The Influence Of Plasma Nitriding On Microstructure And Properties Of CrN And CrNiN Coatings On Ti6Al4V By Magnetron Sputtering

With the rapid development of the aerospace industry,the applications of Ti6Al4V alloy are becoming more and more widely.The integration of plasma nitriding and magnetron sputtering can be used for the surface modification treatment of Ti6Al4V alloy,so as to improve its comprehensive performance.In this paper,the CrN and CrNiN coatings were deposited on the nitriding and non-nitriding surface of Ti6Al4V alloy by closed-field unbalanced magnetron sputter ion plating.The morphology,composition and phase structure of the coatings were characterized by SEM,EDS and XRD.Meanwhile,the hardness,elastic modulus and adhesion strength of the coatings were measured using nanoindenter and Rockwell hardness tester.In addition,the tribological resistance,high temperature oxidation resistance and corrosion resistance of the coatings were investigated by ball-on-disc tribometer,high temperature box type resistance furnace,and electrochemical workstation,respectively.The results indicate that CrN and CrNiN coatings deposited on the Ti6Al4V alloy both have a dense microsturucture without obvious defects,growing as a columnar crystal.In addition,the surface particle uniformity of the coatings declines obviously after nitriding.The CrN coating is mainly composed of a NaCl cubic lattice type CrN phase;after the addition of Ni,the diffraction peak of CrN(111)disappears instead of the appearance of Cr₂N phase.Moreover,the preferred growth orientation of the coatings changes from CrN(111)to CrN(200),and Niexists as the elemental form in the coating.The application of plasma nitriding significantly improves the hardness and elastic modulus of CrN and CrNiN coatings,which have much higher H³/E² values of 0.0821GPa and 0.0804GPa,respectively.Rockwell indenter test shows that the plasma nitriding can obviously improve the adhesion strength of coatings.Especially after the addition of Ni,there is no cracking area basically around the indentation.The friction and wear test and the electrochemical test show that the tribological and corrosion resistance of the coatings are both improved after plasma nitriding;the resistance of CrN coating is slightly better than that of CrNiN coating.The high temperature oxidation test shows that the high temperature oxidation resistance of the Ti6Al4V alloy is improved significantly after depositing CrN and CrNiN coatings.When the temperature is below 600?,the surface morphologies of coatings change little and there are no obvious oxide particles on the surface.However,when the temperature is up to 750?,the particles on the surface begin to melt and the XRD analysis shows that the coatings appear Cr₂O₃ phase.