Microstructural and micro-mechanical investigation of cathodic arc evaporated ZrN/TiN multilayer coatings with varying bilayer thickness

• Published in: Surface & coatings technology 2022-02, Vol.432, p.128070, Article 128070
• Main Authors: Frank, Florian, Kainz, Christina, Tkadletz, Michael, Czettl, Christoph, Pohler, Markus, Schalk, Nina
• Format: Article
• Language: English
• Subjects: Arc deposition; Arc evaporation; Bilayers; Cathodic coating (process); Coatings; Columnar structure; Compressive properties; Cube texture; Fracture toughness; Grain growth; Hardness; Investigations; Mechanical properties; Microstructure; Monolayers; Multilayer; Multilayers; Nanoindentation; Residual stress; Thickness ratio; TiN; X-ray diffraction; Zirconium nitrides; ZrN
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2021.128070

Modifying the architecture of multilayer hard coatings allows to adjust the mechanical properties of these materials for a given application. Within this work, the effect of the bilayer thickness (Λ) and the individual sublayer thickness ratio on the microstructure and mechanical properties of ZrN/TiN multilayer coatings was investigated. Multilayer coatings with Λ of 570, 320 and 35 nm were deposited by cathodic arc evaporation and compared to TiN and ZrN single-layer coatings. The microstructure was investigated by X-ray diffraction (XRD) and scanning electron microscopy. All coatings exhibit a single phase face-centred cubic structure and a predominant (111) texture. A columnar structure was observed for all coatings and grain growth extending beyond the ZrN/TiN interfaces was evident in all multilayers. For all coatings, compressive residual stresses were determined by XRD using the sin2ψ method, where the multilayer sample with the largest Λ exhibited the highest compressive residual stress of −1.7 ± 0.2 GPa. Lower compressive residual stresses could be correlated with decreasing Λ and decreasing ZrN:TiN thickness ratio. Nanoindentation experiments as well as micro-mechanical bending tests were conducted to assess the mechanical properties of the coatings. The ZrN/TiN multilayer sample with Λ of 35 nm showed the highest hardness of 28.0 ± 1.1 GPa. This value is similar to the TiN single-layer and higher compared to the ZrN single-layer, which exhibited a hardness of 27.9 ± 1.4 GPa and 25.8 ± 1.3 GPa, respectively. While the ZrN single-layer showed the highest fracture toughness, the ZrN/TiN multilayer samples were identified as the mechanically stiffest and strongest of the investigated coatings, since they exhibited a higher fracture stress compared to the single-layer coatings. The obtained results allow to optimise the architecture of ZrN/TiN multilayer coatings yielding the desired coating properties for application in the cutting industry. •Arc evaporated ZrN/TiN multilayer coatings with varying bilayer thickness Λ•Smaller Λ leads to grain refinement and more pronounced (111) texture.•Multilayer coating with lowest Λ exhibits the highest hardness.•Highest fracture toughness for ZrN single-layer coating•Improved fracture stress for multilayers compared to single-layers