The new nanocapsule structure and cyclic tribological properties of Mo 2 N/Ag/Si 3 N 4 nanocomposite film

Nanostructured films present versatile properties in the area of friction. This paper introduced a adaptive nanostructured film with multiple cycle service capability. Based on the concept of capsule sustained-release, a series of Mo 2 N/Ag/Si 3 N 4 composite films with different Si contents were prepared. The results show that the films were mainly composed of fcc-Mo 2 N, fcc-Ag and Si 3 N 4, presenting a “capsule structure” with the encapsulation of Mo 2 N/Ag by Si 3 N 4. The crystalline Si 3 N 4 wrap the Mo 2 N to form a co-extended growth structure, when the Si content is lower than 6.3 at. %. However, the coherent interface could be destroyed for the film with higher content of Si (>6.3 at. %), owing to the transforming to an amorphous phase of Si 3 N 4. When annealed at 500 °C, the growth of Ag content on the surface is higher for film with 6.3 at. % Si than that of film with 11.4 at. % Si, indicating that the capsule structure with amorphous Si 3 N 4 can hinder the diffusion of Ag. With the increase of Si content, the hardness of the film increases firstly and then decreases gradually. The maximum hardness value of 34.3 GPa can be obtained for the film with 6.3 at. % Si. The average friction coefficient of Mo 2 N/Ag/Si 3 N 4 composite films with 6.3 and 11.4 at.% Si contents decreased from 0.48 to 0.33 and from 0.42 to 0.31 respectively with the increase of friction temperature from 200 °C to 700 °C under friction test. At the same temperature, the friction coefficient for film with 6.3 at.% Si is always lower than that of film with 11.4 at.% Si, but the wear rate is always slightly higher. The temperature-cycling friction times of nanocomposite films consisting of amorphous Si 3 N 4 capsule structure with11.4 at.% Si is twice that of crystalline Si 3 N 4 with 6.3 at % Si. The amorphous “capsule” structure can improve the multi-cycle serviceability of the film.