The direct contact of body and counter body can lead to atomic bonds (“micro weldings”), which are defined as adhesion [GAHR87, RABI95]. A relative movement of the contact partners does not necessarily involve that the bonds break within the original contact areas, so that material transfer can happen [HABI80].
Adhesive layers change the friction conditions. When steel components are ground with diamond wheels, built-up edges are formed on the diamond grits. They are mainly caused by the adhesion of steel particles on the diamond and not by welding processes of chips with the bonding [LINB70].
Focussed Ion Beam (FIB) separation allows damage free cutting of material samples out of the surface layer with electron transparency. Engelhorn [ENGE02, p. 90] found adhesive layers on sol-gel corundum grits after single grit scratch tests.
Supposedly, the nanocrystalline layer was molten and in a highly viscous state during grit engagement, so that friction and wear were reduced. Zeppenfeld [ZEPP05] found adhesive layers on diamond grits after scratch tests at y-titanium aluminide and identified the layers as workpiece material via Electron Beam Microanalysis (EBMA). Werner also discussed the wear minimizing effect of tribo-layers with cooling lubricant, but pointed out that the adhesive layers will wear also at some point [WERN73, p. 79].