. One of the objectives of this work is to investigate the tribological properties of these materials in relation to surface topography. Chemical etching and metal evaporation methods were employed to prepare surfaces with various topographies. Surfaces were sheared with the use of a nanotribometer and characterized with an atomic force and scanning electron microscopes. For a system consisting of ZnS nanowires dispersed in dodecane sheared across ductile surfaces, it was found that the geometry of the nanowire relative to the surface topography plays a significant role. Moreover, for brittle surfaces, it was found that beyond a certain roughness the frictional properties remain unchanged. In addition, this work is also intended to explore novel lubricants with nanoparticle additives in efforts to control friction and wear. A system consisting of silica nanoparticles dispersed in ionic liquids was examined at various concentrations. It was found that an optimum concentration of nanoparticles exists and yields the best tribological properties. Such work represents an important step in understanding the tribological properties of nanoparticle lubricant additives in general; one that may ultimately provide the guidelines necessary for designing novel, low-friction, and wear-controlling nanoparticle-based lubrication systems that minimize energy and material losses due to friction.

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The present thesis is a comparative study of the hydrodynamic effects of a few deterministic microasperity shapes in a thrust slider application. Numerical study based on finite difference methods is used to find the trend of important tribological properties such as friction and leakage. Also, this work utilizes a distinctive and practical approach for comparison by considering constant load conditions, instead of constant film thickness, as is expected in an operating thrust bearing. The results are encouraging and clearly reveal the existence of a transition point for asperity area fraction where a reversal in trends for both the coefficient of friction and leakage is observed. The shapes of asperities affect leakage but, have a negligible effect on coefficient of friction; however, the size and the type of asperity (positive or negative) do influence it. The effects of orientation, on the other hand, are found both on the coefficient of friction and leakage. Triangular asperities exhibit an advantage over the other shapes in terms of leakage. In general, the impact of shapes is distinguishable, more at higher asperity area fractions in accordance with the geometrical differences.

This thesis was written for a Swedish valve manufacturer to find out in what temperature regimes it was possible to replace electroplated hard chromium with autocatalytic electroless nickel-phosphorus. In this work the dry sliding wear properties of electroplated hard chromium and autocatalytic electroless nickel-phosphorus(10% P) were compared. All tests and investigations were done by using available equipment at Karlstads University. The tests were made to find out how the wear of these coatings behaved at different temperatures, how different substrates influence the wear of these coatings and how the roughness of the substrate surface influence the wear properties of these coatings. The method used for the wear tests was block-on-ring with a counterformal contact mode. The tests were executed in room temperature, 300C and 400C; with a normal load of 100N, sliding speed was 150rpm and duration of the tests were 15 minutes. All tests were done in an argon gas atmosphere. The coatings was deposited onto the cylinders with a thickness of 30µm. The different substrates used were an austenitic stainless steel(1.4404) and an austenitic-ferritic(duplex) stainless steel(1.4460). Half of the austenitic cylinders had a machined surface and all the others(including duplex cylinders) were machined and grinded to achieve a smoother surface. The blocks used as countersurface were made out of austenitic-ferritic(duplex) stainless steel(1.4460). Equipment used to investigate the wear tracks were stereo microscopy, profilometer, microhardness tester and scanning electron microscopy(SEM). The coatings were investigated in matter such as wear depth, wear mode, wear mechanism, chemical composition, topography, morphology, cross-section and hardness. The results of this work showed that the nickel coating wear tracks maximal depth were less deep than those of hard chrome, at room temperature. At elevated temperatures the performance varies. The coatings deposited onto cylinders made out of duplex stainless steel performed better than those deposited onto austenitic cylinders. The nickel coating performed better deposited onto the substrates with smooth surface and the chrome coating performed better deposited onto the substrates with rough surface