Tribo-electrochemical characterization of metallic biomaterials for total joint replacement

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.

Tribocorrosion behavior of beta titanium alloys in physiological solutions containing synovial components

Stefano Mischler

In this work, the tribocorrosion behavior of Ti-12.5Mo, Ti-13Nb-13Zr and Ti-29Nb-13Ta-4.6Zr beta titanium alloys which are candidate biomaterials for joint prostheses is studied against ultra high molecular weight polyethylene in Hank's balanced salt solution. Ti-6Al-4Fe alpha+beta titanium alloy is also tested for comparison. Experiments were carried out at open circuit potential and at a passive applied potential using a pin-on-flat reciprocating sliding tribo-electrochemical apparatus. The potential, anodic current and friction coefficient were measured in situ as a function of time. The beta alloys exhibited a tendency to repassivate during sliding at passive and open circuit potential. The predominant wear mechanism of the metal-polyethylene pairs was 3 body wear, exhibited by the transfer of polyethylene to all titanium alloys. Polyethylene showed a comparatively low wear against beta titanium alloys. The effect of the addition of synovial fluid constituents, namely bovine serum albumin, hyaluronic acid and dipalmitoyphosphatidylcholine on the tribocorrosion of Ti-29Nb-13Ta-4.6Zr alloy was also studied. The presence of additives affected the friction coefficient, induced an increase of the wear volume, and a modification of the dominant wear mechanism which was identified as abrasion without transfer of polyethylene. (C) 2010 Elsevier B.V. All rights reserved.

2011

Tribocorrosion of Pulsed Plasma-Nitrided CoCrMo Implant Alloy

Stefano Mischler

In the present study, a forged CoCrMo (ISO 5832-12) has been subjected to pulsed plasma treatment in a N-2/H-2 atmosphere at low temperatures (below 500 A degrees C). This treatment resulted in the formation of a layer composed by dispersed chromium nitride particles in a N-enriched metal matrix. The materials were tested for corrosion and tribocorrosion performance in 0.9 wt% NaCl at room temperature under controlled electrochemical conditions. After the treatment, the alloy loses its passive nature. The electrode potential was found to critically affect the corrosion and the tribocorrosion rates. In the nitrided alloy, a significant increase of corrosion rate was found at high potentials, while tribocorrosion was determined mainly by mechanical wear and not affected by potential. On the other hand, the untreated CoCrMo alloy exhibited stable corrosion over a wide range of potentials. Its tribocorrosion rate was similar to the nitrided alloy samples at low potentials, but it increased dramatically at high potentials where passivity triggered severe wear-accelerated corrosion and promoted mechanical wear. The present study shows that the electrochemical conditions determine material deterioration and should therefore be considered when selecting materials for tribocorrosion applications such as biomedical implants.

Springer Verlag2013

Chemical-mechanical polishing of tungsten

Jelena Stojadinovic

The chemical-mechanical polishing process (CMP) is an essential part of the production of integrated circuits. Metal to be polished in the CMP reacts with the oxidants from the aqueous suspension (slurry) and the passive film is formed on the metal surface. Suspended abrasive nano particles from the slurry cause detachment of the formed friable passive films. The CMP represents the tribocorrosion process where material deterioration results from the interaction of wear and corrosion which takes place in tribological contact exposed to an aggressive environment. Due to increasing number of the materials to be polished in the modern integrated circuits it is necessary to gather fundamental understanding of the removal mechanism of each material. The aim of this work is to elucidate the removal mechanisms of tungsten (W), as a typical microelectronic metal (chosen as a model system), under different oxidising conditions (represented by electrochemically imposed potential). Also, we want to evaluate the effect of the slurry composition (chelating agents lactic and phosphoric acid) on material removal. To achieve this electrochemical techniques (chrono amperometry, cyclic voltametry, passivation kinetics measurements under mass transport control), and tribocorrosion techniques (tests on tribometer with electrochemical cell with reciprocating sliding motion of alumina ball) were used. Surface analysis techniques (SEM, XPS, AES) were used to assess worn and unworn surfaces' morphology and chemistry. In addition, electrochemical tests and polishing tests on the CMP machine were performed with technical CMP slurries. The sliding action of the alumina ball on tungsten in the 0.01 M H2SO4 solution was found to cause three distinct wear responses depending on imposed electrode potential. Below the first threshold potential the wear is low due to negligible oxide film formation. In the following wear region, up to the second threshold potential, materials deterioration in the rubbed area proceeds by cyclic mechanical removal of the WO3 passive film followed by repassivation of tungsten. The amount of anodic oxidation corresponds to the overall removed metal volume. Beyond the second threshold potential a compact tribolayer of WO3 (more than 400 nm thick), probably formed by agglomeration of oxide particles detached from the metal surface, forms and covers the wear track. Similar tribocorrosion behavior of tungsten was also observed in the presence of 0.1 M H3PO4. The presence of chelating agents, lactic acid and phosphoric acid, in the 0.01 M H2SO4 solution does not change the volume of material wastage at potentials below the second threshold potential. Beyond this electrode potential, lactic acid promotes WO3 dissolution and thus impedes the third body formation and enhances wear. Electrochemical factors have a strong influence on the tungsten CMP removal rate. It was found that CMP removal rate increases with the open circuit potential (electrode potential) and with passivation charge density. A good correlation of tribocorrosion results and CMP practice was observed. Tribocorrosion models can be successfully applied to the tribocorrosion of tungsten and as well can be fairly used for modelling the material removal in CMP.

EPFL2009

Chemical-mechanical polishing of tungsten

Jelena Stojadinovic

EPFL2009