Control Of Microstructure And Toughening Mechanics Of Cr-Me-N Coatings Deposited Using Magnetron Sputtering

This paper focus on the topic of toughness of CrN based hard coating. CrN based hard coatings with and without Al and Nb additions, including CrN/AIN, CrN/CrAl/NbN multilayers coatgings and CrAIN, CrAlNbN composite coatings, are prepared using closed unbalance magnetron sputtering ion plating system. Crack lengths from four corners of the Vickers indentations are measured, which are then used to estimate the coating fracture toughness (KIC). The crack resistance and toughness of various Cr-Me-N hard coatings with different preferential orientation and added with Al or Nb elements are discussed. Approaches to improve the toughness of hard coatings are introduced.Results show that deposited ratio of CrN coatings decreased with increase of bias voltage. Grain size of coatings slightly decreased with rising of bias, and has a minimum level of grain size of15.86nm at a bias voltage of-70V, then which increased with rising of bias. Lattice distortion (ε) of CrN coating slowly increased with rising of bias before-80V, which has a rapid increasing after-80V. The texture of CrN coating changed from a (200) preferential orientation to (111) with rising of bias voltage.Morphologies of CrN coatings after adding Al and Nb changed apparently. Tip of the crystalline column tends to be coarse and more defects can be found in the coating crystal. Addition of Al and Nb in CrN based coating can apparently hinder the coursing tendency of grains of coating. XRD results of CrN coatings added with Al and Nb are also showed in f.c.c. microstructure, that is to say Al and Nb elements might be dissolved in the matrix of CrN phase.Modulus of CrAIN coatings deposited using different sputtering current applied on targets does not changes clearly. But the coating with similar hardness showed quite different fracture toughness. That means hardness is not suitable for an individual evolution criterion to assess the crack resistance of a hard coating. Result shows crack resistance of a CrN based coating is closely associated with the fracture toughness. Fracture toughness of co-deposition coatings prepared at high sputtering current decrease apparently. Increasing of defects in coatings, much more coarse surface morphology and lower density might be the main reasons lead to drop in fracture toughness.The coating with optimum modulation period showed a best crack resistance for CrN/AIN multilayer coating. Change of concentration of Al and Nb in CrAlNbN coating has a clearly influence on the modulus of coating. But the mechanism is still not understood well. Fracture toughness of CrAlNbN coating improved with the rising of the percent of additives of Al and Nb, in contrast to the results for CrAlN coating.