电弧增材成形单道两层熔积过程中的晶粒生长模拟

晶粒生长的数值模拟是研究复杂微观组织演变的重要手段，现有的研究较少涉及电弧增材成形中晶粒生长的数值模拟。采用有限元和元胞自动机方法建立了碳钢电弧增材成形过程的宏观传热和微观组织演变的耦合模型，模拟单道第两层熔积的熔池凝固过程中晶粒动态演变过程。模拟结果显示，单道第一层熔积熔池凝固过程中晶粒从熔合线位置形核后向熔池中心生长，在温度梯度方向与枝晶臂优先生长方向的共同作用下，枝晶呈现竞争生长，晶粒优先生长方向与温度梯度方向一致的晶粒生长更快，部分晶粒生长被抑制，最终形成交错、完全粗大的柱状晶组织，枝晶之间出现溶质富集的现象；单道第二层熔积的晶粒在上一层粗大柱状晶基础上形核并生长，随后的生长过程与第一层类似，第二层熔积时熔池温度梯度方向的改变导致晶粒的主要生长方向与第一层之间有一定夹角。与模拟相同成形工艺的成形试样金相照片验证了模拟结果。研究结果可为电弧增材成形微观组织控制以及后续工艺规划提供依据和参考。

Simulation of Grain Growth in Single-pass Two-layer Deposition of Arc Welding Based Additive Forming Process

The numerical simulation of grain growth is an important way to study the evolution of complex microstructure. Studies are less concerned with numerical simulation of grain growth in arc welding based additive forming(AWAM) process. A coupling model of macroscopic heat transfer and microstructure evolution in AWAM process is established by finite element method and cellular automata method. Then, the dynamic evolution of grains during the solidification process of the molten pool is simulated. The simulated results show that the grains nucleate at the fusion line and then grow toward the molten pool center in the first-layer deposition. Under the influence of the temperature gradient direction and crystallographic orientation of the dendritic arms, the competition between the grains becomes strong. When the crystallographic orientation coincides with the temperature gradient direction, the grain growth faster, and the others are inhibited. Ultimately, the grain morphology is characterized by staggered and coarse columnar grains. In adition, the solute enrichment phenomenon appears between the grains. In the second-layer deposition, the grains nucleate on the columnar grains of upper layer, and the subsequent growth process is similar to the upper layer. Beacause the change of temperature gradient direction of molten pool in the second-layer deposition, there is a lilte angle between the main growth direction of the grains between the first-layer and second-layer. The simulated results are verified by metallographic photograph of the experimental test. The conclusions of the above study can provide the basis and reference for the microstructure control and process planning of AWAF process.