SEM and AFM study of morphology and defects in PVD hard coatings
P. Panjan
Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
It is well known that the adhesion of hard coatings is not only dependent on deposition process parameters (substrate temperature, ion bombardment during growth), but also critically dependent on the tool material (composition, structure and morphology) and its pretreatment. All these deposition parameters and substrate properties have strong influences on the nucleation of hard coatings. Especially the carbides content and their size and distribution in the steel matrix has a strong influence on adhesion strength. The beneficial influence of teh MC carbides become pronounced still after sputter cleaning of the substrate. It is thus important to choose the substrate material, and its pretreatment very careful.
All samples (conventional and powder metallurgical high speed steels, high chromium type tool steel D2, cemented carbide) were ground, mirror-polished with 1 µm diamond paste and ultrasonically cleaned by a standard procedure in order to obtain optimum adhesion of PVD coating on a substrate. The termionic arc ion plating deposition system BAI 730 (Balzers) was used for preparation of TiN and CrN hard coatings, while the CemeCon CC800 deposition system equipt with four unbalanced magnetron sources was used for preparation TiN, CrN, TiAlN and CrN/TiAlN hard coatings.
The topography of uncoated and PVD-coated tool substrates was analysed by means of scanning electron microscope (SEM), atomic force microscope (AFM) and profilometer. SEM and AFM micrographs of the surface clearly show the carbide inclusions, which are especially clearly seen on PVD coated substrates, as a results of sputter cleaning (different carbides and the matrix have different sputtering yields). The influence of carbide inclusions in tool material on morphology of hard coatings will be presented.
Special attention is devoted to the surface defects. They can be results of insufficient cleaning procedure, as well as those, which appear due to deposition processes (droplets, particles incorporated during deposition). Attempts were made to find out the correlation between deposition parameters, surface pre-treatment, cleaning and type of substrate with the number and size of defects. Surface defects play an important role in corrosion protection of the coating/substrate systems.