The influence of Ag contents on the microstructure, mechanical and tribological properties of ZrN-Ag films

A series of ZrN-Ag films with various Ag contents (Ag/(Zr + Ag), at.%) were deposited by reactive magnetron sputtering and their microstructure, mechanical and tribological properties at various testing temperatures were investigated by the energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), nanoindenter and high temperature tribometer. The results showed that face-centered cubic (fcc) ZrN and fcc-Ag coexisted in the ZrN-Ag films. The hardness of the films, which was influenced by the fine-grain strengthening and the contents of soft Ag, initially increased gradually and reached a summit, then decreased with the increase of the Ag contents in the films and the maximum value was about 29 GPa at 0.3 at.% Ag. At room temperature, the average friction coefficient of the films first decreased and then almost remained stable with the increase of the Ag contents and the minimum value was 0.62 at 26.6 at.% Ag. The wear rate of the films first decreased slightly and reached a summit, then decreased with the increase of the Ag contents and the minimum value was 1.1 × 10−8mm3·N−1mm−1 at 0.3 at.% Ag. With the rise of the testing temperature from 200 °C to 600 °C, the combination of Ag into ZrN matrix could decrease the average friction coefficient of the films significantly and led to a relatively steady tendency of the average friction coefficient at the wide testing temperatures. However, the wear rate decreased with the increase of Ag content at the same temperature. Average friction coefficient and wear rate of the films regardless of the testing temperature were influenced by the soft lubricant Ag phase significantly.