In this work, the dynamic behavior of nano-bubbles near the surface of single crystal iron (Fe) was investigated using molecular dynamics simulations. The cavitation erosion behavior of single crystal Fe and the structural evolution of its eroded surface was examined at different bubble diameters. The results show that nano-bubble diameter is inversely correlated with impact pressure and diameter is positively correlated with nanojet energy. The volume, surface area, and depth of cavitation pits are nearly directly proportional to the bubble diameter with correlation linear fitting coefficients of R2 = 0.9837, R2 = 0.9922, and R2 = 0.9799, respectively. Additionally, cavitation erosion induces the structural evolution of iron atoms from bcc to fcc and hcp structures. The percentage of new phase transformed is related to the bubble diameter and the type of transformed structure, the percentage of fcc and hcp structures of Fe atoms exhibits an increasing trend with the increase in the bubble diameter, and the Fe atoms of fcc structures occur an obvious increase beyond a bubble diameter of 12 nm.

The surface of AISI 52100 steel was pre-treated by laser remelting with different powers, and the vanadizing layer were prepared on remelted steel by pack cementation. The microstructure and properties of vanadizing layer were investigated by XRD, microhardness tester, metallographic microscope, scanning electron microscope, energy dispersive spectrometer, friction and wear tester. The critical load L_c was determined by observing the micro-scratch morphology of scratches through micro-scratch experiments, and its wear performance was studied. The results show that the hardness of remelting zone increase with the increase of laser power. When the laser power is 500 W, the microhardness is 424.6 HV_0.2. The vanadizing layer formed on the remelting surfaces is uniform and dense. The layers are mainly composed of VC_x phase and α-Fe/α′-Fe phase, the VC phase has the preferred orientation of (200) and (111) planes. There is a good metallurgical bonding between the vanadizing layer and the steel， and the thickness is 2.7 μm–12.15 μm, the microhardness is 2050.7 HV_0.2–2350.9 HV_0.2. When the laser remelting power is 300 W, the vanadizing layer is better in thickness, microhardness and average friction coefficient, the bonding force Lc between the vanadizing layer and the substrate is about 41.59 N, and the main failure mode is the spalling of the vanadizing layer. It can be concluded that laser remelting pre-treatment can greatly improve the hardness and wear resistance.

In this paper, the tribological behavior of Cu-SiO₂ composite against 1045 steel was studied. Based on the characterization of worn surface, worn subsurface and wear debris in morphology and composition, the friction layer effects on the tribological behavior of coupled materials and the wear mechanism were discussed. Abrasive wear and adhesive wear are the dominant mechanisms at the 0.56 m/s–1.12 m/s condition. Delamination wear and oxidation wear are the dominant wear mechanisms at the 1.68 m/s–2.24 m/s condition. Plastic and thermal deformation cause the evolution in morphology and structure of the tribolayer of Cu-SiO₂. There is a certain correlation between the friction coefficient and the variation in friction temperature during sliding wear of Cu-SiO₂ and 1045 steels. The addition of SiO₂ induces the accumulation of frictional heat at the friction interface, which leads to an increase in the average temperature of the contact surface and transfer.