Influence of microstructures on mechanical properties and tribology behaviors of TiN/Ti_xAl_1-xN multilayer coatings

There are demands to form nano-layered coating consisting of different materials in order to enhance the coating mechanical properties. However, poor structure control may lead to the formation of second phase and various defects. In this work, we endeavored to use cathodic arc deposition (CAD) method to fabricate TiN/Ti_xAl_1-xN nano-layered coatings with periods (Λ) ranging from 8 to 45 nm, which has great influences on coating microstructures and properties. X-ray diffraction (XRD), electron microscopy, nano-indentation and tribometry were employed to correlate coating microstructure and Λ with mechanical properties and wear resistance. The nano-layered coatings consisted of columnar grains with [111] texture, where individual grains contained low-angle grain boundaries without voids and amorphous phases. As Λ decreased, superlattices were generated, and reducing Λ from 45 nm to 13 nm yielded coatings with superior mechanical properties. The hardness peaked at 38.9 ± 3.6 GPa with a Young's modulus at 502.5 ± 40.4 GPa at 13 nm, however, when the Λ decreased to 8 nm the hardness and the Young's modulus deteriorated. It was concluded that wear resistance improved as the Λ decreased due to the greater interface population that impedes crack propagation. (authors)