The effect of applied load on tribological behaviour of PVD-CrN coatings

Specimens in tool steel for mould applications were characterized in the as- received condition (HB hardness =395) and after the coating deposition step characterize by a double layer of CrN obtained through Sputtering or Cathodic Arc technique. All the coated samples were 4 micron thick. The coating characterization was done by scratch testing, nanohardness measurements and Calotest data. The wear behavior was systematically studied through dry-sliding wear tests carried out both at room temperature and in temperature up to 533 K using a pin- on- disk configuration. Different normal applied loads were considered in the range of 1N to 10N. During each tribological testing the friction coefficient was evaluated and at the end of each test the worm surfaces were investigated using a Scanning Electron Microscope (SEM) and the damage mechanisms were also interpreted in terms of level of applied load vs. local plasticity of the steel substrate and imposed temperature. The influence of the deposition technique on the microstructural, mechanical and tribological properties was also pointed out and a particular attention was devoted to the coating defects (droplets) or discontinuities (interfaces) during the discussion of the phenomena such as delamination or reduction of the critical load