The interface between TiAlN hard coatings and steel substrates generated by high energetic Cr+ bombardment

The microstructure of TiAlN coatings deposited by reactive unbalanced magnetron (UBM) sputtering after substrate bombardment with Cr ions, generated by a cathodic arc, and compositional changes of the ferritic steel substrate have been investigated for different bias voltages (Ub) during the Cr bombardment. Analysis was carried out using cross-sectional transmission electron microscopy (XTEM) and conversion electron Mössbauer spectroscopy (CEMS). The aim of the Cr bombardment is a substrate sputter cleaning effect. This is achieved when a bias voltage of −1200 V is applied. In this case subsequent UBM deposition of TiAlN leads to the growth of dense coatings exhibiting local epitaxy. For lower bias voltages CEMS indicates Cr deposition resulting in an open columnar structure of the subsequently grown TiAlN film, although small areas with oriented growth can still be observed.