Influence of copper on the compositions, microstructure and room and elevated temperature tribological properties of the molybdenum nitride film

Molybdenum nitride ceramic films, exhibiting excellent mechanical and frictional properties, have a great prospect for the application of high speed cutting tools and precision dies. However, the formation of lubricating tribofilm MoO3 with a layer structure always weakens the wear-resistance. In this paper, copper was added into the molybdenum nitride matrix using RF magnetron sputtering system to improve the tribological properties at room temperature (RT) and elevated temperatures. The results showed that face-centered cubic (fcc) Mo2N, fcc-Cu and CuO phases co-existed in the molybdenum nitride and copper films. As the Cu/(Cu + Mo) ratio increased, RT average friction coefficient (Cof.) dropped gradually due to the lubricating Cu and CuO phases, while wear rate (WR) initially decreased and then increased gradually after reaching a minimum value of similar to 1.2 x 10(-6) mm(3)/N.mm. WR at RT was mainly attributed by the soft lubricating phases, hardness and H/E ratio. The tribofilm changed from CuO to CuMoO4 and MoO3 as the testing temperature increased from 100 to 600 degrees C, this led to the drop in Cof. at the cost of WR.