Tribological performance evaluation of CrAlN-Ag and CrAlN/CrAlN-Ag coatings

Abstract

This study explores methods to enhance the performance of silicon nitride (Si₃N₄) bearings under oil-free lubrication by examining the tribological behavior of Ag-doped CrAlN coatings under varying loads. CrAlN-Ag and CrAlN/CrAlN-Ag coatings were deposited on Si₃N₄ substrates using radio frequency magnetron sputtering. The coatings were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while their mechanical properties were assessed through nanoindentation tests. Tribological performance was evaluated under different load conditions, and finite element analysis was employed to investigate the contact stress distribution within the coatings. The results reveal that Ag migrates toward the coating surface within a depth of approximately 250 nm, forming discrete Ag phases both internally and on the surface. Although Ag doping leads to a reduction in mechanical strength, the CrAlN/CrAlN-Ag coating demonstrates superior tribological performance under high loads. Furthermore, as the Ag concentration increases, the coating’s wear mechanism progressively transitions from abrasive wear to lubricated wear and, ultimately, to spalling wear.