DD6高温合金定向凝固枝晶生长的数值模拟研究_张航

粒生长捕获过程包括处理枝晶生长速度, 考虑热过 冷、成分过冷及界面各向异性等因素[16~19]. 基于上述 模型, 国内外学者[17~24] 广泛开展了枝晶凝固的数值 模拟研究, 同时部分学者[23,25,26] 开展了透明合金枝晶 生长过程的实验研究.
近年来, 相场方法和元胞自动机(CA)方法在模 拟枝晶形貌及演化方面得到了快速发展: 相场模型 考虑了晶体表面能、枝晶尖端动力学、最优生长取 向等多种因素, 能够模拟枝晶的形貌细节, 同时许 多学者[8~14]采用相场方法开展了从二元到多元、强制 对流、二维到三维等多种角度模拟枝晶生长过程已 经取得了较好的结果, 但相场法也具有网格尺寸较 小、计算域有限、计算量巨大的特点, 因而不适用较 大尺度计算, 难以实现与宏观凝固条件的耦合模 拟. CA 方法由 Rappaz 和 Gandin[15]首次应用于模拟 晶粒及枝晶组织凝固生长过程, 该方法结合了确定 性方法和随机性方法的特点, 在模拟晶粒组织方面 表现出了明显的优势. CA 方法耦合有限差分法(finite difference, FD)模拟金属凝固的质量守恒及能量 守恒过程, 解决了传质与传热等计算问题; 采用瞬 时形核模型和连续形核模型, 处理定向凝固组织形 核过程, 反映了晶粒取向及位置的随机性特征; 晶
第 50 卷
第3期
2014 年 3 月 第 345-354 页
ACTA METALLURGICA SINICA
Vol.50 No.3 Mar. 2014 pp.345-354
DD6 高温合金定向凝固枝晶生长的数值模拟研究*
张 航 1) 许庆彦 1) 史振学 2) 柳百成 1)
1) 清华大学材料学院先进成形制造教育部重点实验室, 北京 100084 2) 北京航空材料研究院先进高温结构材料重点实验室, 北京 100095
Correspondent: XU Qingyan, professor, Tel: (010)62795482, E-mail: scjxqy@
Supported by National Basic Research Program of China (No.2011CB706801), National Natural Science Foundation of China (No.51171089) and National Science and Technology Major Project (Nos.2011ZX04014-052 and 2012ZX04012-011)
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concerning the HRS method's macro solidification parameters. Mathematic models for dendrite grain growth controlled by temperature field and solute field were built to describe the competitive growth and morphology evolution of dendrite grains. Then the dendrite calculation model was coupled with the models of DS process calculation, and some HRS solidification parameters were included, such as withdrawal rate, pouring temperature, etc. The coupled models were used to predict the dendrite grain competitive growth of DD6 superalloy during the DS process. The variation of solute distribution and the dynamic adjustment of dendritic spacing during the process could be predicted by simulating calculation. The DS experiment was carried out with a cylinder sample, and dendrite grains' distribution in the transverse and longitude section was observed by OM and SEM. Then the simulated dendritic morphology was compared with that by experiment. The primary and secondary dendritic spacing by experiment and simulation were measured, and the compared results revealed that as the DS process going on the temperature gradient decreased gradually and the primary dendritic spacing was increasing. So simulation results of the DS dendritic competitive growth were validated by the experiment results, and the proposed models could predict the dendrite grain morphology and the adjustments of DS dendritic spacing of DD6 superalloy very well.
ZHANG Hang ,1) XU Qingyan ,1) SHI Zhenxue ,2) LIU Baicheng 1)
1) Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, School of Materials Sciences and Engineering, Tsinghua University, Beijing 100084
Manuscript received 2013-08-18, in revised form 2013-11-30
ABSTRACT Modern aero and power industry needs high- performance gas turbine. Directional solidification
中图法分类号 TG132.3
文献标识码 A
文章编号 0412-1961(2014)03-0345-10
NUMERICAL SIMULATION OF DENDRITE GRAIN GROWTH OF DD6 SUPERALLOY DURING DIRECTIONAL SOLIDIFICATION PROCESS
(DS) columnar grain and single crystal (SX) blade as key parts of gas turbine serve in heavy stress and high temperature conditions. The DS and SX blade are mainly produced by high rapid solidification (HRS) method, and HRS is one of useful DS technology, which has a property that the heat dissipating ways are changing during the process and the temperature gradients will vary correspondingly. The dendrite grain arrays were the substructure of a DS or SX blade. The structure of the dendrite grain arrays influences the mechanical property of the final casting very much, but is seriously affected by the solidification parameters, such as temperature gradient. In this work, the dendrite grain growth of DD6 superalloy was studied based on cellular automaton- finite difference (CA- FD) model
高温合金树枝晶的竞争生长及形貌特征, 描述了凝固过程的溶质分布变化及枝晶间距的动态调整过程. 研究工作将模拟结
果与实验结果进行了对比, 两者吻合良好. 模拟能够预测 DD6 高温合金 HRS 法定向凝固过程的枝晶形貌及一、二次枝晶间
距动态调整过.
关键词 元胞自动机, DD6 高温合金, 定向凝固, 枝晶生长, 数值模拟
2) National Key Laboratory of Science and Technology on Advanced High Temperature Structural Materials, Beijing Institute of Aeronautical Materials, Beijing 100095
* 国 家 重 点 基 础 研 究 发 展 计 划 项 目 2011CB706801, 国 家 自 然 科 学 基 金 项 目 51171089 及 国 家 科 技 重 大 专 项 项 目 2011ZX04014- 052 和 2012ZX04012-011 资助 收到初稿日期: 2013-08-18, 收到修改稿日期: 2013-11-30 作者简介: 张 航, 男, 1985 年生, 博士生 DOI: 10.3724/SP.J.1037.2013.00496
摘 要 采用元胞自动机-有限差分(CA-FD)方法对 DD6 高温合金高速凝固法(HRS, high rapid solidification)定向凝固树枝晶
三维生长过程进行模拟研究. 建立温度场和溶质场耦合控制的枝晶生长模型, 考虑抽拉速率和温度梯度等凝固条件的影
响, 同时考虑成分过冷、溶质分配系数、晶体择优取向等合金物性参数, 模拟研究了枝晶形态的演化过程. 模拟结果反映了
KEY WORDS CA, DD6 superalloy, directional solidification, dendrite grain growth, numerical simulation
现代航空工业及能源动力行业对涡轮燃气机 热端部件的性能要求越来越高. 定向柱状晶及单晶 叶片是重要的涡轮发动机热端部件, 其材料及加工 工艺也出现了飞跃式的发展. 国际上先进的单晶高 温合金已经发展至第六代[1,2], 我国的高温合金材料 研发也取得了长足的进步[3,4]. DD6 合金是我国研制 的第二代单晶高温合金[5], 该合金具有成本低、综合 性能优良、铸造工艺性好等特点. 定向凝固枝晶组 织是单晶晶粒的亚结构, 枝晶定向生长的结构特点 决定了叶片优异的单向力学性能. 因而研究枝晶定 向生长特点, 控制其生长形貌及分布特征成为定向 凝固工艺的重要内容. 而枝晶定向生长的影响条件 及本质规律也成为研究的热点[6,7].