摘要
采用低网格各向异性元胞自动机(cellular automaton,CA)模型研究了激光重熔条件下的反常共晶生长机制。为了验证模型的可靠性,建立了二维层片规则共晶CA模型,针对CBr4-C2Cl6共晶合金,模拟了1l O失稳形态向2l O失稳形态转变过程,计算结果与实验、相场模拟结果吻合。模型通过设定含三相(a、b和液相)的界面元胞,使CA模型中a和b相体积分数能够连续变化,从而更易于捕捉二维层片共晶的失稳过程。与相场模拟结果相比,本工作计算得到1l O-2l O失稳形态,即1l O和2l O失稳的中间状态,并与实验结果吻合。在上述二元共晶CA模型基础上,对Ni-Sn合金粉末床激光重熔条件下,熔池底部出现的从规则层片状向非规则反常共晶组织的转变过程进行模拟研究,发现在初始低冷却速率条件下,细小的层片共晶发生失稳,即b-Ni3Sn相超越a-Ni相,形成b-Ni3Sn单相定向生长,在后续加速冷却过程中,固/液界面前沿液相中a-Ni相形核,并发生b-Ni3Sn相包裹a-Ni相生长形成反常共晶组织。激光重熔过程中,由熔池底部到顶部的凝固过程中确实存在一个由凝固速率为零到接近扫描速率的快速变化过程,因此与CA模拟采用的变抽拉速率的凝固条件吻合。
Eutectic is one of the most commonly observed solidification patterns, the growth morphology of which is important to materials properties. Anomalous eutectic is typically coarser and globular than lamellar eutectic, which is commonly observed during solidification of binary eutectic alloy, including deep undercooled melt and laser remelting process. The morphological evolution mechanism of anomalous growth is still unknown due to the lack of simulation evidence. During laser remelting process, the anomalous eutectic is sandwiched between lamellar eutectic at the bottom of melt pool. Comparing to deep undercooled melt, laser remelting has simpler temperature field distribution, which can be simplified into directional solidification. Thus, simulations of anomalous eutectic growth in laser remelting process are feasible. In the present work, the anomalous eutectic growth mechanism under laser remelting conditions was simulated using a low mesh induced anisotropy cellular automaton(CA) model. Firstly, a twodimensional lamellar eutectic CA model of CBr4-C2 Cl6 alloy was established, and the morphological transition from 1 l O to 2 l O was simulated. The calculated results are in good agreement with experiments and phase field simulations. By setting the interface cells containing three phases(a, b and liquid phases),the model can continuously change the a and b phase volume fractions in the CA model, making it easier for the model to capture the instability of lamellar eutectic. Compared with the results of the phase field model, the intermediate 1 l O-2 l O state of oscillation instability of 1 l O and 2 l O which is consistent with the experimental results was calculated. Based on the above-mentioned binary eutectic CA model, the lamellar eutectic to anomalous eutectic transition at the bottom of the molten pool was simulated. Under the condition of initial low cooling rate, the fine lamellar eutectic is decoupled, it leads to the overgrowth of b-Ni3 Sn phase. During the subsequent accelerated cooling process, a-N
作者
魏雷
曹永青
杨海欧
林鑫
王猛
黄卫东
WEI Le;CAO Yongqing;YANG Haiou;LIN Xin;WANG Meng;HUANG Weidong(State Key Laboratory of Solidification Processing,Northwestern Polytechnical University,Xi'an 710072,China;Key Laboratory of Metal High Performance Additive Manufacturing and Innovative Design,Ministry of Industry and Information Technology,Northwestern Polytechnical University,Xi'an 710072,China;School of Materials Science and Engineering,Luoyang Institute of Science and Technology,Luoyang 471000,China)
出处
《金属学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第12期1801-1808,共8页
Acta Metallurgica Sinica
基金
国家重点研发计划项目No.2016YFB1100100
国家自然科学基金项目Nos.51604227
51323008
51475380和51271213
国家重点基础研究发展计划项目No.2011CB610402
国家高技术研究发展计划项目No.2013AA031103
西北工业大学凝固技术国家重点实验室自主研究课题项目No.128-QP-2015~~
关键词
反常共晶
数值模拟
元胞自动机
anomalous eutectic
numerical simulation
cellular automaton
