Tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy in sulphuric and nitric acids: Electrochemical and chemical effects

Stefano Mischler
Elsevier, 2010
Article de conférence

The tribocorrosion behaviour of overlay welded Ni-Cr 625 alloy sliding against alumina in 0.5 M H2SO4 and 0.5 M HNO3 solutions under potentiostatic conditions was investigated. The passivation of the samples in the two electrolytes at different potentials ( -1.5, -0.3 and +0.3 V-MSE) was studied by means of potentiodynamic polarization curves and XPS. The tribocorrosion behaviour of the alloy in sulphuric acid was similar to the behaviour of stainless steels found in other studies, with much lower wear at cathodic potential compared to passive conditions. However, the behaviour in nitric acid was highly influenced by the reduction of nitric acid at the electrode-electrolyte interface. This reaction leads to the oxidation of the alloy even at cathodic potential. This feature influenced the tribocorrosion properties of the alloy in nitric acid, the wear rate at cathodic potential being in the same range as at passive potentials. (C) 2009 Elsevier Ltd. All rights reserved.

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Stefano Mischler
Elsevier, 2010
Article de conférence

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https://infoscience.epfl.ch/record/172614?ln=fr

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Applicability of a recently proposed tribocorrosion model to CoCr alloys with different carbides content

Marco Cantoni, Shoufan Cao, Stefano Mischler

Existing sliding tribocorrosion models have been developed for homogeneous passive metals such as stainless steel and pure metals. Many technical alloys contains however second phases, usually much harder than the metallic matrix, intended to provide better mechanical properties. The tribocorrosion models are based on the assumption of nearly perfect plastic behavior that is not necessarily representative of the tribological response of inhomogeneous metals. This work was initiated with the aim of evaluating the applicability to inhomogeneous alloys of a recently developed tribocorrosion model that includes mechanical, chemical and lubrication phenomena. For this the tribocorrosion of three different CoCr alloys was investigated using a reciprocating ball (alumina)-on-plate tribometer in a 0.5 M sulfuric acid solution. The alloys studied were a Stellite 6 (S6) with 22% of carbides, a Stellite 21 (S21) with 6% of carbides and a Stellite 21 (LCS21) without carbides. Tribocorrosion tests were carried out under potentiostatic conditions under different loads. Scanning electron microscopy, laser profilometry and focused ion beam were used for surface and sub-surface characterization of the wear tracks. The results obtained with the S21 and LCS21 alloys are consistent with the model while in the case of alloy S6, exhibiting interconnected carbide phases, the model correctly describes the corrosion response but only approximately the mechanical release of wear particles. (C) 2017 Elsevier B.V. All rights reserved.

Elsevier Science Sa2017

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Influence of Bovine Serum Albumin (BSA) on the Tribocorrosion Behaviour of a Low Carbon CoCrMo Alloy in Simulated Body Fluids

Shoufan Cao, Stefano Mischler, Choshun Yoneyama

Tribocorrosion, as the interaction between mechanical wear and electrochemical corrosion, has been found to be the main problem causing the failure and limiting the lifetime of metal-on-metal artificial hip joints. Better understanding of the tribocorrosion mechanisms of CoCrMo alloys is needed in order to reduce the degradation of this alloy, especially in the presence of proteins as one of the organic components present in synovial fluid. In this study, tribocorrosion tests of a low carbon CoCrMo alloy in phosphate buffer solution (PBS) with and without bovine serum albumin (BSA) in two different concentrations at different applied potentials (passive and cathodic) were carried out. The results show that the effect of proteins on wear and friction was concentration and potential dependent. In the cathodic domain (absence of very thin passive film), wear was very low in all solutions and the friction was significantly reduced by the addition of BSA to PBS even at low BSA concentrations. However, in the passive domain, the friction and wear were found not to be affected when the BSA concentration was 0.5 g/L, while they were reduced when increasing the BSA concentration to 36 g/L. The tribocorrosion results were rationalized through an existing tribocorrosion model and the effect of BSA on wear and friction was explained by the consideration of physical factors such as changes in viscosity and double layer structure, because in the present results no tribofilm formation was observed.

2020

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Fretting-corrosion behavior of beta titanium alloys in simulated synovial fluid

Stefano Mischler

Fretting-corrosion is a material degradation process resulting from the combined action of a corrosive environment and small displacement fretting wear. In this work, the fretting-corrosion behavior of Ti-12.5Mo, Ti-13Nb-13Zr, and Ti-29Nb-13Ta-4.6Zr, beta titanium alloys which are candidate biomaterials for joint prostheses was studied in Hank's balanced salt solution. Ti-6Al-4Fe alpha + beta titanium alloy was also tested for comparison. The open circuit potential, anodic current and friction coefficient were measured in situ, while the microstructure and volume of the wear track were characterized after testing. Ti-13Nb-13Zr and Ti-29Nb-13Ta-4.6Zr exhibited the ability to regain their passive state during fretting, while Ti-6Al-4Fe exhibited large dissolution pits around the wear track indicative of a widespread depassivation activated by fretting. The ability of these beta alloys to recover their passive state during fretting was related to the mechanical properties of the superficial passive layers and the evolution of the contact pressure defined by the wear of the alloy. The effects of the addition of synovial constituents, namely bovine serum albumin, hyaluronic acid and dipalmitoyphosphatidycholine on the fretting-corrosion of Ti-12.5Mo alloy were also studied. The addition of synovial constituents induced a decrease of the friction coefficient, the amount of elastic accommodation of the displacement and the wear rate of the alloy. (C) 2011 Elsevier B.V. All rights reserved.

2011

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