基于CA法钛合金激光快速成形晶粒生长模拟研究

发布时间：2018-11-04 10:54

【摘要】：TC4合金具有比重性好,比强度高以及抗氧化能力强等一系列优点,因此被广泛应用于航空航天、汽车制造及石油和化工等工业领域。激光快速成形技术可以控制熔池凝固过程中微观组织的生长方向和形态,有效提高钛合金的力学性能和高温性能。由于TC4钛合金激光快速成形过程中,熔池凝固具有非平衡高温瞬时性等特点,通过实验探究观察熔池微观组织形态具有一定难度。本文运用宏观与微观相结合的方法,将有限元法与胞自动机法相耦合的Cellular Automata-Finite Element(CA-FE)模型对TC4钛合金激光快速成形熔池凝固过程中的微观组织进行动态模拟。FE法对熔池温度场进行数值模拟,CA法模拟熔池凝固过程中的微观组织。基于温度场结果进行插值计算,带入微观元胞中,通过编程实现TC4熔池凝固的动态过程。在运用CA法模拟微观组织生长时,考虑晶粒形核的随机性和生长的确定性。用连续形核模型描述熔池形核过程,建立晶粒生长的等轴晶和柱状晶生长动力学模型。修正现有与元胞自动机模型相关的固相率和溶质分配算法,对熔池在均匀温度场下等轴晶生长以及柱状晶生长进行模拟,模拟结果与晶粒生长动力学基本吻合,显示晶粒生长指数接近理论值。将耦合的CA-FE模型带入,模拟非均匀温度场下熔池凝固过程中的晶粒生长。模拟结果显示:在固液相界面有大量晶粒形核,且各晶粒间存在竞争生长,晶粒组织以粗大的柱状晶为主。元胞网格越小,模拟晶粒形态越精确。与实验条件下熔池金相组织进行对比,结果显示熔池整体微观组织模拟情况与实际熔池凝固组织形貌基本一致,表明数值模拟结果具有可信度。
[Abstract]:TC4 alloys have many advantages such as good specific gravity, high specific strength and strong oxidation resistance, so they are widely used in aerospace, automobile manufacturing, petroleum and chemical industry. Laser rapid prototyping technology can control the growth direction and morphology of microstructure during the solidification process of molten pool and effectively improve the mechanical and high temperature properties of titanium alloy. In the process of laser rapid prototyping of TC4 titanium alloy, the solidification of molten pool has the characteristics of non-equilibrium high temperature transient, so it is difficult to observe the microstructure of molten pool through experiments. In this paper, the method of combining macro and micro is used. The Cellular Automata-Finite Element (CA-FE) model coupled with the finite element method and the cellular automata method is used to simulate the microstructure during the solidification process of the laser rapid prototyping of TC4 titanium alloy. The temperature field of the molten pool is numerically simulated by FE method. The microstructure of molten pool during solidification was simulated by CA method. Based on the results of temperature field interpolation, the dynamic process of solidification in TC4 molten pool was realized by programming. In the simulation of microstructure growth by CA method, the randomness of grain nucleation and the certainty of growth are considered. The continuous nucleation model is used to describe the nucleation process of molten pool and the kinetic model of equiaxed and columnar grain growth is established. The solids rate and solute distribution algorithms related to cellular automata models are modified to simulate the equiaxed crystal growth and columnar crystal growth in the molten pool under uniform temperature field. The simulation results are in good agreement with the grain growth kinetics. The grain growth index is close to the theoretical value. The coupled CA-FE model was introduced to simulate the grain growth during the solidification process of the molten pool under the inhomogeneous temperature field. The simulation results show that there are a large number of nucleation grains at the solid-liquid interface, and there are competing growth among the grains, and the grain structure is dominated by coarse columnar crystals. The smaller the cell mesh is, the more accurate the simulated grain morphology is. Compared with the experimental results, the results show that the simulation of the whole microstructure of the molten pool is basically consistent with the morphology of the solidified microstructure of the actual molten pool, which indicates that the numerical simulation results are reliable.
【学位授予单位】：沈阳航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.23;TG665

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