Fretting corrosion at the taper interface of modular hip implants has been implicated as a possible cause of implant failure. This study was set up to gain more insight in the taper mechanics that lead to fretting corrosion. The objectives of this study therefore were (1) to select experimental loading conditions to reproduce clinically relevant fretting corrosion features observed in retrieved components, (2) to develop a finite element model consistent with the fretting experiments and (3) to apply more complicated loading conditions of activities of daily living to the finite element model to study the taper mechanics. The experiments showed similar wear patterns on the taper surface as observed in retrievals. The finite element wear score based on Archard’s law did not correlate well with the amount of material loss measured in the experiments. However, similar patterns were observed between the simulated micromotions and the experimental wear measurements. Although the finite element model could not be validated, the loading conditions based on activities of daily living demonstrate the importance of assembly load on the wear potential. These findings suggest that finite element models that do not incorporate geometry updates to account for wear loss may not be appropriate to predict wear volumes of taper connections.

Defect growth in multilayer chromium nitride/niobium nitride coatings produced by combined high power impulse magnetron sputtering and unbalance magnetron sputtering technique. Thin Solid Films, 636, 558-566.

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Substrate bias voltage is one of the most influential deposition parameter for physical vapour deposition processes as it can directly control the adatom mobility during coating growth. It influences the hardness, roughness as well as the microstructure of the coatings. Thus, bias voltage could also affect the defect formation during the coating deposition. High Power Impulse Magnetron Sputtering (HIPIMS) has been proven useful in producing void free and arc droplet free dense coatings. However, such coatings can still suffer from some defects associated with external factors (independent of deposition technique), such as substrate irregularities and the flakes coming from the chamber components. In order to study the effects of bias voltage (U b) on the defect formation during HIPIMS process, four sets of CrN/NbN coatings were deposited at U b =-40 V,-65 V,-100 V and-150 V. Microscopic studies revealed that with the increase in bias voltage the coatings morphology was altered and the percentage of surface area covered by optically visible defects was increased from 3.13 % to 4.30 %. The defects on the coatings deposited at U b =-100 V and-150 V led to preferential corrosive attack resulting in a sharp increase in corrosion current density during Potentiodynamic polarisation experiments. Room temperature pin-on-disc tribological tests exhibited the influence of defects on the wear behaviour; however, the coefficient of friction (µ) values were mainly influenced by the nature of the oxides formed during the tests. Coating microstructure and bilayer thickness, along with the coating defects determined the coefficient of wear (Kc) values. This study revealed that the coating deposited at U b =-65 V had the highest wear resistance (Kc = 2.68 × 10-15 m 3 N-1 m-1) and the lowest friction (µ = 0.48).

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