Effect of Powder Ball Milling Time on Microstructure and Properties of Mo₂NiB₂ Cermet

Molybdenum powder, nickel powder and boron powder were mixed by ball milling and press molded, and then Mo₂NiB₂ cermet was prepared by liquid phase sintering. The effects of powder ball milling time (1,12,24,36,48 h) on microstructure, hardness and electrochemical corrosion resistance of Mo₂NiB₂ cermet were studied. The results show that under different powder ball milling times, Mo₂NiB₂ cermets were all mainly composed of Mo₂NiB₂, MoB and MoNi phases. When the powder ball milling time was 24 h, the raw material powder was most evenly mixed, the content of the Mo₂NiB₂ phase generated by reaction was the highest, and the relative density of the cermet was the largest. With increasing powder ball milling time, the hardness of the cermet decreased first and increased and then decreased, and the free-corrosion current density increased first and decreased and then increased. When the powder ball milling time was 24 h, the hardness was the highest, and the free-corrosion current density was the smallest, indicating the corrosion resistance was the best. The best corrosion resistance was related to the reduction of diffusion channels of corrosive media due to the fewest pores in the cermet and the promotion of anodic polarization by the high content of Mo₂NiB₂ phase.