摘要
采用高温端上升式Bridgman定向凝固实验技术,在0.1~100μm/s跨三量级宽速域生长条件下,系统研究亚共晶Al-4.5%Si合金的组织形态演变机制,实现从平面晶到胞晶再到枝晶的全过程组织调控。当液相温度梯度保持200 K/cm恒定时,发现固液界面失稳的临界生长速度为0.43μm/s,而发生胞枝晶转变的生长速度阈值是3.3μm/s。理论计算揭示出组成过冷(Composition supercooling,CS)区分布范围是2.6~10mm,相应的最大过冷度为2~193.8 K,而实际糊状区长度在2.8~6.2 mm区间变化。实验结果表明,定向枝晶生长模型Kurz-Giovanola-Trivedi(KGT)能够合理预测初生α(Al)枝晶顶端半径、顶端温度和顶端成分,而Hunt一次枝晶间距模型和Kurz-Fisher二次分枝间距模型均与实测结果相一致。初生α(Al)枝晶间的(α(Al)+Si)共晶生长机制定性地符合Jackson-Hunt(JH)经典共晶生长理论。
Liquid hypoeutectic Al-4.5%Si alloy was directionally solidified with a novel Bridgman type apparatus which was featured by the upward motion of heating furnace.A broad growth velocity range covering three orders of magnitude from 0.1μm/s up to 100μm/s was applied to realize the whole structural evolution process from planar interface through cellular morphology until dendritic growth.In order to explore the dominant influences of growth velocity,the liquid temperature gradient ahead of solid/liquid interface was maintained at the constant level of 200 K/cm during all experiments,which shows that the critical growth velocity to initiate S/L interface instability is 0.43μm/s,whereas the growth velocity threshold to induce cell-dendrite transition is 3.3μm/s.The theoretical calculation that the constitutionally supercooled zone extends at 2.6-10 mm in front of S/L interface,where the maximum supercooling varies in the range of 2-193.8 K.In contrast,the actual mushy zone length during directional dendrite growth is in the range of 2.8-6.2 mm.The experimental results validate the theoretical predictions of KGT columnar dendrite growth model for essential parameters as dendrite tip radius,tip temperature and tip compositions.Both the Hunt model for primary dendrite spacing and the Kurz-Fisher model for secondary arm spacing agree well with actual experiments.Nevertheless,the(α(Al)+Si)eutectic growth kinetics within interdendritic spaces of mushy zone only exhibits qualitative consistency with experimental data.
作者
王昕
王建元
翟薇
WANG Xin;WANG Jianyuan;ZHAI Wei(School of Physical Science and Technology,Northwestern Polytechnical University,Xi’an 710072,China)
出处
《中国有色金属学报》
EI
CAS
CSCD
北大核心
2024年第6期1938-1951,共14页
The Chinese Journal of Nonferrous Metals
基金
国家自然科学基金资助项目(52088101,52130405)
国家重点研发计划资助项目(2021YFB3502600,2021YFA0716301)
陕西省自然科学基金资助项目(2021JCW-09,2023-JC-JQ-28)
陕西省秦创原“科学家+工程师”队伍建设基金资助项目(2022KXJ-177)
陕西省重点研发计划重点项目(2020ZDLGY13-03)
关键词
枝晶生长
共晶生长
定向凝固
固液界面
显微组织调控
dendritic growth
eutectic growth
directional solidification
solid-liquid interface
microstructure modulation
