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- Corrêa Filho, Luimar N., 1985-
(författare)
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Functional properties of silicon nitride based materials for joint applications
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Total hip and total knee replacements are generally successful procedures for patients suffering with pain due to bone fracture or diseases affecting the joints. However, the materials that are commonly used still have limitations. In particular, corrosion products and wear debris may give rise to negative body reactions.In this thesis, silicon nitride based materials were investigated for use in joint implants, namely as a coating for e.g. femoral heads and the metallic modular taper junction in hip implants, as well as a bulk bioceramic for joint applications. One of the main advantages of these materials is the potential to dissolve slowly in aqueous solutions, releasing only biocompatible ions.To understand the mechanical and wear properties of these materials, thin film coatings were deposited using magnetron-based techniques onto Si wafers and a CoCrMo alloy, the latter frequently used in biomedical implants. Coatings up to 8.8 µm thick were deposited on 2D flat discs as well as full 3D implant heads, following a CrN interlayer for improved adhesion. The chemical composition, microstructure, surface roughness, adhesion, wear resistance, and dissolution properties of the coatings were evaluated as a function of substrate rotation, bias voltage, target power as well as the addition of different elements.Results show that it is possible to produce coatings with mechanical properties and a wear performance similar to bulk ceramics and other ceramic coatings already evaluated in vivo. It was evident that a high coating density is needed, to avoid premature failure in an in vivo environment. The coating density, and stability over time in solution, was found to increase when a higher target power and process heating were used.New bulk silicon nitride materials containing only biocompatible additives, were evaluated for potential use in joint applications by wear tests for the first time, showing very low wear rates of the counter material.Silicon nitride coatings and bulk materials tested in this work showed promising results for further investigation and a basis for future application in joint bearings.
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| 2. |
- Skjöldebrand, Charlotte
(författare)
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Silicon nitride based coatings for biomedical implants
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon nitride-based coatings have been proposed as a means to reduce the release of metal ions and debris from metallic implants. This reduction in combination with the biocompatible debris from silicon nitride could result in a less adverse immune response. However, as the literature shows, introduction of coatings for biomedical implants is challenging and so far only a few alternatives have made it to market.This thesis focuses on the composition of silicon nitride-based coatings deposited using physical vapor deposition methods and its effect on material properties. Firstly, the effect of the nitrogen content was evaluated through the deposition of silicon nitride coatings using different nitrogen gas flow and substrate temperatures in a HiPIMS system. The highest nitrogen content was obtained by selecting a nitrogen-to-argon gas flow of 0.3 and substrate temperature of 350°C. This in turn resulted in the highest hardness, 25.9±2.1 GPa, which could prevent surface damage and this could in turn prevent wear.Further investigation aimed at improving adhesion, deposition rate and dissolution behaviour, and therefore investigated the effect of specific alloying elements (Fe, C, Cr and Nb) on hardness, elastic modulus, surface properties, dissolution and biocompatibility. In order to screen a range of compositions in an efficient manner the coatings used for this were either SiFeCN or SiCrNbN deposited with compositional gradients. The silicon nitride coatings with the incorporation of Fe and C (SiFeCN coatings) were found to reduce ion release from the underlying substrate and the coating itself when compared to pure silicon nitride coatings. While the SiFeCN coatings reduced the ion release from the underlying metal, the coating surface showed clear signs of dissolution after 14 days in simulated body fluid. The coatings alloyed with Cr and Nb showed a further reduction in ion release from the coating itself. The ion release correlated negatively with the Cr content in the coating, which could be due to the passivating properties of the surface oxide of these coatings.The work presented here shows the importance of the nitrogen content and its influence on the mechanical properties of silicon nitride coatings. In addition, the studies reveal a possibility to tune coating properties such as dissolution rate, while maintaining the biocompatibility, through alloying with elements Fe, C, Cr and Nb. In summary, this thesis has contributed to a further understanding of the influence of composition on the behaviour of silicon nitride coatings intended for biomedical applications.
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