Inconel 718合金选区激光熔化流场及微熔池传质的研究
发布时间：2019-02-24 15:24
【摘要】：为了研究SLM快速成型Inconel 718粉末中的流场分布及变化过程,建立了三维有限元分析模型。在计算中考虑了重要的物理现象,从粉末床到实体的过渡、与温度有关的材料的物性参数、由温度梯度产生的表面张力、移动的呈高斯分布的激光热源。并对试样进行了流场流动实验验证以及Inconel 718合金中Nb元素偏析实验,最终得到结论。模拟结果发现,热源在移动的过程中,由于热源移动的影响,温度云图呈现彗星尾巴的形状。熔池上表面存在温度梯度,且前侧温度梯度大于熔池后侧温度梯度,这是由于前端熔池范围小,液态金属间的对流换热较少,与固体金属间的热传导也较少,使前端温度梯度增加。温度梯度的产生使熔池上表面存在表面张力梯度,熔池中流体远东的主要驱动力是在熔池表面由于表面张力梯度产生的Marangoni对流。熔体流动速度与激光扫描参数密切相关。激光功率越大或者扫描速度和扫描间距越小,熔体流动的最大速度增加,熔池中的涡流尺寸增大,即熔池中传质越好。而且多道扫描比单道扫描的流动速度大,这是由于受相邻轨道的热影响的结果。在不同工艺参数下,对熔池的Nb元素偏析现象进行了实验分析。研究发现,随着激光功率的增大或者扫描速度和扫描间距的减小,熔池表面的Nb元素浓度低,分布更均匀,即偏析现象减弱。因为SLM属于超快速凝固,因此熔池在凝固过程中,抑制了固相和液相中的扩散,导致凝固后形成的固相中Nb元素的分布与液相时相似。模拟中传质随参数的变化规律和实验中的偏析变化规律结果一致。
[Abstract]:In order to study the distribution and variation of flow field in Inconel 718 powder of SLM rapid prototyping, a three dimensional finite element analysis model was established. Important physical phenomena are taken into account in the calculation, including the transition from powder bed to solid, the physical properties of temperature-related materials, the surface tension generated by temperature gradient, and the moving laser heat source with Gao Si distribution. The flow field flow experiments and segregation of Nb elements in Inconel-718 alloy were carried out. Finally, the conclusion was obtained. The simulation results show that the temperature cloud shows the shape of the comet tail in the process of heat source movement due to the influence of heat source movement. There is a temperature gradient on the upper surface of the molten pool, and the temperature gradient on the front side is larger than that on the back side of the molten pool. This is due to the small range of the front pool, the less convection heat transfer between liquid metals and the less heat conduction between liquid metals and solid metals. Causes the front end temperature gradient to increase. The surface tension gradient exists on the surface of the molten pool due to the temperature gradient. The main driving force of the fluid far East in the molten pool is the Marangoni convection on the molten pool surface due to the surface tension gradient. The melt flow velocity is closely related to the laser scanning parameters. The larger the laser power or the smaller the scanning speed and the scanning distance, the greater the maximum velocity of melt flow and the larger the eddy current size in the molten pool, that is, the better the mass transfer in the molten pool. Moreover, the flow velocity of the multi-channel scan is higher than that of the single-pass scan, which is due to the heat effect of the adjacent orbit. The segregation of Nb elements in molten pool was analyzed experimentally under different process parameters. It is found that with the increase of laser power or the decrease of scanning speed and scanning distance, the concentration of Nb elements on the surface of the molten pool is lower and the distribution is more uniform, that is, the segregation phenomenon is weakened. Because SLM belongs to super rapid solidification, the diffusion of Nb in solid phase and liquid phase is restrained during solidification in the molten pool, and the distribution of Nb element in solidified solid phase is similar to that in liquid phase. The variation of mass transfer with parameters in simulation is consistent with that of segregation in experiments.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG292
，
本文编号：2429675
[Abstract]:In order to study the distribution and variation of flow field in Inconel 718 powder of SLM rapid prototyping, a three dimensional finite element analysis model was established. Important physical phenomena are taken into account in the calculation, including the transition from powder bed to solid, the physical properties of temperature-related materials, the surface tension generated by temperature gradient, and the moving laser heat source with Gao Si distribution. The flow field flow experiments and segregation of Nb elements in Inconel-718 alloy were carried out. Finally, the conclusion was obtained. The simulation results show that the temperature cloud shows the shape of the comet tail in the process of heat source movement due to the influence of heat source movement. There is a temperature gradient on the upper surface of the molten pool, and the temperature gradient on the front side is larger than that on the back side of the molten pool. This is due to the small range of the front pool, the less convection heat transfer between liquid metals and the less heat conduction between liquid metals and solid metals. Causes the front end temperature gradient to increase. The surface tension gradient exists on the surface of the molten pool due to the temperature gradient. The main driving force of the fluid far East in the molten pool is the Marangoni convection on the molten pool surface due to the surface tension gradient. The melt flow velocity is closely related to the laser scanning parameters. The larger the laser power or the smaller the scanning speed and the scanning distance, the greater the maximum velocity of melt flow and the larger the eddy current size in the molten pool, that is, the better the mass transfer in the molten pool. Moreover, the flow velocity of the multi-channel scan is higher than that of the single-pass scan, which is due to the heat effect of the adjacent orbit. The segregation of Nb elements in molten pool was analyzed experimentally under different process parameters. It is found that with the increase of laser power or the decrease of scanning speed and scanning distance, the concentration of Nb elements on the surface of the molten pool is lower and the distribution is more uniform, that is, the segregation phenomenon is weakened. Because SLM belongs to super rapid solidification, the diffusion of Nb in solid phase and liquid phase is restrained during solidification in the molten pool, and the distribution of Nb element in solidified solid phase is similar to that in liquid phase. The variation of mass transfer with parameters in simulation is consistent with that of segregation in experiments.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG292
，
本文编号：2429675
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