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Development of high performance tribological coatings for application onto hip joint prostheses
Knox, Paul
Knox, Paul
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2010
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Knox_PhD thesis.pdf
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In this thesis Graphit-iC™, an amorphous carbon coating developed by Teer Coatings Ltd. was modified and deposited onto CoCr and WHMWPE substrates in order to improve the wear properties. It was identified that depositing a hard coating onto soft substrate would cause high stresses and lead to coating delamination. Consequently the polyethylene substrates were ion implanted with nitrogen to reduce the hardness differential at the substrate-coating boundary. The coating was characterised using a pin on disc method in order to determine wear and friction. Hardness and fatigue was characterised using nano-indentation and the coating adhesion was measured using scratch testing. Application of the coatings resulted in a significant reduction in wear. Wear factors as low as 3.65x10¯18m³/Nm were achieved for coated CoCr substrates compared to 3.53x10¯15m³/Nm reported in the literature for uncoated CoCr. The coating resulted in friction coefficients between 0.12 and 0.19 with hardness ranging from 6.65 and 15.63GPa. Similarly coating UHMWPE resulted in a reduction in the wear factor to less than 9.6x10¯17m³/Nm. It was concluded that the deposition of amorphous carbon coatings can improve wear of hip joint prostheses, although consideration must be made for the adhesion of the coating to the substrate so that it does not contribute to an early failure of the device. Improved adhesion can be achieved by reducing the hardness differential between the coating and adhesion, either through softening the coating or by using interlayers.
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en
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A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the degree of Doctor of Philosophy
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EPSRC Case Studentship (Teer Coatings Ltd)