Tribology concerns friction, wear and lubrication, a field in which TNO has been working closely with industrial partners for thirty years. We analyse the contact between materials at nanometre and metre scale, simulate it and take measurements using special advanced equipment. To ensure our knowledge remains up to date, we work in fundamental research projects with university groups.
We study all conceivable combinations of materials - steel, aluminium, polymers, ceramics - in contact situations in extreme conditions, in a vacuum at low temperature, for instance. We measure slide speeds up to 8 m/s, contact pressure to 8 GPa, temperatures to 800 ºC and other system parameters. We observe how the properties change through surface treatments such as vacuum evaporation, laser deposition, thermal injection, wet chemical and thermochemical deposition methods. In addition to these coatings we also study the influence of permanent lubrication (including MoS2) and plastics by varying their composition. We have a whole array of advanced measuring equipment for this analysis, some of which we have developed ourselves. Our vast experience allows us to quickly (automatically) measure, analyse and interpret.
We are building a set-up, the SEM vacuum tribometer, in which we can bring materials into contact with each other in an extremely high vacuum or controlled gas environment and measure the friction and wear. If the atmosphere contains no oxygen and/or humidity, unexpected things happen. Water films and oxide skins can cause damage through mechanical contact and thus expose a reactive surface. We first examine the physical process, damage to the surface, and later the chemical processes like adhesive wear. This is where two reactive surfaces that are chemically connected come into contact with each other and can shear through movement. The shearing can occur anywhere, not just at the interface, and this may cause small morsels of material to come on to the 'contra-surface'. Our measurement set-up can be employed in an electron microscope so that one can also see what one is measuring (wear track, particle generation). A piezo-electrical element in the measuring arm of a pin-on-disc configuration measures the friction force between two materials that slide across each other in this device that we developed and built ourselves.
A new method, confocal microscopy, allows us to very accurately measure, at sub-nanometre scale, the roughness of a surface. We have an advanced tool, a Sensofar PL¼2300, in which we can measure very smooth surfaces (like silicon slices) and very raw (worn) surfaces using two different techniques. Exact roughness measurements are important, for instance when adhesion is necessary. Roughness measurements are also used for contact-mechanics models. Contact can cause wear to occur and alter the surface, a process that we can monitor. A surface that is too smooth may stick for a while but can then become loose, known as the stick-slip effect, which leads to undesirable vibrations in the construction. The 3D pictures of the measurements provide a better view of the surface than the normal simple line scan. We would be happy to examine with you how we can best measure the properties of a surface, because while roughness is essential for some components, for others the measurements are equally vital.