Cracking resistance and impact wear of thin and thick hard coatings under cyclic loading

Among wear resistant coatings and deposition techniques physical vapour deposition of hard thin coatings and high-velocity oxy-fuel spraying of thick WC-Co-based powder coating have provided good wear protection against various types of wear including impact wear. Three different substrate and coating systems-hard metal-coating, cold work tool steel-coating and nitrided steel-coating-were studied. Monoand multilayer coatings as well as duplex coatings were selected for testing. For characterization of coating systems nanohardness and microhardness as well as Rockwell adhesion test and single point indentation methods were used. Wear resistance of coatings was determined considering impact wear. The best adhesion determined by indentation was demonstrated by monolayer coating (TiN) on a hard metal substrate; the same coating system has a higher impact wear resistance. The coatings with multilayer structure (TiAlN) demonstrate better cracking resistance. Resistance to cracking as well as to impact wear depends on coating E/H ratio (at lower loads) as well as on substrate material E/H ratio (at higher loads). For characterization of resistance to plastic deformation for substrate H s3 =Es2 ratio was used. The obtained data enable a comparison of cracking and impact wear resistance of a coated system and selection of an optimal coating for metal forming tools applications. Copyright © 2012 by ASTM International.