Research On Key Technologies Of Partial Porous Externally Pressurized Gas Bearing

High temperature erosion or ablation wear is a major failure reason in gun barrels. It cannot only cause material loss, but also cause serious safety accidents, such as gun bore premature. To solve these problems and prolongs the service life of gun barrels, we prepared ceramic-metal composite wear resistance coatings, using advanced thermal diffusion technique and laser cladding technique.The thermal diffusion composite coating is prepared in the inner wall of the pipe. The coating thickness is 30μm, and the surface is flat and smooth. Due to particle dispersion strength of the BN ceramic phase, the hardness of the coating is more than 1100 HV. In the gunpowder explosion and ablation experiment, obvious plastic deformation and shear cracks appeared in the inner wall of the pipe, but the coating had still not crumbled off, which shows a high bonding strength with the substrate and ablation resistance of the coating. The NiCr-Cr3C2 coatings with different Ni content were also prepared using laser cladding technology. The coatings with the thickness of 1500μm have 200-300μm wide Element diffusion regions, it illustrates good metallurgical bonding exits between the coatings and substrate. With the increase of Ni content, the pores and cracks become less, but the average hardness decreases rapidly. Phase analysis also shows there are Cr3C2, Cr7C3 and Cr23C6 ceramic phases in the coatings, these phases make the microstructure change and the hardness of coatings increase.The High temperature erosion experiment shows that the mechanism of pulsed electro-deposition coating is quite different with the laser cladding layers. It was found that the electro-deposition coating has more characteristics of brittle materials, but their High temperature erosion resistant performance is better than the substrate. To the laser cladding coatings, with the increase of Ni content, the erosion wear ratio decrease before increase, when Ni content is in 35%,the coating has the best thermal erosion resistant performance.