Abstract
Tribocorrosion covers the science of surface transformations resulting from the interaction of mechanical loading and chemical reactions that occur between elements of a tribosystem exposed to corrosive environments. Thus it combines the mechanical and chemical interactions of body, counterbody, interfacial medium, and environment including friction, lubrication, wear and tribologically activated chemical and electrochemical reactions. During friction the adhesive dissipation of energy is often influenced by chemical effects, while during wear the wear mechanisms of 'adhesion' as well as 'tribochemical reactions' are affected. The latter mechanism is of interest in mechanical engineering particularly, because it might prevent adhesion, which would bring about a much higher wear rate or even seizure. Nevertheless, in electronics as well as for MEMS and NEMS, chemical reactions are often avoided because they change the nature (e.g. conductivity, reactivity) of surfaces of sensors or alter the dimensions of parts within the nm- and μm-range by the growth of a reaction layer. Thus, depending on the structure and loading of the tribosystem, tribocorrosion phenomena could be either beneficial or detrimental.
In order to benefit from tribocorrosion phenomena it is crucial to control them as well as the nature of rubbed or worn surfaces, which have undergone tribological stresses. Unfortunately, the tribocorrosion mechanisms are still not well understood. Reasons for this stem not only from the complex interactions of chemical and mechanical factors but also from the experimental difficulty of characterizing mechanically and/or thermally induced surface phenomena occurring inside small contacts. Due to the fact that the duration of a single asperity contact is short and that it takes place directly at the interface of contacting bodies, even modern surface analysing techniques often fail. Many reactions could take place at the same time and the quantity of reaction products might be very small. In addition, metastable phases might be important inside a contact, which then transform into stable reaction products outside of the contact. Thus, in situ techniques are most suitable for tribocorrosion investigations. In the case of electronically conducting materials exposed to ionic conductive liquids, such as aqueous solutions, triboelectrochemical techniques offer interesting possibilities to control, in situ and in real time, the surface reactions occurring in a contact. However, further experimental developments are needed to obtain a clearer picture of the processes involved. Thus, tribocorrosion has been a point of basic research for more than 40 years and will remain as such in the near future.
This special cluster issue within Journal of Physics D: Applied Physics provides state-of-the-art information on tribocorrosion. Due to the fact that this research area is very large and complex, the given selection of papers will certainly not be representative of the entire field. The editors have tried, however, to offer a glimpse of what happens with metals, ceramics, and polymers when exposed to the combined action of friction and corrosion. Thus, this issue begins with a view on general and basic aspects of tribocorrosion. This is followed by papers which concentrate on the materials response to tribocorrosion and contributions related to 'abrasion' and 'surface fatigue' wear mechanisms. Finally the influence of tribocorrosion on certain applications is presented. This cluster should encourage natural as well as engineering scientists to carry out basic and applied research and should convince industrial chemists, physicists and mechanical engineers that there is hope.