【作者】 丁雨田；

【导师】 许广济；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2005， 博士

【摘要】 综述了金属凝固过程微观组织模拟从确定性模型、概率模型到相场法的发展过程和方法,以及各种模型存在的问题。提出Cellular Automation(元胞自动机,简称CA)概率模型由于考虑了晶体生长的择优取向,具有明确的物理背景,适合于模拟热型连铸凝固过程微观组织演化过程。 试验研究了热型连铸凝固过程微观组织演化机理。提出在热型连铸凝固过程中组织演化经历了三个阶段,即晶粒迅速淘汰阶段、晶粒缓慢淘汰阶段和单晶生长阶段。组织演化过程本质上是由液固界面的形状所控制的,凸向液体的液固界面形状有利于晶粒的淘汰,得到单晶体,而液固界面的形状受连铸速度的影响,随着连铸速度的增加,液固界面形状发生凸-平-凹转变。 应用Monte Carlo方法模拟了单向凝固的组织形成过程。该方法能够模拟出单向凝固条件下柱状晶的竞争生长,而且模拟结果与实际组织具有一定的相似性。但Monte Carlo方法没有考虑晶粒的择优取向等定向凝固中的一些关键参数,缺乏明确的物理依据。尽管如此,Monte Carlo方法还是可以用来定性的模拟定向凝固的组织形成,对于各项工艺参数的分析提供一定的参考价值。 应用热型连铸凝固热传输过程的显示交替差分数值模拟方法和微观组织模拟的CA方法,将宏观温度场模拟和微观组织模拟耦合,建立了微宏观统一的二维和三维微观组织模拟耦合模型。采用该模型,针对纯Cu金属的热型连铸,模拟研究了共组织演化过程及热型连铸中各种工艺参数对组织演化的影响。研究表明,尽管微观组织形成的二维模拟结果能够反映热型连铸凝固过程组织形成的特点,与实际试验结果有较好的一致性,但是二维模拟结果显示的是圆柱体铸棒中心轴对称面上的微观组织,考虑到微观组织的不对称性和随机性,二维模拟结果并不能准确地反映热型连铸凝固过程组织演化的结果,更准确地模拟应该不仅能显示轴向微观组织,而且也能显示横断面的微观组织,这就必须进行微观组织的三维模拟,只有这样,才能完全了解热型连铸微观组织的演化过程。三维微观组织模拟,可显示热型连铸凝固过程微观组织的晶粒形貌,再现晶粒的生长过程。对热型连铸中不同工艺条件下组织演化的模拟研究表明:连铸速度对固液界面的形状、位置和晶粒淘汰的影响较大。随着连铸速度的增大,固液界面由凸向液相区逐渐变为平界面甚至是凸更多还原

【Abstract】 The paper reviews the deterministic model—stochastic model— phase-field model development and techniques of microstructure simulation of metal solidification process, as well as shortcomings for various models, argues that the Cellular Automation stochastic model suits to simulate microstructure evolvement of solidification process in the heated mould continuous casting(HMCC) as the model involves the preferential direction of crystal growth, with its obvious physical setting.The experiment studies the mechanism of microstructure evolvement and brings forward the three stages of structure evolvement in solidification process: 1) rapid selective elimination of crystal articles, 2) slow selective elimination of crystal articles and 3) single crystal growth. Structure evolvement lies on the shape of liquid-solid interface. Protruding liquid-solid interface is propitious to the selective elimination of crystal articles, gaining single crystals. And the shape of liquid-solid interface rests with casting speed, varying from convexity to plane to concave with the increase of it.Monte Carlo method can simulate structure formation process of unidirectional solidification, demonstrating the competitive growth of column-shaped crystals in unidirectional solidification, and the simulation result is definitely similar to the actual structure. Monte Carlo method, devoid of specific physical basis, however, does not touch upon some key parameters in unidirectional solidification such as the preferential direction of crystal growth. Still, Monte Carlo Method can be used as qualitative simulation technique for structure formation in unidirectional solidification, with the supply of definite reference value for the analyses of various technical parameters.With displaying alternative difference numerical method of heat transfer process and Cellular Automation of microstructure simulation, a combinative macro-microcosmic 2D and 3D coupling model of microstructure simulation can be established by couplingmacro temperature field simulation with microstructure simulation. With pure metal Cu as a subject, this model technique is used to work over its (Cu) structure evolvement process and to test the effect on it of various technical parameters. The research indicates that 2D simulation results come to reflect the characteristics of structure evolvement as does HMCC process and appear to better accord with actual experiment results. On the other hand, 2D simulation results can show microstructure in the transect of casting road only and cannot well and truly reflect the process of structure evolvement due to the dissymmetry and randomness of microstructure. Even more true simulation is not only to show microstructure in the vertical section, but of microstructure transect, so there must be great necessity of carrying out 3D simulation, with which the evolvement in the HMCC process can be completely and truly described and shown. 3D microstructure simulation can display and reproduce crystals. Simulation research of structure evolvement at different technical levels in HMCC indicates that the casting speed has obvious effect on liquid-solid interface concerning its shape, position and competition of crystals growth. With the increase of casting speed, liquid-solid interface changes from convexity liquid appearance to smooth plane, even to convexity solid appearance, and the higher the mould temperature is, the stronger the competition of crystals is. While cooling intensity has not too effect on the competition of crystals, higher mould temperature and corresponding stronger cooling intensity can get casting road with smooth surface and not to be pulled leak and part in casting process. Cellular Automaton Model for simulating microstructure formation has specific physical property, with the simulation result very adjacent to the true situation, which convincingly makes clear that Cellular Automaton Model is a feasible simulation technique for microstructure simulation.更多还原