目的 探究在304LN不锈钢表面上激光沉积Stellite 6合金过程中的多元素传输机制.方法 采用流体体积法VOF(Volume of Fluid),建立气-液两相传热传质激光沉积模型.模型中使用改进VOF法对熔池表面进行追踪,结合多组分传输模型与熔凝杠杆原则(Lever Rule),对异质材料熔覆界面的多元素传输进行模拟,采用扫描电子显微镜(SEM)与能谱仪(EDS)观察组织结构和元素分布,对比模拟结果分析多组沉积层宏观形貌和元素分布特征.结果 沉积过程中,熔池的流动与材料导热对温度的传输起着重要作用,前端对流不断地将已熔化的基材金属运输至熔池中部,后端对流则将卷积的Fe元素和Co元素进一步混合.最终沉积层的宏观形貌平均误差为2.67％,主要元素Fe、Co、Cr的质量分数误差分别为0.64％、1.27％、0.31％.结论 Fe元素浓度整体区域分布相对均匀,但在沉积层底部,Fe元素浓度迅速升高,Co元素浓度随沉积深度加深逐渐降低,Cr元素在沉积层中部富集的分布特性.该优化后的模型可以准确模拟异质合金沉积过程中的温度场、流场与质量传输过程.
Numerical Simulation of Multi-element Transport Behavior during Surface Deposition of Heterogeneous Alloy in 304LN
The work aims to investigate the multi-element transport mechanism during laser deposition of Stellite 6 alloy on the surface of 304LN stainless steel. In this study,the Volume of Fluid (VOF) method was employed to simulate the heat conduction and flow characteristics of the melt pool,and the multi-element transport processes,aiming to investigate the principles of multiple elements diffusion in the deposited layer and the distribution characteristics of strengthening phases. Firstly,a two-phase solidification 2D model based on the VOF method was developed,taking into account the element transport model and the melting-solidification lever rule. The model was used to investigate the distribution mechanism of three main elements during deposition of Stellite 6 cobalt alloy powders on a 304LN stainless steel substrate. Then,transient temperature distribution and flow field data at different locations were obtained. Finally,the calculated geometrical shapes and element distributions under different processing parameters were found to be in good agreement with experimental results. The accurate identification of the liquid-vapor interface area was achieved by tracking the gradient differences of second phase volume fraction in the computational grid. Here,the thermal properties of the material were defined based on a mixture rule,taking into account the reaction time of the mechanical arm servo. Compared to multiple experimental results,the average geometric shape error was 2.67％,and the mass score error of the main elements was 0.64％ (Fe),1.27％ (Co),and 0.31％ (Cr). Moreover,a comet tail-like temperature field was observed at the rear end of the melt pool,resulting in Marangoni convection caused by temperature gradients,and leading to the further mixing of various elements. At the same time,the distribution characteristics of three main elements in the deposited layer varied. Due to the effect of Marangoni convection,the distribution of Fe element was relatively uniform in the overall region,but the concentration sharply increased in the bottom layer. While,the concentration of Co element gradually decreased from top to bottom due to the deposition process,with a significant decrease near the bottom of the deposited layer. The concentration of Cr element exhibited a slight enrichment in the middle of the deposited layer due to the solidification of the strengthening phase,resulting in a slight increase in hardness in this region. The effect of temperature fields,flow fields,and solidification phase transformations on the distribution of multiple elements during the deposition process is studied. By comparing the results,it is found that the overall distribution of various elements is relatively uniform,with only significant variations occurring at the bottom of the melt pool. Furthermore,variations in processing parameters have a significant impact on the content of strengthening phases,which leads to substantial differences in the mechanical properties of the deposited layer. The developed model demonstrates excellent simulation performance in replicating the deposition experiments,providing an effective theoretical reference for controlling the size of the dilution region and the distribution of each element.
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