Tribocorrosion is an irreversible transformation of a material resulting from simultaneous physico-chemical and mechanical surface interactions in a tribological contact. Electrochemical methods are well suited for the study of tribocorrosion phenomena because they allow one to simulate the corrosive effect of the environment by imposing a fixed potential. Furthermore, the measurement of the anodic current permits one to determine the amount of material removed by oxidation as opposed to mechanical wear. In the present paper, experimental and theoretical aspects of applying electrochemical methods in tribology are discussed and recent results obtained with passivating metals in the authors' laboratory are presented. The importance of controlling the mechanical parameters and the contact geometry is stressed, and it is shown that these parameters can significantly affect the electrochemical response of a tribocorrosion system.

Electrochemical methods in tribocorrosion: a critical appraisal

Global energy consumption due to friction and wear in the mining industry

High wear rates and high patient ion levels have been associated with high (> 55°) cup inclination angles for metal-on-metal surface replacements. Wear rates and patterns have been simulated for ceramic-on-ceramic bearings by applying microseparation to replicate head offset deficiency. We tested 39-mm metal-on-metal surface replacements (n = 5) in a hip simulator with (A) an increased cup inclination angle of 60° and (B) an increased cup inclination angle and microseparation over 2 million cycles. (A) resulted in a ninefold increase in wear rate and (B) resulted in a 17-fold increase in wear rate compared to a standard gait condition study. Wear particles produced under microseparation conditions were larger than those produced under standard conditions but of similar shape (round to oval). The data suggest both head and cup position influence the wear of surface replacements; we believe it likely bearings with high wear either have a high cup inclination angle, an offset deficient head, or a combination of both.

High Cup Angle and Microseparation Increase the Wear of Hip Surface Replacements

Wear of CoCrMo alloys used in metal-on-metal hip joints: A tribocorrosion appraisal

Despite the satisfactory short-term implant survivorship of metal-on-metal hip resurfacing arthroplasty, periprosthetic soft-tissue masses such as pseudotumours are being increasingly reported Cytotoxic effects of cobalt or chromium have been suggested to play a role in its aetiology The aim of this study was to investigate the effects of clinically relevant metal nanoparticles and ions on the viability of macrophages in vitro A RAW 2647 murine macrophage cell line was cultured in the presence of either: (1) cobalt, chromium and titanium nanoparticles sized 30-35 nm; or (2) cobalt sulphate and chromium chloride Two methods were used to quantify cell viability: Alamar Blue assay and Live/Dead assay The cytotoxicity was observed only with cobalt Cobalt nanoparticles and ions demonstrated dose-dependent cytotoxic effects on macrophages in vitro: the cytotoxic concentrations of nanoparticles and ions were 1 x 10(12) particles ml(-1) and 1000 microM, respectively The high concentration of cobalt nanoparticles required for cytotoxicity of macrophages in vitro suggests that increased production of cobalt nanoparticles in vivo, due to excessive MoM implant wear, may lead to local adverse biological effects Therefore, cytotoxicity of high concentrations of metal nanoparticles phagocytosed by macrophages located in the periprosthetic tissues may be an important factor in pathogenesis of pseudotumours

https://iopscience.iop.org/article/10.1088/1748-6041/4/2/025018/pdf

Dose-dependent cytotoxicity of clinically relevant cobalt nanoparticles and ions on macrophages in vitro

To control and minimize wear of metal-on-metal hip joints it is essential to understand the mechanisms of debris generation. In vivo, mainly nanosize globular and needle-shaped particles are found. These can neither stem from the action of abrasion nor from tribochemical reactions. In this study the acting wear mechanisms have been first identified on the surface by means of scanning electron microscopy (SEM). Afterwards, the microstructures of the subsurface regions of explants have been investigated using a transmission electron microscope (TEM). Observation of the subsurface gave additional insight about the microstructural changes of cobalt-base alloys subjected to wear. At some distance from the surface, a network of stacking faults and hexagonal ϵ-martensite was found strengthening the bulk material. This microstructure changed into a nanocrystalline type moving closer towards the surface. A comparison of in vivo debris size and grain size of the surface suggests that the globular wear particles result from torn off nanocrystals, while the needle shaped particles are generated by fractured ϵ-martensite. Identified cracks, propagating through the nanocrystalline layer, further support these findings. Thus, it is suggested that the dominating mechanism of particle generation for metal-on-metal joints is surface fatigue within a nanocrystalline surface layer. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 72B: 206–214, 2005

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/jbm.b.30132

Subsurface microstructure of metal‐on‐metal hip joints and its relationship to wear particle generation

Microstructure of tribologically induced nanolayers produced at ultra-low wear rates

Metal-on-metal hip arthroplasties undergo distinct release of toxic metal particles and ions. Thus, it is necessary to minimize this. In order to evaluate the wear behaviour of metal-on-metal hip replacements it is essential to understand the micro-structural changes in the sub-surface region. Previous studies revealed that cobalt chromium metal-on-metal implants are able to alter their mechanical behaviour by adjusting the microstructure to load. The reason for this is the so-called mechanical mixing. This means that a nano-crystal layer is formed by rotating clusters of atoms that incorporate denatured proteins from the interfacial medium. This is followed by a layer of rhombic shaped nano-crystals in between sheared epsilon-martensite lathes, twins, and stacking faults. Although the primary wear zone has been well characterized, the sub-surface structure of the stripe wear and the non-contact zone of the hip ball have yet to be analysed. For this study a 28-mm cobalt base alloy femoral head and acetabular cup were analysed. The implant was simulator tested for 5 million cycles with the application of micro-separation resulting in a clearly visible stripe wear appearance. The TEM micrograph of the primary wear zone of the ball confirmed the presence of a sub-surface layer of nano-crystals. The thickness of this layer was approximately 200 nm and the average grain diameter ranged from 35 to 40 nm. Within the stripe wear zone the micrographs also revealed a nano-crystal layer but with a thickness of only 50 nm and an average grain diameter from 15 to 20 nm. The carbon and oxygen content was highest closest to the surface which proves the occurrence of mechanical mixing. The non-contact zone of the ball was analysed as well. When compared to the primary wear zone a nano-crystal layer with similar thickness but with an average grain diameter smaller than 15 nm was observed.

Subsurface changes of a MoM hip implant below different contact zones.

The effects of subsurface deformation on the sliding wear behaviour of a microtextured high-nitrogen steel surface

Any understanding of tribological behavior is connected to sound analyses of the wear appearances, which render insight into the acting wear mechanisms and their sub-mechanisms. Today one important method to analyze wear appearances at high resolution is transmission electron microscopy (TEM) being invented by Knoll and Ruska in the early 1930th in Berlin (Knoll in Z fuer Phys 78:318–339, 1932 [1]).

B. Gleising

Papers

Subsurface microstructure of metal‐on‐metal hip joints and its relationship to wear particle generation

Microstructure of tribologically induced nanolayers produced at ultra-low wear rates

Subsurface changes of a MoM hip implant below different contact zones.

The effects of subsurface deformation on the sliding wear behaviour of a microtextured high-nitrogen steel surface

Analyzing Mild- and Ultra-Mild Sliding Wear of Metallic Materials by Transmission Electron Microscopy