Self-lubricating nanoscaled metal matrix composites

Friction and wear are ubiquitous phenomena in mechanical components subjected to relative motion. The usual approach to reduce friction and wear has been for decades the use of fluid lubricants. The increasing complexity of mechanical systems and their progressively demanding operational environments require new engineering solutions for their proper functioning and extended duty life. For example, the application of fluid lubricants has been always severely restricted by the environmental conditions during operation, resulting mainly in their deployment in applications at, or near room temperature, so as to diminish their degradation. Furthermore, another challenge of fluid lubricants is the replenishment during operation, resulting sometimes in maintenance stops that affect the smooth operation.

An alternative to these drawbacks is the use of solid lubricants in self-lubricating systems, since it overcomes the most critical issues in a straightforward way. This approach, though already explored in the literature, still has a wide span of open questions that are critical for their extensive application. The first concerns the type of lubrication mechanism that is most suitable. Cur-rent solid lubricants present two main lubrication modes, being strictly different from each other. In layered lubricants, the mechanism is based on the interfacial shear and in fibre-like lubricants, the mechanism is a mix of rolling and gliding. The second open question is related to the integration of the lubricant to the containing technical metal. In this case, chemical and physical reactivity between both phases has to be explored for each particular system. Finally, the third main question lays on the possibility of finding an “all-rounder”, which might be able to operate in the most diverse and extreme conditions, without being significantly degraded and maintaining the required lubricity.

This project aims at providing a first integral and thorough analysis of self-lubricating compo-sites by combining an innovative manufacturing technology (high pressure torsion) and advanced microstructural and chemical characterization techniques. The chosen matrix materials are Ni-based superalloys, which find their application niche in extreme environments like, for example, turbine blades. As solid lubricants, traditional layered materials will be tested (graphite, MoS2 and WS2) and contrasted to novel solid lubricants (carbon nanotubes and graphene) that lack the usual operational limits observed in the former. After manufacturing, the composites will be extensively characterized before and after being subjected to sliding conditions in diverse environments (temperature and humidity). The main objective of the project is to obtain a self-lubricating composite that may function in a broad set of conditions.