Ar + H2 plasma etching for improved adhesion of PVD coatings on steel substrates

Ar + H-2 plasma cleaning has been described for the surface modification of the steel substrates, which removes oxides and other contaminants from substrate surface effectively leading to a better adhesion of the physical vapor deposited (PVD) coatings. Approximately 1.1-1.3 mu m thick TiAlN coatings were deposited on plasma treated (Ar and Ar + H-2) and untreated mild steel (MS) substrates. A mechanism has been put forward to explain the effect of plasma treatment on the substrate surface based upon the data obtained from X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The XPS measurements on untreated and Ar + H-2 plasma etched MS substrates indicated that the untreated substrate surface mainly consisted of Fe3O4, whereas, after etching the concentration of oxides decreased considerably. The FESEM and the AFM results showed changes in the surface morphology and an increase in the substrate roughness as a result of Ar + H-2 plasma etching. Removal of oxide/contaminants, formation of coarser surface and increased substrate surface roughness as a result of Ar + H-2 plasma etching facilitate good mechanical interlocking at the substrate surface, leading to a better adhesion of the deposited PVD coatings. The adhesion of TiAlN coating could be increased further by incorporating a very thin Ti interlayer. (C) 2011 Elsevier Ltd. All rights reserved.