【摘要】：為了研究SLM快速成型Inconel 718粉末中的流場分布及變化過程,建立了三維有限元分析模型。在計算中考慮了重要的物理現(xiàn)象,從粉末床到實體的過渡、與溫度有關的材料的物性參數(shù)、由溫度梯度產(chǎn)生的表面張力、移動的呈高斯分布的激光熱源。并對試樣進行了流場流動實驗驗證以及Inconel 718合金中Nb元素偏析實驗,最終得到結(jié)論。模擬結(jié)果發(fā)現(xiàn),熱源在移動的過程中,由于熱源移動的影響,溫度云圖呈現(xiàn)彗星尾巴的形狀。熔池上表面存在溫度梯度,且前側(cè)溫度梯度大于熔池后側(cè)溫度梯度,這是由于前端熔池范圍小,液態(tài)金屬間的對流換熱較少,與固體金屬間的熱傳導也較少,使前端溫度梯度增加。溫度梯度的產(chǎn)生使熔池上表面存在表面張力梯度,熔池中流體遠東的主要驅(qū)動力是在熔池表面由于表面張力梯度產(chǎn)生的Marangoni對流。熔體流動速度與激光掃描參數(shù)密切相關。激光功率越大或者掃描速度和掃描間距越小,熔體流動的最大速度增加,熔池中的渦流尺寸增大,即熔池中傳質(zhì)越好。而且多道掃描比單道掃描的流動速度大,這是由于受相鄰軌道的熱影響的結(jié)果。在不同工藝參數(shù)下,對熔池的Nb元素偏析現(xiàn)象進行了實驗分析。研究發(fā)現(xiàn),隨著激光功率的增大或者掃描速度和掃描間距的減小,熔池表面的Nb元素濃度低,分布更均勻,即偏析現(xiàn)象減弱。因為SLM屬于超快速凝固,因此熔池在凝固過程中,抑制了固相和液相中的擴散,導致凝固后形成的固相中Nb元素的分布與液相時相似。模擬中傳質(zhì)隨參數(shù)的變化規(guī)律和實驗中的偏析變化規(guī)律結(jié)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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG292
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本文編號：2429675