M.T. Mathew

Micro-abrasion transitions of metallic materials

Abstract Significant progress has been made in the understanding of micro-abrasion transitions of various materials in recent years, where abrasion is caused by particle sizes which are typically less than 10xa0μm. Research has shown reasonable consistency on effects of applied load and sliding distance, for studies carried out in various laboratories. In addition, attempts have been made to construct abrasion “diagrams” showing the transitions between the various regimes as a function of the above parameters. A puzzling aspect of the results to date, however, is the effect of “ridge” development on the micro-abrasion wear pattern. This ridge formation leads to a reduction in wear rate because the size of abrading particles, which account for the three-body effect, is less than the size of the ridge developed as a result of the wear process. The particles thus become lost in the ridge and cause no further abrasion. In this paper, the transition to ridge formation, as a function of sliding distance and load, is described for a range of pure metals of different hardness, using a TE-66, Plint micro-abrasion test rig. Tally-surf and optical microscopy techniques were used to measure the wear rate. Micro-abrasion maps were constructed showing differences in the transition boundaries between the wear regimes, and the implications of such results, for predictive modelling of micro-abrasion, are addressed in this paper.

Transitions in microabrasion mechanisms for WC-Co (HVOF) coated steel

Abstract In this work, the microabrasion of an HVOF (high-velocity oxy fuel) tungsten carbide (WC)-Co-based composite coating was investigated and compared with the performance of the substrate material, 316 stainless steel. The effects of sliding distance and applied load were investigated for both materials. Optical, scanning electron, and atomic force microscopy were used to characterize the surfaces following microabrasion. The results showed that the microabrasion rate peaked at intermediate loads for the materials. The critical load at which the peak was observed varied with sliding distance. There was a change in the performance of the coated versus the uncoated material, with the coating out-performing the substrate material at shorter sliding distances but with the reverse pattern occurring at longer sliding distances. The results were interpreted in terms of changes of microabrasion mechanisms as a function of increasing load and sliding distance. Microabrasion mechanisms were discussed based on the transition between wear volume as a function of load and sliding distance.

Special cluster issue on tribocorrosion of dental materials

Tribocorrosion affects all walks of life from oil and gas conversion to biomedical materials. Wear can interact with corrosion to enhance it or impede it; conversely, corrosion can enhance or impede wear. The understanding of the interactions between physical and chemical phenomena has been greatly assisted by electrochemical and microscopic techniques. In dentistry, it is well recognized that erosion due to dissolution (a term physicists use to denote wear) of enamel can result in tooth decay; however, the effects of the oral environment, i.e. pH levels, electrochemical potential and any interactions due to the forces involved in chewing are not well understood. This special cluster issue includes investigations on the fundamentals of wear–corrosion interactions involved in simulated oral environments, including candidate dental implant and veneer materials. The issue commences with a fundamental study of titanium implants and this is followed by an analysis of the behaviour of commonly used temporomandibular devices in a synovial fluid-like environment. The analysis of tribocorrosion mechanisms of Ti6Al4V biomedical alloys in artificial saliva with different pHs is addressed and is followed by a paper on fretting wear, on hydroxyapatite-titanium composites in simulated body fluid, supplemented with protein (bovine serum albumin). The effects of acid treatments on tooth enamel, and as a surface engineering technique for dental implants, are investigated in two further contributions. An analysis of the physiological parameters of intraoral wear is addressed; this is followed by a study of candidate dental materials in common beverages such as tea and coffee with varying acidity and viscosity and the use of wear maps to identify the safety zones for prediction of material degradation in such conditions. Hence, the special cluster issue consists of a range of tribocorrosion contributions involving many aspects of dental tribocorrosion, from analysis of physiological approaches and tissue engineering to studying of the effects of the environments encountered in clinical practice and management which lead to tooth decay. A wide range of analytical techniques and tribocorrosion experimental approaches is used to simulate, assess and model the synergistic interactions of wear and corrosion, many of them leading to new insights. We hope it will lead to increased awareness of tribocorrosion phenomena for researchers and dental clinicians alike and food for thought for further studies in this field.

Micro-Abrasion-Corrosion Mapping of Bio-Materials: Some New Perspectives

Recent developments in the studies of micro-abrasion have resulted in the construction of mechanistic maps where the change in micro-abrasion is presented as a function of the main tribological parameters. However, in many practical situations where micro-abrasion occurs, the environment tends to be corrosive. In such cases, the interaction of micro-abrasion and corrosion is of interest because the combined interaction may lead to “synergistic” or “antagonistic” effects, where corrosion may have a deleterious or beneficial effect in modifying the mechanical properties of the surface. In this paper, the micro-abrasion of a Co-Cr specimen against an ultra high molecular weight polyethylene (UHMWPE) ball was studied in Ringers solution. The effects of applied load at a range of electrochemical potentials were investigated. Atomic force and scanning electron microscopy techniques were used to identify the extent of wear and the role of the corrosion film on the micro-abrasion rate enabling the various wear, corrosion and the interactive effects to be evaluated for the system. The results showed that various micro-abrasion-corrosion mechanisms could be identified in active and passive conditions. These were used to generate micro-abrasion-corrosion mechanism maps showing the change in mechanism as functions of load and applied potential and the extent of interaction between the wear and the corrosion processes was demonstrated on such maps. Possible uses of the generic form of these maps to identify micro-abrasion-corrosion mechanisms in other bio-medical applications are addressed in this paper.Copyright