电子束选区熔化增材制造熔池演化多尺度模拟

Multi-scale numerical simulation of molten pool evolution process for electron beam selective melting

电子束选区熔化增材制造是金属增材制造领域的重要发展方向。为了理解和控制电子束扫描过程中熔池流场与温度场演化规律,并进一步探明和预测凝固成形件的微观组织形成过程,提高零件的冶金质量和力学性能,本文采用基于格子玻尔兹曼方法及有限体积法混合格式的三维传热传质模型,对熔池的形貌尺寸、温度场、流场及相场演化进行模拟。结果表明,当电子束扫描速度从800 mm/s增加到1600 mm/s时,冷却速度从0.19 K/μs增加到0.45 K/μs,温度梯度从0.99 K/μm增加到3.72 K/μm。进一步采用基于格子玻尔兹曼方法的微观枝晶生长模型探究微观组织形成机制,研究发现,固液界面处出现沿温度梯度方向生长的柱状晶,且电子束扫描速度越大,柱状晶生长越快,熔体流动可在一定程度上促进柱状晶的生长。

The electron beam selective melting additive manufacturing is an important development direction in metal additive manufacturing.In order to understand and control the evolution law of the flow field and temperature field in the molten pool during electron beam scanning,further explore and predict the microstructure formation process of solidification parts,and improve the metallurgical quality and mechanical properties of formed parts,a three-dimensional comprehensive heat and mass transfer model based on lattice-Boltzmann method and finite volume method was adopted in this paper.The results show that,when the electron beam scanning speed increases from 800 mm/s to 1600 mm/s,the cooling rate increases from 0.19 K/μs to 0.45 K/μs,and the temperature gradient increases from 0.99 K/μm to 3.72 K/μm.Furthermore,the micro dendrite growth model based on the lattice-Boltzmann method was used to explore the formation mechanism of microstructure.The results show that the columnar dendrite grows along the temperature gradient direction at the solid-liquid interface,and the higher the scanning speed of the electron beam,the faster the columnar dendrite grows.In addition,the melt flow promotes the columnar dendrite growth to a certain extent.