Understanding the influence of post-annealing duration on the tribological and electrochemical performance of CrN/CrAlN Nano-multilayer coatings

This study investigates the effect of post-annealing time on the structural, mechanical, tribological, and electrochemical performance of CrN/CrAlN multilayer coatings deposited on AISI 4140 steel via cathodic arc evaporation (CAE). The coatings were subjected to annealing at 500 °C for durations ranging from 60 to 180 minutes. Comprehensive characterization techniques, including X-ray diffraction (XRD), nanoindentation, FE-SEM, Rockwell-C adhesion testing, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP), were employed to evaluate the time-dependent evolution of coating properties.XRD tests indicated a gradual transformation from CrN to Cr 2 N phases and oxidation layer formation, Cr 2 O 3 , with the increase of annealing time. The crystallite size of the films increased from 25nm to 40nm, and that of residual compressive stress decreased from -398 MPa to -297 MPa. Mechanical testing indicated decreased values for H from about 24 GPa (as-deposited) to 12 GPa (180 min), reduced the H/E and H 3 /E 2 ratios, suggesting less elastic recovery, and reduced wear resistance. 3.3 times higher wear rate in 180 min was obtained from tribological testing. According to electrochemical analysis, the 120 min time point showed the highest corrosion resistance with a decrease from 6.13 to 2.36 μA·cm -2 and an increase in polarization resistance from 17 kΩ·cm 2 to 23 kΩ·cm 2 . These results indicate that an intermediate annealing time (120min) is the most suitable to equilibrate the stress relief, phase stability, and passive layer. The findings represent important information for engineering CrN/CrAlN multilayer coatings, which can find application in wear- and corrosion-resistant solutions intended for automotive, tooling, and marine industry.