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

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.

Mechanical and chemical mechanisms in the tribocorrosion of a Stellite type alloy

Marco Cantoni, Stefano Mischler

The tribocorrosion of a Stellite 21 type alloy sliding against alumina in sulfuric acid was investigated in order to identify relevant degradation mechanisms. Tribocorrosion tests were performed using a reciprocating motion pin-on-plate system operating under potentiostatic conditions as well as open circuit potential under different loadings. Scanning electron microscopy, optical microscopy, laser profilometry and focus ion beam (FIB) were used for characterizing wear pattern and subsurface deformation. Results show that the prevailing electrochemical conditions, and in particular the presence or not of a passive film, crucially affect the tribocorrosion behavior of this alloy. The passive film was found to significantly enhance tribocorrosion damage and this for two reasons: (i) abrasion of the passive film induces wear accelerated corrosion, (ii) the presence of the passive film significantly increases subsurface deformation in the metal and thus mechanical wear. The effect of electrode potential and normal load on the overall degradation by tribocorrosion could be accurately described by the Archard's wear law (taking into consideration the effect of the passive film) and existing models for wear accelerated corrosion.

Elsevier Science Sa2013

EBSD, SEM and FIB characterisation of subsurface deformation during tribocorrosion of stainless steel in sulphuric acid

Emmanuelle Boehm Courjault, Marco Cantoni, Stefano Mischler

The tribocorrosion behaviour of a 304L stainless steel/alumina contact was investigated in sulphuric acid at two imposed potentials (cathodic and passive) The metal deformation below the surface was investigated by analyzing cross sections using secondary electron microscopy (SEM) and electron back scatter diffraction (EBSD) Cross sections were also prepared using focussed ion beam (FIB) and analyzed by in situ SEM. AES depth profiling was used to analyze surface composition Metal subsurface deformation resulted in the build up of a deformed layer of approximately 20 mu m thickness in the near surface zone within the wear track This layer exhibited a deformation gradient with high deformation close to the surface resulting in grain refinement down to 10 nm The applied potential influenced the deformation at passive applied potential more strain was accumulated below the surface resulting in more pronounced grain refinement and higher density of defects. Using AES analysis no alumina transfer from the counter body or any significant burying of oxide below the surface could be detected (C) 2010 Elsevier B.V All rights reserved.

2010

Tribo-electrochemical characterization of metallic biomaterials for total joint replacement

Stefano Mischler

Knee and hip joint replacement implants involve a sliding contact between the femoral component and the tibial or acetabular component immersed in body fluids, thus making the metallic parts susceptible to tribocorrosion. Micro-motions occur at points of fixation leading to debris and ion release by fretting corrosion. beta-Titanium alloys are potential biomaterials for joint prostheses due to their biocompatibility and compatibility with the mechanical properties of bone. The biotribocorrosion behavior of Ti-29Nb-13Ta-4.6Zr was studied in Hank's balanced salt solution at open circuit potential and at an applied potential in the passive region. Reciprocating sliding tribocorrosion tests were carried out against technical grade ultra high molecular weight polyethylene, while fretting corrosion tests were carried out against alumina. The wear of the alloy is insignificant when sliding against polyethylene. However, depassivation does take place, but the tested alloy showed an ability to recover its passive state during sliding. The abrasivity of the alloy depends on the electrochemical conditions of the contact, while the wear of polyethylene proceeds through third body formation and material transfer. Under fretting corrosion conditions recovery of the passive state was also achieved. In a fretting contact wear of the alloy proceeds through plastic deformation of the bulk material and wear resistance depends on the electrochemical conditions. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Elsevier2012