【作者】 严卫东；

【导师】 刘林；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2002， 博士

【摘要】 金属铸件凝固过程中晶粒组织的控制十分重要，这是因为晶粒组织决定着铸件的力学性能和使用性能。尽管传统的晶粒组织控制的试验方法很直观，可操作性强，应用广泛，但它无法揭示与晶粒组织形成有关的物理机理，而且要耗费大量人力、物力和时间。而近年来逐步兴起的计算机模拟方法能弥补试验方法的不足，越来越受到人们的重视。本文模拟了简单二元枝晶合金A1-4wt％Cu合金和复杂多元合金K4169高温合金铸件在其凝固过程中晶粒组织的形成过程，计算了在不同铸造工艺下其凝固时晶粒密度和平均晶粒尺寸的变化，并在计算机屏幕上显示了晶粒形核与生长的动态过程，实现了晶粒形成的可视化。 1．采用有限差分法分别解用热焓法处理结晶潜热的直角坐标系二维不稳定热传导方程和圆柱坐标系一维不稳定热传导方程，利用Fortran语言编程，模拟了A1-4wt％Cu合金铸造试样、K4169高温合金圆柱锭和叶片某一横截面凝固过程中温度场的变化，它正确地反映了在不同铸造工艺条件下合金铸件横截面上温度场的变化规律，其中模拟的A1-4wt％Cu合金铸造试样某一横截面凝固过程中温度场变化与其实测的温度场变化吻合较好。 2．通过固相分数，将合金铸件凝固温度场模拟及其连续形核模型、枝晶尖端生长的动力学模型相耦合，利用Fortran语言编程，计算了A1-4wt％Cu合金铸造试样、K4169高温合金圆柱锭和叶片凝固时晶粒组织的特征值，包括晶粒密度和平均晶粒尺寸，计算结果和实验结果吻合较好。 3．采用二维Cellular Automaton方法，利用Fortran语言编程，在计算了Al-4wt％Cu合金铸造试样、K4169高温合金圆柱锭和叶片凝固时晶粒组织特征值的基础上，用计算机画出了这些铸件某一横截面晶粒形核与生长的图像，实现了在计算机屏幕上动态显示晶粒形核和生长过程，所模拟横截面上的晶粒组织金相照片和计算机上画出的铸件凝固结束后晶粒组织图相似。 4．通过大量K4169高温合金圆柱锭熔模铸造实验，确定了不同浇注温度(其它铸造工艺参数相同)下K4169高温合金连续形核模型的参数。在此基础上，利用Fortran语言编程，计算了不同浇注温度下K4169高温合金圆柱锭凝固过程中晶粒组织的特征值，并实现了在计算机屏幕上晶粒形核和生长的可视化，模拟结 摘 要果和实验结果吻合较好。 S，通过大量＊4169高温合金圆柱锭熔模铸造实验，确定了不同化学沦纠M’；铸造工艺条件（加入不同细化剂）下 K4 69高温合金连续形核模型的参数。在此基础上，利用 Fortran语言编程，计算了不同细晶铸造工艺条件下 K4 69高温合金圆柱锭凝固过程中晶粒组织的特征值，井实现了在计算机屏幕上晶粒形核和生长的可视化，模拟结果和实验结果吻合较好。 6．根据等轴枝晶生长过程的物理机制，改进了等轴枝晶生长的溶质扩散模型。模型除了描述了晶粒的生长，同时还描述了枝晶臂的粗化。因此它除了能够计算球状枝晶固相分数变化，还可以比较准确地计算典型的等轴枝晶固相分数变化，放松了原模型假设中一些最严格的限制，使它能够得到更广泛的应用。 7二 在模拟了 K4 69高温合金圆柱锭凝固过程中晶粒组织形成的基础上，利用 Fortran语言编程，计算了传统熔模铸造工艺和优化的细晶铸造工艺下 K4 69高温合金叶片凝固过程中晶粒组织的特征值，并实现了在计算机屏幕上晶粒形核和生长的可视化，模拟结果和实验结果吻合较好。更多还原

【Abstract】 The control of the grain structure is of primary importance in many solidification processes of castings,because the grain structure has influence on their mechanical properties and operating performances. Although the experiment-based method adopted for the control of the grain structure is widely used for its visualization and simplicity,it does not give much insight into the physical mechanisms responsible for grain structure formation,it also expends much time and money. The computer simulation method that is rising recently has been paid more and more attention because it can counteract the experiment-based method’s weaknesses. In this thesis,the grain structure formation in solidification of Al-4wt%Cu alloy and superalloy K4169 castings has been simulated by computer. The evolution of their grain density and grain size during solidification was calculated under various founding processes. The grain nucleation and growth pictures were displayed on the computer screen,the visualization of grain formation by computer has been achieved.1. Using FDM Fortran program,the temperature fields on a cross section of Al-4wt%Cu alloy founding samples,superalloy K4169 cylinder ingots and superalloy K4169 blades were simulated through solving the heat diffusion equation with enthaply formulation. It reflected temperature evolution on the cross section of castings under various founding processes correctly. The simulated results of Al-4wt%Cu alloy founding samples agree well with the measured ones.2. Using the fraction of solid,the simulation of temperature fields,the continuous nucleation model and growth kinetics model of the dendritic tip were coupled to calculate grain structure features of Al-4wt%Cu alloy founding samples,superalloy K4169 cylinder ingots and superalloy K4169 blades. The calculated results agree well with the measured ones.3. Based on a two-dimensional Cellular Automaton technique and the grain structure features of Al-4wt%Cu alloy founding samples,superalloyK4169 cylinder ingots and superalloy K4169 blades,the grains nucleation and growth of these castings were displayed on computer screen dynamically,the visualization of grain formation by computer has been achieved.4. Through investigations for a great number of investment castings of superalloy K4169 cylinder ingots,the continuous nucleation model parameters of superalloy K4169 at different pouring temperatures have been deduced. The grain structure features of superalloy K4169 cylinder ingots during solidification at different pouring temperatures were computed. The visualization of grain nucleation and growth by computer has been achieved. The calculated effect of the pouring temperature on the resultant grain structure agrees well with experimental observations.5. Through investigations for a great number of investment castings of superalloy K4169 cylinder ingots,the continuous nucleation model parameters of superalloy K4169 under various refining processing have been deduced. The grain structure features of superalloy K4169 cylinder ingots during solidification under various refining processing were computed. The visualization of grain nucleation and growth by computer has been achieved. The calculated effect of refiner on the resultant grain structure agrees well with experimental observations.6. In the light of physical mechanism of equiaxed dendrite growth,solute diffusion models for equiaxed growth was improved. The improved model not only describes grain growth,but also describes coarsening of dendrite arms. By this model,the solid-fraction evolution of the globulitic dendritic can be calculated,the solid-fraction evolution of the star dendritic can also be calculated accurately. So this model can be used more widely.7. On the basis of simulation of grain structure formation in solidification of superalloy K4169 cylinder ingots,The grain structure features of superalloy K4169 blades under conventional investment castings and optimal refining processing were computed. The visualization of grain nucleation and更多还原