Mechanical Properties and Formation Mechanism of Surface Hard Nanocrystalline Carbon Diffusion Layer on 18Cr2Ni4WA Steel Induced by Supersonic Fine Particle Bombarding.

Nanostructured carbon diffusion layers were produced on the 18Cr2Ni4WA low carbon steel using supersonic fine particles bombarding (SFPB) with activated carbon powders and low-temperature annealing at 500 °C. The microstructures and the formation mechanism of hard nanocrystalline carbon diffusion layers were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and molecular dynamics simulation. Additionally, the nano-hardness of the diffusion layer was measured by nanoindentation apparatus and the tribological properties were tested by wear tester. The results show that the thickness of the hard nano-carburized layer is about 20 μm. During SFPB treatment, high-speed Al₂O₃ particles carrying activated carbon powder impact on the surface of 18Cr2Ni4WA steel, resulting in the formation of high-density dislocations and nano-surface structure, and a large amount of carbide precipitates at grain boundaries and internal defects. The carbon content of the steel surface increased from 0.17 to 4.2% (wt.%). After annealing treatment, the nano-hardness of the carburized layer reaches 7.6 GPa and the friction coefficient decreases to 0.63. [ABSTRACT FROM AUTHOR]