Plastic flow behavior of (Cr, Al)N hard coatings in dependence of strain rate and nanostructure

Three coating systems, a nanolaminated CrN/AlN, a pure CrN and a pure AlN coating were deposited using High Power Pulsed Magnetron Sputtering. The coatings were analyzed using scanning electron microscopy and nanoindentation measurements with different strain rates. The indentation curves show a significant influence of the strain rate on coatings' strength. From the indentation data the yield stresses were determined using an analytical method and the flow curves were calculated using a finite element model of the indentation process. Both yield stress and flow curve show a strong dependency from strain rate and nanostructure. For high strain rates the pure coatings show an extensive increase in plastic strength which cannot be observed for the nanolaminated coating. The results are intensively discussed and suggestions to explain the different strain rate dependencies are made.