Micro-abrasion resistance of thermochemically treated steels in aqueous solutions: Mechanisms, maps, materials selection

The area of micro-abrasion is an interesting and relatively recent area in tribo-testing methodologies, where small particles of less than 10 μm are employed between interacting surfaces. It is topical for a number of reasons; its direct relation to the mechanisms of the wear process in bio-tribological applications, ease in conducting tests and the good repeatability of the test results. It has widespread applications in conditions used in the space and offshore industries to bio-engineering for artificial joints and implants.There have been many recent studies on the micro-abrasion performance of materials, ranging from work basic metals to nano-structured coatings. However, no significant work is reported on the micro-abrasion resistance of thermochemically treated steels. Hence, this paper looks at the performance of two thermochemically treated steels, Tenifer bath nitride stainless steel (T-SS) and vanadized carbon steel (V-CS) in such conditions with reference to the stainless steel (SS) by varying the applied load and sliding distance.The results indicated that T-SS demonstrates exceptionally poor resistance to micro-abrasion. It was observed that the heat treatment process and properties of the hardened layer (hardness and thickness) are extremely important in determining the micro-abrasion resistance of such steels. Finally, the results were used to develop micro-abrasion mechanism and wastage maps, which can be used to optimize the surface treated materials for micro-abrasion resistance.     

Determination of the wear resistance of traditional ceramic materials by means of micro-abrasion technique

Micro-abrasion techniques enable the surface wear of materials to be studied with greater precision than provided by other methods. In addition to their reliability, micro-abrasion techniques allow the wear phenomenon of the top-most layers to be studied while assuring, in the case of thin coatings, that this is not influenced by the substrate.In the present study, micro-abrasion technique (cratering with a steel ball) was used to determine the wear resistance of traditional ceramic materials, as a complementary test to the methodologies on a macroscopic scale that are customarily used for this type of material. In order to adapt the test to these materials, the individual effect of each test condition on wear resistance was isolated, while keeping the other conditions constant. The following variables were studied: diameter and angular velocity of the ball, abrasive suspension feed rate and grain size, sample–ball contact angle and groove in the supporting drive shaft. The values established were validated by performance of the test on materials of a glassy nature.The micro-abrasion test is shown to be a useful method for studying wear performance of ceramic glazes.     

Some views on the construction of bio-tribo-corrosion maps for Titanium alloys in Hank's solution: Particle concentration and applied loads effects

The micro-abrasion-corrosion behavior of a Ti alloy in Hank's solution was investigated using various electrochemical and microscopy techniques. The effects of applied load and particle concentration were assessed for various corrosion, wear and wear-corrosion components of the wastage. Electrochemical potentiodynamic and potentiostatic tests were carried out to assess the effects of tribological variables on the wastage rate. The results were used to generate micro-abrasion-corrosion mechanism, wastage and synergy maps. The potential application of such maps to optimize the materials for total replacement bio-implants is addressed in this paper.     

Micro-abrasion mechanisms of cast CoCrMo in simulated body fluids

The abrasion seen on some of the retrieved CoCrMo hip joints has been reported to be caused by entrained hard particles in vivo. However, little work has been reported on the abrasion mechanisms of CoCrMo alloy in simulated body environments. Therefore, this study covers the mapping of micro-abrasion wear mechanisms of cast CoCrMo induced by third body hard particles under a wide range of abrasive test conditions. This study has a specific focus on covering the possible in vivo wear modes seen on metal-on-metal (MoM) surfaces. Nano-indentation and nano-scratch tests were also employed to further investigate the secondary wear mechanisms—nano-scale material deformation that involved in micro-abrasion processes. This work addresses the potential detrimental effects of third body hard particles in vivo such as increased wear rates (debris generation) and corrosion (metal-ion release). The abrasive wear mechanisms of cast CoCrMo have been investigated under various wear-corrosion conditions employing two abrasives, SiC (4 μm) and Al₂O₃ (1 μm), in two test solutions, 0.9% NaCl and 25% bovine serum. The specific wear rates, wear mechanisms and transitions between mechanisms are discussed in terms of the abrasive size, volume fraction and the test solutions deployed. The work shows that at high abrasive volume fractions, the presence of protein enhanced the wear loss due to the enhanced particle entrainment, whereas at much lower abrasive volume fractions, protein reduced the wear loss by acting as a boundary lubricant or rolling elements which reduced the abrasivity (load per particle) of the abrasive particles. The abrasive wear rate and wear mechanisms of the CoCrMo are dependent on the nature of the third body abrasives, their entrainment into the contact and the presence of the proteins.     

On the construction of micro-abrasion maps for a steel/polymer couple in corrosive environments

There has been significant recent interest in the interactions of micro-abrasion in aqueous conditions, particularly when the environment is corrosive. This is due to the fact that there are many micro-scale-abrasion processes where the presence of the corrosive media may modify the wear on the surface. Furthermore, if the surface dissolves, the mechanical properties of the surface may be modified as a result of the effects of corrosion.In this work, the micro-abrasion of a steel/polymer couple was studied in carbonate/bicarbonate solution. The effects of two variables, applied load and potential, were investigated on the wear rate enabling quantification of the corrosion and wear contributions. Scanning Electron and Atomic Force Microscopy were used to characterize the surfaces following micro-abrasion-corrosion.The results indicated possible micro-abrasion-corrosion mechanisms on the surface. These regimes were suggested on the basis of the ratio of the micro-abrasion to the corrosion rate. In addition, micro-abrasion-corrosion maps were constructed showing the transitions between the micro-abrasion-corrosion regimes as a function of load and applied potential.