Influence of protein adsorption on tribocorrosion behaviour of CoCrMo biomedical-grade alloys

CoCrMo alloys have been widely used in metal-on-metal hip replacements. They exhibit excellent long-term survival rates; however, recently, high failure rates associated with adverse local tissue reactions have been observed. CoCrMo alloys generally work extremely well; however, sometimes their wear rate is high. This work investigated protein adsorption effects on the tribocorrosion behaviour of CoCrMo biomedical-grade alloys under different surface and media conditions. The study of the wear mechanisms indicated that protein adsorption affects the corrosion and mechanical material loss of the investigated material. The synergistic and antagonistic behaviour of the material was correlated with the protein adsorption

Improved tribocorrosion resistance by addition of Sn to CrFeCoNi high entropy alloy

Among the high entropy or complex concentrated alloys (HEAs/CCAs), one type of system is commonly based on CoCrFeNi, which as an equiatomic quaternary alloy that forms a single phase FCC structure. In this work, the effect of Sn in an equiatomic quinary system with CoCrFeNi is shown to lead to a great improvement in hardness and resistance to tribocorrosion. The addition causes a phase transition from a single FCC phase in CoCrFeNi to dual phase in CoCrFeNiSn with an Ni-Sn intermetallic phase, and a CoCrFeNi FCC phase. The presence of both the hard intermetallic and this ductile phase helps to resist crack propagation, and consequent material removal during wear. In addition, the high polarization resistance of the passive film formed at the surface and the high corrosion potential of the Ni-Sn phase contribute to preventing chloride corrosion attack during corrosion testing. This film is tenacious enough for the effect to persist under tribocorrosion conditions

In-situ Ti-6Al-4V/TiC composites synthesized by reactive spark plasma sintering : processing, microstructure, and dry sliding wear behaviour

Titanium carbide (TiC) reinforced Titanium Matrix Composites (TMCs) have been synthesized via an in-situ reactive spark plasma sintering (SPS) process using commercial Ti-6Al-4V spherical powders pre-coated with 1 wt% carbon nanoparticles by low-energy ball milling. Graphite flakes are used as carbon source, which aids powder flow during mixing as lubricant. Graphite transforms to nano-crystallite carbon during mixing which is favourable for the rapid formation of TiC second phase in the following SPS process. The composites exhibited a novel honeycomb-like cellular microstructure with the formation of 5–6 vol% fine TiC submicron grains interconnected in the titanium α/β matrix. In addition, the reinforcement of the TiC phase with a nano-hardness of 12.4 GPa, improves the wear resistance of the parent alloy matrix (5.1 GPa), with a reduction of 26–28% in wear rate during dry reciprocating sliding tests against Si3N4 balls. During sliding, the wear debris (predominantly anatase TiO2) builds up on the raised TiC hard phase forming a barrier layer of adhered oxide that can protect the alloy matrix underneath from abrasion and oxidation, leading to a reduced wear rate

The influence of protein concentration, temperature and cathodic polarization on the surface status of CoCrMo biomedical grade alloys

CoCrMo alloys have been widely used in hip replacements. On the one hand they have exhibited excellent long-term survival rates, but recently high failure rates have been observed, associated with adverse local tissue reactions. It is still a puzzle why CoCrMo alloys sometimes work very well, while at the other times the failure rate is unacceptably high. The current work aims to investigate the influence of protein adsorption on the oxide layer properties and consequently on corrosion behaviour of CoCrMo biomedical grade alloys in different surface and media conditions. Electrochemical Impedance Spectroscopy (EIS), SEM and AFM were employed to characterise the surfaces. TEM was also used to reveal the subsurface chemical composition. The results showed a significant drop in the resistance of the oxide layer on the surfaces after some cathodic potential polarization. It was also shown that higher protein content and temperature reduced the oxide layer/metal surface interface resistivity. EDX quantitative chemical composition spot analysis of the subsurface after cathodic polarization showed a depletion of chromium in the outermost layer. AFM imaging and peak-force quantitative nanomechanical mapping QNM revealed lower adhesion forces for a relatively thick proteinaceous adsorbed layer on the surface after high cathodic polarization in particular at 50 °C

Effect of grain size and crystallographic structure on the corrosion and tribocorrosion behaviour of a CoCrMo biomedical grade alloy in simulated body fluid

CoCrMo alloys are used in hip and knee replacements due to their excellent long-term survival rates. However, high failure rates have recently been observed associated with adverse tissue reactions. CoCrMo alloy surfaces undergo microstructural changes during wear, including the formation of ε-martensite and, occasionally, a nanocrystalline surface layer. It is not clear whether these changes are beneficial or detrimental to the performance of the component. Thus, high-pressure torsion (HPT) was employed to produce different grain sizes and crystallographic structures in a CoCrMo alloy and the corrosion and tribocorrosion behaviour were critically investigated as a function of grain size. The results reveal a degradation of the corrosion resistance for the HTP processed samples. The contributions of mechanical and corrosion material loss in tribocorrosion is also examined

EIS data

The data is for CoCrMo alloys for biomedical applications. The data showed a significant drop in the resistance of the oxide layer after cathodic polarization. It was also shown that higher protein content and temperature reduce the oxide layer resistivit

EIS data

The data is for CoCrMo alloys for biomedical applications. The data showed a significant drop in the resistance of the oxide layer after cathodic polarization. It was also shown that higher protein content and temperature reduce the oxide layer resistivit