Adhesion wear is based on an atomic bond at a microcontact surface between the active partners of the wear process through microwelding. This bond is very strong, which means that shearing through the relative movement of the active parts takes place at a different place than that of the original microcontact surface. Chemical adhesion is based on atomic interaction through thermally induced diffusion processes. In contrast, in mechanical adhesion, the surfaces of the active parts are engaged in the microrange, while high temperatures lead to surface deformation [Telle 1993].
|
|
|
|||
FIGURE 9.1 Types of grinding wheel wear.
9.2.2 Tribochemical Wheel Wear
In the case of tribochemical wear, chemical reactions take place either between the active partners of the wear process or with the surrounding environmental medium. These chemical reactions cause changes in the boundary layer properties, which lead to adhesion of reaction products on the abrasive grain and to grain damage. Factors of a tribochemical reaction are chemical affinity between the active partners and ambient conditions such as temperature, pressure, and concentration.
9.2.3 Surface Disruptions
Surface disruptions can be traced back to mechanical thermal alternating pressures opening up grain boundaries and cleavage planes. This leads to structure changes, fatigue, cracks, and separation of single particles causing breakage and cutting material failure [Zum Gahr 1987, Telle 1993].
9.2.4 Diffusion
Prerequisites of diffusion processes in the working zone are the adequate activation energy and a sufficient chemical potential of the active partners. The diffusion accounts for a thermal activation of single atoms, which, as a result, change places. This causes material loss, and impurity atoms are inserted into the grain surface, which might lead to a loss of hardness. Surface diffusion processes can be divided into intercrystalline diffusion along the grain boundaries and transcrystalline diffusion into the grain volume.