Stress and mechanical properties of Ti–Cr–N gradient coatings deposited by vacuum arc

Abstract

This paper reports on the investigation of Ti–Cr–N gradient coatings deposited by cathodic arc vapor deposition. The Ti–Cr–N coatings were formed by the method of condensation from a plasma phase in a vacuum with ion bombardment of sample surfaces with combined Ti and Cr plasma flows in a residual nitrogen atmosphere. Auger Electron Spectroscopy (AES) investigations showed that the deposited coatings exhibited compositional gradient: a Cr-rich transition layer was formed during pretreatment of the substrate with Cr ions and a main Ti–Cr–N layer of varying Ti and Cr composition along the coating thickness was obtained by changing the arc current of Ti and Cr cathodes during deposition. Transmission Electron Microscopy (TEM) observations showed that TixCr1−xN solid solutions, with 0.60<x<0.84 and 0.25<x<0.67 were formed, depending on the relative cathode current change. The grains size of coating was ∼ 10 nm.The biaxial stress, determined from X-ray Diffraction using the sin2ψ method, was compressive and varied from −2.2 to −2.7 GPa for gradient coatings grown on silicon and from −4.1 to −4.3 GPa for the samples grown on carbon steel substrates. Gradient coatings exhibited reduced internal stresses in comparison with coatings of constant composition (−3.9 and −5.6 GPa, for samples grown on Si and steel substrate, respectively). It is established that the mechanical properties (hardness and the modulus of elasticity) of gradient coatings are the superposition of the solid solutions TixCr1−xN of different concentration (0.60<x<0.84 and 0.25<x<0.67).