Structure, mechanical properties and tribological behavior of Hf/HfN multilayer coatings deposited by magnetron sputtering

In this study, four different configurations of Hf/HfN multilayer coatings (bilayers) were synthesized by DC magnetron sputtering on AISI 304 steel. During the synthesis, the deposition time of Hf was kept constant for all coatings, while four variations in the deposition time of HfN were made, with a fixed total time. XRD analysis demonstrated the formation of one Hf phase and two HfN phases. Changes in the preferential orientation of HfN were observed with the increase in multilayers and the decrease of the HfN phase, as well as the presence of compressive stresses. Cross-sectional microstructural characterizations revealed a homogeneous structure of perfectly identifiable individual layers. The surface morphology exhibits a homogeneous distribution of small grains between 30 and 40 nm, with similar values to the crystallite size. These grains tend to group together to form clusters. The Hf/HfN multilayers exhibit hardnesses >33 GPa in the best condition obtained, as well as an improved COF of 0.29 and excellent wear resistance of 6.4 x 10(-4) mm(3)/Nm, with thicknesses ranging from 1.40 to 2.17 mu m. The hardness and COF performance are attributed to the multilayer structure that increases the H/E values, as well as the different phases and compressive residual stresses of HfN. The wear rate is related to the ceramic volume fraction, due to the wear mechanisms that occur in our tribological pair when interacting in the interlayers.