| HU Zhao-wei,LI Wen-ge.Process Research of In-situ Synthesis of Mo2NiB2 Coating by Laser Clad-ding[J],46(8):1-6 |
| Process Research of In-situ Synthesis of Mo2NiB2 Coating by Laser Clad-ding |
| Received:January 18, 2017 Revised:August 20, 2017 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2017.08.001 |
| KeyWord:laser cladding in-situ synthesis Mo2NiB2 process parameters solidification |
| Author | Institution |
| HU Zhao-wei |
Shanghai Maritime University, Shanghai , China |
| LI Wen-ge |
Shanghai Maritime University, Shanghai , China |
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| Abstract: |
| Mo2NiB2 ternary boride metal-base ceramic is of excellent wear resistance and corrosion resistance, and can be widely used in marine corrosion prevention covering ships, marine pipelines, ocean platform and harbor facilities. In-situ reaction produces chemical reaction under certain conditions by using different elements, and forms one or more reinforced phase(s) in metal substrate. Laser cladding in-situ synthesis method was a new method of preparing ternary boride coating on the surface of carbon steel. High laser energy was used as excitation condition of in-situ reaction to produce superfine reinforced ceramic phase directly on the surface of carbon steel. As laser cladding is a quick heating and cooling technology, its process become more complex once being combined with in-situ synthesis reaction technology. Therefore, technological parameter had significant effects on coating. Calculation of solidification characteristic parameter contributed to selection and optimization of technological parameters. A coating containing Mo2NiB2 reinforced phase was prepared on the surface of carbon steel by laser cladding in-situ synthesis method. Microstructure of the coating was analyzed with metallographic microscopy, scanning electron microscope and X ray diffractometer. Temperature field of cladding process was simulated with ANSYS and then solidification characteristic parameters, i.e., shape control factors, were calculated. Microstructure analysis showed that refined and uniform microstructure was obtained when laser power was 2500 W, scanning speed was 1.5 mm/s and thickness of precoated layer was 1 mm. White part in the coating was Mo2NiB2 and gray parts were Fe, Ni solid solutions. Site where the coating was bond to the substrate grew in the form of planar crystal, and then grew away from the interface in the mode of dendrite. Calculation of temperature field and solidification characteristic parameter showed that temperature gradient reached 105 ℃/m, shape control factor was at least 109 (℃•s)/m2. Dendritic structure tends to be refined and and shape control factor (K) increases sharply as laser power increased. When K is 3×109~5×109 (℃•s)/m2, the solidification structure is planar crystal, and appears as “white bright band”; when K is over 7×109 (℃•s)/m2, the solidification structure was dendrite crystal; when K is 13×109 (℃•s)/m2, the crystalline grain is refined. |
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