Study The Structure And Mechanical Properties Of CrN Coatings Prepared By HIPIMS Technology

Chromium nitride(CrN) coatings, due to the high hardness with excellent toughness, high wear resistance and oxidation resistance etc., have been widely applied in the cutting tools, moulds, mechanical components of aerospace, MEMS fields. The main deposition methods of CrN coatings include arc ion plating (AIP) and common direct current magnetron sputtering (DCMS) currently. The arc ion plating technique owns the high ionization rate and growth speed of coating, while the co-depositoin of macroparticles during the deposition and the caused the rough surface and poor quality of coating is the key barrier to its potential applications. In another hand, the common DC magnetron sputtering technique benefits the coating deposition with smooth surface and large uniformity, but it suffers from the low ioinization rate (～1%) of targets and thereafter the poor adhesion strength and low hardness of coating. Recently, the High Power Impulse Magnetron Sputtering (HIPIMS) technology, combining the advantages of arc ion plating and magnetron sputtering, has drawn much attention due to the high ionization rate and co-deposition of macroparticle free. In this paper, we specifically investigated the CrN coating deposited by homemade HIPIMS systems. The effect of power discharge characteristic, deposition pressure, and substrate negative bias voltage on the structure and mechanical properties of CrN coatings were studied. The related results not only provide a basic understanding of the CrN coatings deposited by HIPIMS technique, but also offer a new guide to fabricate the hard coatings with high performance for the wear resistant applications.The results show that the pulse voltage and pressure play great role on the plasma charge charicteristics. With the increase of pulse voltage, the pulse current increases, which improves significantly the ionization rate of target material and benefits the coating deposition with high growth rate. While increasing the deposition pressure, the pulse voltage decreases. This is because the pressure is closely related to the mean free path of plasma particles. Generally the higher the pressure is, the shorter the free path of the particles is, which therefore strengthens the particles collision and leads to the kinertic energy loss. When the pressure inceases from4mtorr to8mtorr, the hardness of CrN coating decreases from18GPa to9.5GPa, and the surface roughness is deteriorated from5nm to23.7nm, respectively.Regardless of the changes in applied pulse voltage, the deposition rate of CrN coating is almost kept constant, and the coating is composed of single-phase CrN, which mainly includes the diffraction plane of (111).(200) and (220). However, noted that with the increase of pulse voltage, the diffraction peak broaden and the peak position shifts upward, which implies the size of lattice constant decreases with the view of micostructure grain refining. At the pulse voltage of700V, the coating exhibits the high hardness of18.5GPa and the lower roughness at4.65nm. as well as the excellent plastic deformation resistance.Increasing the negative bias voltage results in the micostructure refining of the CrN coating with columnar grains, and as a consequence of the observed high hardness. At the substrate bias of-50V, the grain size, the hardness and the elastic modulus of the coating is18nm,12GPa and228GPa, respectively. While in case of the bias at-250V, the grain size decreases to7nm, the hardness and elastic modulus increases to18.7GPa and286GPa, respectively. Further increasing the susbstrate bias leads to the slight decrease of hardness and the toughness of the depostited coating. At the bias of-250V, the coatings shows excellent plastic deformation resistance. the wear rate K.250v is lowest and it is about2.5×10-1mm3N-1m-1.