Effect of volume fraction on mechanical properties of Zr/ZrN multilayer systems

In this paper we study the effect of volumetric fraction and bilayer modulation period (Λ) on mechanical properties of metal/ceramic multilayer coatings. Two sets of Zr/ZrN multilayer systems with different modulation period and volumetric fraction were synthesized by DC reactive magnetron sputtering. The crystalline structure of the multilayers films was determined by X-ray diffraction and morphology were analyzed by AFM and TEM, which show that crystalline films are formed in all cases. High resolution TEM analysis revealed well-formed multilayer composites with very smooth layers. Nanoindentation tests were carried out to measure the mechanical properties of the multilayer Zr/ZrN coating. Hardness (H), elastic modulus (E) and elastic recovery (We) were determined by using the Oliver and Pharr method, the values are also discussed in terms of H3/E2 ratio. The results show that mechanical properties varied according to volumetric fraction Zr/ZrN. However, coatings with metallic volume fraction between 10% and 20% showed a significant improvement in hardness of 16–21% in comparison with monolithic ZrN values. Moreover, the best values for elastic recovery and resistance to plastic deformation (H3/E2) also were found in Zr/ZrN multilayer with 10–20% of metallic phase, increasing up to 12% on We and up to 79% on H3/E2. These results allowed further understanding of the mechanical behavior of multilayer systems, demonstrating with this the importance of volumetric fraction in a metal/ceramic system.