Microstructure and mechanical properties of TiN/CrN multilayer coatings deposited in an industrial-scale HiPIMS system

Abstract

TiN/CrN multilayer coatings of varying bilayer period (Ʌ) were deposited in an industrial-scale deposition plant by means of reactive high power impulse magnetron sputtering. By alternately sputtering titanium and chromium targets in a nitrogen-containing atmosphere, coatings with a Ʌ between 7 and 460 nm were obtained. The influence of Ʌ was investigated in regard of chemical composition, microstructure, and mechanical properties of the coatings. All coatings appear to be smooth and compact based on scanning electron microscope observations. X-ray diffraction showed separate crystalline phases of TiN and CrN for the samples with higher Ʌ. However, for the smallest periods (Ʌ7 and Ʌ15), the position of the peaks corresponding to the TiN and CrN phases overlap, which is consistent with the coherent growth of these phases and/or the formation of a ternary TiCrN crystalline phase. Additionally, the presence of satellite peaks points to a superlattice structure comprising TiN and CrN sublayers. High resolution transmission electron microscopy analysis on the superlattice samples evidenced an epitaxial growth across the superlattice interfaces for these coatings. An average compressive stress value of 2.2 GPa was measured, falling between those of TiN and CrN single-layer coatings. The sample exhibiting the highest hardness (H) and Young's modulus (E) values, reaching 31.9 GPa and 394 GPa, respectively, corresponded to Ʌ15. Nevertheless, while the Ʌ7 sample slightly reduced the H and E values (27.7 and 335 GPa respectively), it achieved maximum H/E and H3/E2 ratios, which are of particular interest to enhance wear resistance and prevent cracking failure. In summary, this work highlights the potential of depositing nanostructured multilayer coating with engineered interfaces and periodicities, providing exceptional mechanical and tribological properties, using a HiPIMS industrial deposition system.