Adhesion of coating has a great relationship with the surface condition of substrate and the coating adhesion is not very good in some surface. As a pretreatment method for vacuum coating, Sandblasting ensure good coating adhesion in some poor surface such as surface with oxide layer, etched surfaces, poorly ground or polished surfaces, etc.
The oxide layer and corrosion layer on the workpiece surface has very poor adhesive strength with substrates, these layers are easy to peel off with the action of temperature changes and stress, but they are difficult to completely clean out by washing.
During the heating process of the coating, some oxide layer and corrosion layer gradually peel off, but the rest are covered by the new coating. During the coating process, some oxide layer and corrosion layer also peel off with the action of stress. After the coating process, unpeeled oxide layer and corrosion layer are present between the substrate and the coating. During cooling process of the coating, these unpeeled layers would peel off with new coatings due to the thermal expansion and contraction stress. The rest new coatings attach to the substrates by oxide layer and corrosion layer, and the adhesion of it is poor, so these coatings will peel off first in the process of using the workpiece. And then the failure of the workpiece start and gradually spread and eventually leading to the failure of the entire workpiece. The peel off of the oxide layer and corrosion layer in the heating, coating and cooling process will affect the structural properties and the adhesion of the coatings, which eventually lead to the sharp decline of the coating’s service life.
Sandblasting can effectively remove the oxide layer and corrosion layer of workpiece before coating, so as to obtain the consistent surface quality to ensure good coating adhesion and reduce the discrete performance of coated tool in the process of using, which ensures stable cutting ability of tools. After sandblasting process, the workpiece surface is more delicate with uniform color.