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Friction and Wear Mechanisms of Ceramic Surfaces, As Well As on Acquiring Knowledge About the Properties of the New Surfaces Created During Wear

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Friction and Wear Mechanisms of Ceramic Surfaces, As Well As on Acquiring Knowledge About the Properties of the New Surfaces Created During Wear Till Pappa, Mamma, Jens och Benny List of Papers I On the role of tribofilm formation on the alumina drive components of an ultrasonic motor J. Olofsson, F. Lindberg, S. Johansson, S. Jacobson, Wear, 267 (2009) 1295-1300 II The influence of grain size and surface treatment of the tribofilm formation on alumina components J. Olofsson, S. Jacobson, submitted to: Journal of American Ceramic Society III Influence from humidity on the alumina friction drive system of an ultrasonic motor J. Olofsson, S. Johansson, S. Jacobson, Tribology International, 42 (2009) 1467-1477 IV Tribofilm formation of lightly loaded self mated alumina contacts J. Olofsson, U. Bexell, S. Jacobson, submitted to Wear V On the influence from micro topography of PVD coatings on friction behaviour, material transfer and tribofilm formation J. Olofsson, J. Gerth, H. Nyberg, U. Wiklund, S. Jacobson, Wear 271 (2011) 2046-1057 VI Evaluation of silicon nitride as a wear resistant and resorbable alternative for total hip joint replacement J. Olofsson, T. M. Grehk, T. Berlind, C. Persson, S. Jacobson, H. Engqvist, submitted to: Journal of Biomaterials Research part B VII Fabrication and evaluation of SixNy coatings for total joint replacements J. Olofsson, M. Pettersson, N. Teuscher, A. Heilmann, K. Larsson, K. Grandfield, C. Persson, S. Jacobson, H. Engqvist, submitted to: Journal of Materials Science – Materials in Medicine Reprints were made with permission from the publishers. Author’s Contribution to the Publications Paper I Major part of planning, major part of experimental work excluding TEM analyses, major part of evaluation and writing. Paper II Major part of planning, experimental work, evaluation and writing. Paper III Major part of planning, experimental work, evaluation and writing. Paper IV Major part of planning, major part of experimental work excluding XPS and SIMS analyses, major part of evaluation and writing. Paper V Part of planning, part of experimental work excluding coating deposition and XPS analyses, part of evaluation and major part of writing. Paper VI Major part of planning, major part of experimental work excluding blood plasma incubations XPS, XRD, and ICP-MS analyses, major part of evaluation and writing. Paper VII Major part of planning, part of experimental work excluding DFT calculations, XRD and TEM analyses, major part of evaluation and writing. Parts of this thesis have been previously published (Papers I, III and V). These papers are reprinted with the kind permission from Elsevier. Contents Introduction.....................................................................................................9 Aim of the Thesis ................................................................................10 Overview of Tribofilms ................................................................................11 Friction and Wear of Ceramics .....................................................................13 Wear Mechanisms ...............................................................................13 Influence of Atmosphere .....................................................................14 Ceramics .......................................................................................................15 Ceramic Coatings ................................................................................16 Coatings ........................................................................................................17 PVD – Sputter Coating ........................................................................17 Coating Deposition ..............................................................................18 Friction Drive System of an Ultrasonic Motor .............................................20 Tribology in Hip Joint Replacements ...........................................................22 Hip Joint Replacements .......................................................................22 Biotribology.........................................................................................23 Tribological and Mechanical Testing ...........................................................25 Bench Testing ......................................................................................25 Ball-on-Disc Test.................................................................................26 Nanoindentaion....................................................................................27 Solubility Tests of Silicon Nitride .......................................................27 Surface Analysis ...........................................................................................28 Surface Characterisation......................................................................28 Chemical Surface Analysis..................................................................29 Tribofilm Formation, Friction and Wear of Alumina against Alumina........31 Tribofilm Formation on Alumina Surfaces .........................................31 Tribofilm Formation in Water and Different Humidity.......................37 Hardness of the Tribofilm....................................................................38 Chemical Composition of the Tribofilm..............................................39 Friction.................................................................................................40 Friction Behaviour and Tribofilm Formation of TaC/a-C Coating...............43 Friction, Wear and Solubility of Silicon Nitride for Total Hip Joint Replacements ................................................................................................46 Evaluation of Bulk Silicon Nitride ......................................................46 Evaluation of SixNy Coatings...............................................................49 Conclusions...................................................................................................53 Sammanfattning på svenska (Summary in Swedish)....................................55 Acknowledgements.......................................................................................58 References.....................................................................................................60 Introduction Friction, wear and lubrication have to be considered in most everyday situa- tions where physical movement is of importance. The science and technol- ogy of interacting surfaces in relative motion, which encompasses friction, wear and lubrication, is called Tribology [1]. This means that knowledge of tribology can also be applied for development of sports and sports equip- ment. For example, football shoes have studs which control the grip, i.e. the friction between the shoes and the grass. However, if it rains, water will act as a lubricant and the friction between the grass and the shoes decreases. If the grass has dried but not the soil, the soil under the grass is the most easily sheared material, and then the shearing takes place in the soil and yet another friction level will apply. In addition, the surface properties could change over time. Grass and soil could adhere to the shoes, smoothen the surfaces and thus change the friction behaviour. Further, it should be considered that the wear of the football field increases when the soil is softer. Contrastingly, if the field is hard and contains a lot of sand and stones, the studs will be worn and hence the friction decreases. In conclusion, in order to understand the friction and wear behaviour it is of high importance to consider the sur- face properties as they will develop over time due to the tribological contact. The initial surfaces will always change. Friction arises as a resistance to motion when a solid surface moves over another surface. The tangential friction force (FF) is proportional to the nor- mal load (FN) by the coefficient of friction (µ), therefore the friction equation can be expressed as: F µ F (1) FN This proportional law is called the First Law of Friction by Amonton 1699 [1]. The coefficient of friction depends on the materials in contact, and will change with time as the surfaces change. At each point of contact, the softest material will deform and the material with lowest shear strength ( ) will be sheared. However, when the surrounding conditions change, e.g. a lubricant is added (water on grass), the temperature changes (different shear strength of 9 the soil), and so on, the coefficient of friction will change. The friction is not only a parameter for the original materials in contact, it is a parameter for the whole, dynamic system! The materials in contact have to be well adapted to the system and therefore materials science is essential for tribology. In terms of football, different types of shoes and materials are used for different grounds to achieve the optimal friction between the ground and the shoe. The optimal friction is different for different systems. To reduce the en- ergy losses in machine elements, the friction should be low. A low friction is also desired in hip joints to facilitate body movement. However, the optimal friction is high in an ultrasonic motor’s friction drive system in order to transfer movement. Aim of the Thesis The aim of this thesis is to improve the function of ultrasonic motors, hip joint replacements and low-friction applications using ceramic materials and coatings. The investigations focus on understanding the friction and wear mechanisms of ceramic surfaces, as well as on acquiring knowledge about the properties of the new surfaces created
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