Preparation and tribological properties of TiN-Cu gradient multilayer films on Si ₃ N ₄ ceramic substrates

To improve the friction and wear properties of TiN films on Si 3 N 4 ceramic bearings, a single-layer TiN film, a single-layer TiN-Cu film, and four groups of TiN-Cu gradient films with a gradient time T ranging from 30 to 90 min were deposited on Si 3 N 4 ceramics using magnetron sputtering technology. The microstructure of the films was investigated using an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and an X-ray energy dispersive spectrometer (EDS). The mechanical properties, friction, and wear properties of the films were tested using a nanoindenter, a scratch tester, and a friction and wear tester. The results indicate that under identical experimental conditions, TiN-Cu gradient films exhibit finer and more compact grains. The TiN grains in these films grow along the (111) direction, adopting a face-centered cubic structure. The overall performance of the TiN-Cu gradient film surpasses that of single-layer TiN and TiN-Cu films. At a gradient time of 50 min, the TiN-Cu gradient film achieves a maximum hardness of 27.6 GPa and an H 3 /E 2 value of 0.18 GPa. Its film-substrate adhesion is approximately 1.4 times greater than that of the single-layer film, reaching 34.7 N. The gradient film also demonstrates a significantly reduced friction coefficient and wear rate, with the lowest values recorded at 0.11 and 2.17 × 10 −6 mm 3 / (m·N), respectively, highlighting its superior friction and wear properties. Adjusting the gradient time during the preparation of the TiN-Cu gradient film effectively enhances its mechanical, friction, and wear properties, thereby broadening its application potential.