| This thesis is aimed at two important parts in industrial production,shield machine cutter and propeller blade.Firstly, Fe-Co-Si-B?Fe-Co-Ni-Si-B?Fe-Mo-Ni-Si-B three different coatings were fabricated on 45 steel by laser cladding and laser remelting, amorphous nano-crystalline composite coatings were obtained.By a series of analysis and test, such as macroscopic observation, microstructure, phase analysis, hardness test, corrosion resistance and wear resistance, the optimal coating system was gained. And then take advantage of its excellent wear resistance and corrosion resistance, Fe- Mo- Ni- Si-B coating was prepared on the surface of the shield construction machine tool, and then we studied its microstructure and properties. On the other hand, in order to improve the corrosion performance of the propeller blade in the seawater, Ni-Cr-Cu coating was made on the surface of nickel aluminum bronze. To analysis the effect of different heat input on the microstructure and mechanical properties of the coating, different laser scanning speed were used. Then we came up with the optical laser parameters to improve the corrosion resistance.By laser cladding and remelting technology, Fe-Co-Si-B ? Fe-Co-Ni-Si-B ?Fe-Mo-Ni-Si-B three different coatings were fabricated on the surface of 45 steel,and the microstructure and properties of the coatings were studied. The laser remelting coating has thinner microstructure, more nanocrystalline organization and amorphous phase compared with the laser cladding coating. The micro-hardness of the coatings were about 4 ~ 5 times higher than the substrate.The hardness of the remelting coatings were higher than the cladding layers, especially the Fe- Mo- Ni- Si- B remelting layer, its micro-hardness was up to 1120 HV0.2. The polarization curve and impedance spectroscopy analysis showed that, the corrosion potential of the coatings were 400 m V- 500 m V higher compared with the 45 steel substrate. It means that the corrosion tendency of the coatings was greatly reduced. Remelting coating compared with not remelting coating, The corrosion current density of the remelting coatings decreased further than the cladding layers. The remelting layer Fe- Mo- Ni- Si – B has the best corrosion resistance, the corrosion potential of 248.44 m V, while the corrosion current density was 1.2763 x 10-6 Amps/cm2. The wear test results of Fe- Mo- Ni- Si- B coating showed that the laser cladding and remelting coating has much better wear resistance compared with the substrate, especially the laser remelting coatings.The failure analysis of the two shield machine showed that the main wear mechanism was abrasive wear and fatigue wear when working in a hard rock, and the import blade has better wear performance. Based on the wear mechanism and the work environment, it is recommended to use LD steel which has good wear resistance and fatigue resistance.Fe- Mo- Ni- Si- B coating was fabricated on the surface of shield machine tool by laser cladding. The coating had good metallurgical combination with the substrate. The corrosion potential of the single-channel cladding and multichannel were 40 m V and 101 m V higher than the substrate respectively. The corrosion current density also fell, especially overlapping layer. Its corrosion current density was 9.7466 × 10-8 Amps/cm2, increased two orders of magnitude compared with the matrix. The hardness of the multichannel lap coating is higher than that of the matrix, and the coating can significantly improve the wear resistance of the substrate. The mass loss of the multi-channel lap coating was about 1/5 of the matrix and the wear mechanism were abrasive wear and adhesive wear.Ni- Cr- Cu coating was fabricated on the surface of propeller blade material nickel aluminum bronze by laser cladding. Different laser scanning speed were chosen and the coating and the substrate can be a good metallurgical bonding. The coating was mainly composed of the solid solution of Ni, Cr, and Cu. The electrochemical corrosion test results showed that the corrosion potential of the coatings under different laser scanning speed were improved. The corrosion current density decreases, and the corrosion resistance of the coating was superior to the substrate. When the process parameters was 4 KW, 500 mm/min, the corrosion potential was the highest, 28.026 m V with the minimum corrosion current density, 6.3119 x 10-7 A/cm2, improve two orders of magnitude compared with the substrate. |
PDF Full Text Request