Implications of the Presence of Y As a Reactive Element in Cathodic Vacuum ARC TiAlN Protective Coating for Tribological Applications

Abstract

The results of studies of the influence of Y as a reactive element on the properties of TiAlN coatings obtained by the method of vacuum-arc deposition are given. Changes in the structure and properties were analyzed using SEM in combination with EDX, XRD, indentation analysis and wear analysis. It is shown that the presence of Y changes the crystalline phase of the Ti0.6Al0.34Y0.06N coating. It consists of a combination of a cubic NaCl structure (basic phase) and a wurtzite structure (additional phase). In addition, it leads to a small grain size (12 nm) and a nano-columnar structure. The high hardness is partly the result of solution hardening due to the inclusion of larger Y atoms in the TiAlN lattice at the locations of the metal atoms. The reduced grain size of 12 nm also helps to increase the hardness of the coating. The hardness is 31 ± 2.5 GPa, the modulus of elasticity is 394.8 ± 35.8 GPa. The residual stress is approximately three times (−3352 ± 64 MPa) higher than the TiAlN coating (−720 MPa). In addition, a high level of compressive stress contributes to an increase in hardness, since defects responsible for their own compressive stress are an obstacle to dislocation movement. The improved hardness of the experimental coating can be explained by a triple effect: solution strengthening, grain grinding and high residual compressive stress. The addition of Y indicates a slower growth of the oxide layer on the surface of the coating during the wear test. After the addition of Y, Y ions preferentially separate at the grain boundaries and therefore effectively delay the inward diffusion of oxygen. The addition of Y promotes the formation of dense Al2O3, which is effective in restraining diffusion and therefore protects the coating from oxidative wear.

Keywords

• vacuum arc deposition
• coatings
• wurtzite phase
• hardness
• wear
• critical loads