| LUO Jian,XIE Song-wei,MAO Jia-zhi,WANG Liang,ZHANG qun-li,GE hong-hao,YAO Jian-hua.Effect of a Steady Magnetic Field on the Macro-segregation and Element Diffusion of Laser Cladding Cobalt-based Alloy[J],51(12):320-328, 349 |
| Effect of a Steady Magnetic Field on the Macro-segregation and Element Diffusion of Laser Cladding Cobalt-based Alloy |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.12.033 |
| KeyWord:laser cladding steady magnetic field molten pool macro-segregation element diffusion |
| Author | Institution |
| LUO Jian |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
| XIE Song-wei |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
| MAO Jia-zhi |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
| WANG Liang |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
| ZHANG qun-li |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
| GE hong-hao |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
| YAO Jian-hua |
College of mechanical Engineering,Institute of Laser Advanced Manufacturing Zhejiang University of Technology, Hangzhou , China;Collaborative Innovation Center of High-end Laser Manufacturing Equipment Co-sponsored by Ministry and Province, Hangzhou , China |
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| Abstract: |
| The substrate material was 316L austenitic stainless steel and the CL (Cladding layer) material was Cobalt-based alloy powder. In order to avoid the interference of the magnetic field in the LC (Laser cladding) process, both the substrate and the cladding powder are non-ferromagnetic. Cobalt-based coatings were prepared by LC assisted with a steady magnetic field. The maximum magnetic flux intensity is 1.8 T. During the experiment, the sample was kept stationary, while the laser head was moved to scan the substrate. The powder was injected into the molten pool through carrier gas with the laser coaxially. The surface of the corroded sample is observed with Optical metallographic microscope (OM), Scanning electron microscope (SEM), and the composition of the CL is analyzed by Energy dispersive spectrometer (EDS). The morphology of the molten pool changes obviously when the steady magnetic field is applied. With the increase of the magnetic flux density, the electromagnetic damping gradually increases, which reduces the convexity of the solidification line of the molten pool and made the bottom of the molten pool smoother. Without magnetic field, the macro-segregation moves with molten pool fluid, which is evenly distributed in the upper region of the CL after sufficient stirring and diffusion. Since the fluid velocity at the bottom of the molten pool is lower than that of the upper layer, the macro-segregation at the bottom of the molten pool is more obvious. The proportion of the macro-segregation area in the CL changes from low to high from the surface to the bottom. With the magnetic flux density increases, the proportion of the macro-segregation area in the entire CL gradually increases. With magnetic field, due to the damping effect on fluid flow, the macro-segregation can be completely retained in the molten pool without being dispersed. The zone without macro-segregation maintains a high content of Co and a low content of Fe. When there is no magnetic field, the Fe element at the zone of macro-segregation is diffused to the surrounding area, resulting in an increase of Fe element the zone of without macro-segregation. When the magnetic field is added, the Fe content in the zone around the macro-segregation is significantly reduced compared with the case without magnetic field. It is indicated that the diffusion of Fe element at the macro-segregation is suppressed by the steady magnetic field. Since the liquidus temperature TLB (1 370 ℃) of the powder alloy is lower than the liquidus temperature TLC (1 440 ℃) of the matrix, when the liquid matrix metal is brought into the molten pool with low temperature by convection, it will be quickly solidified in the molten pool. With the increase of magnetic flux density, the Hartmann number of the molten pool gradually increases and the distribution is uneven. Due to the lower temperature and higher conductivity at the bottom of the molten pool, the Hartmann number at the bottom of the molten pool is higher than the top of the molten pool. It is shown that the equivalent viscosity at the bottom of the molten pool is higher than that at the top of the molten pool. This phenomenon leads to severe macro-segregation at the bottom of the molten pool and suppresses the diffusion of macro-segregation to the surrounding area. The steady magnetic field suppresses the diffusion of macro-segregation in the CL, reduces the dilution of solute elements, and obtains the CL which is closer to the cladding powder. |
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