Study on the Preparation of Ultramicro Molybdenum Nitride Powder and Wear Properties of Its Coating

Using the specially designed mechanochemical ball-mill equipment, the ultramicro molybdenum nitride powders were prepared from pure molybdenum powders in ammonia atmosphere at room temperature by high-energy ball milling. The results show that the mass ratio of grinding media to powder was 4:1 and after milling for 30 h, the Mo2N of fcc structure was obtained, and the average particle size of powders was around 100 nm. It is found that the chemisorption of ammonia onto the fresh molybdenum surfaces created by milling was the predominant process during solid gas reaction, and the change of Mo electronic undersaturation induced by the grain refining also accelerated the bonding between Mo and N. The coating was formed on the 40Cr steel base using plasma spray method by mix Ni60 alloy powders and ultramicro Mo2N powders of 5wt%, 10wt% and 15wt%, respectively. Coating abrasion test under the condition of dry-grinding, 2h wear time and 300N test load showed that the wear-resisting property of coating added with ultramicro Mo2N powders could be improved greatly, and the wear-resisting property of coating increased with the increase of Mo2N content. In the abrasion process, the evenly distributed ultramicro Mo2N particles play the dispersion strengthening and self-lubricating role in the coating.