Effect of Vacuum Hot Pressing on Plasma-Sprayed Molybdenum Coatings on Rail Vehicle Axle Steel

摘要

Railway axles suffer severe friction damage during service. In this work, a pure molybdenum coating was prepared on EA4T axle steel by air plasma spraying and hot pressing to improve the steel lifetime. The phase composition, microstructure, hardness, and tribological properties of the coatings were characterized. The results showed that the Mo coating had typical lamellar structure with low porosity and oxidation. Hot pressing compacted the coating and improved the microstructure uniformity. The hardness of the Mo coating and its bonding strength with the substrate were increased after hot pressing under 60MPa at temperatures ranging between 400 and 500 degrees C, due to reduced porosity and enhanced mechanical bonding between the coating and substrate. In addition, both the friction coefficient and wear loss of the Mo coating were lower than those of the EA4T steel, illustrating its lubricating effect. Observation of worn surfaces showed that the delamination wear of the Mo coating could be relieved after proper hot pressing due to the strengthened bonding between lamellae.