正负温度梯度条件下Al-4.5%Cu合金枝晶组织生长机制对比研究  

Dendrite growth mechanism comparison of Al-4.5%Cu alloy under positive and negative temperature gradients

作　　者：王昕[1] 王建元[1] 翟薇[1] WANG Xin;WANG JianYuan;ZHAI Wei(School of Physical Science and Technology,Northwestern Polytechnical University,Xi’an 710072,China)

机构地区：[1]西北工业大学物理科学与技术学院,西安710072

出　　处：《中国科学:技术科学》2025年第3期475-490,共16页Scientia Sinica(Technologica)

基　　金：国家自然科学基金(批准号:52088101,52130405);国家重点研发计划(编号:2021YFB3502600,2021YFA0716301);陕西省自然科学基础研究计划(编号:2023-JC-JQ-28);陕西省秦创原“科学家+工程师”队伍建设(编号:2022KXJ-177)资助。

摘　　要：采用强制定向凝固和自由快速凝固实验技术,系统研究了Al-4.5%Cu合金在正和负温度梯度下的凝固动力学过程和组织演变规律.正温度梯度条件下,固液界面前沿的冷却速率仅为1.1×10^(-3)~2.3 K·s^(-1),此时组成过冷是主要过冷形式,其数值低于理论结晶温度间隔78 K.负温度梯度条件下,合金液滴冷速随着直径的减小不断升高,相比正温度梯度提高6个数量级以上,同时过冷度显著增大,最大值可达170 K.恒定正温度梯度下,初生α-Al相固液界面形态随生长速度增大发生“平界面—胞晶—枝晶”转变.随着正温度梯度的提高,界面转变临界生长速度不断增大,同时定向生长枝晶的顶端半径缓慢增大,一次枝晶间距和二次枝晶间距逐渐减小,其固相溶质浓度始终低于合金原始成分.负温度梯度作用下,初生α-Al相呈现出单点形核定向生长和多点形核等轴生长两种组织形貌.随着合金液滴直径减小,生长速度和过冷度的提高使得单点形核的α-Al相发生“枝晶—胞枝晶—胞晶”组织转变,而多点形核的等轴枝晶则转变为细小的近球状等轴晶,两者的一次枝晶长度和二次枝晶间距均不断减小.在100 K以上过冷度下,α-Al固相实现了无偏析枝晶生长.The dendritic growth kinetics and microstructural evolution mechanisms of Al-4.5%Cu alloy under positive and negative temperature gradients were explored by constrained directional solidification and free rapid solidification techniques.In the case of the positive temperature gradient,the cooling rate at the solid/liquid interface was only 1.1×10^(–3)~2.3 K/s,while the constitutional supercooling played a dominant role but was below the theoretical freezing temperature interval of 78 K.In the situation of a negative temperature gradient,the cooling rate of alloy droplets increased rapidly with the reduction of their diameters and was elevated by six orders of magnitude if compared with a positive temperature gradient condition.Meanwhile,droplet supercooling also rose remarkably to attain a maximum of 170 K.If a positive temperature gradient was kept constantly the continuous increase of growth velocity resulted in the successive“planar—cellular—dendritic”interface transitions.The growth velocity thresholds for these two structural transitions increased with temperature gradient rise,which was accompanied by the obvious reduction of both primary and secondary dendrite arm spacings ofα-Al phase.But the corresponding dendrite tip radius showed a slowly increasing tendency,and the interfacial solid concentration was below the initial alloy composition.Under the influences of the negative temperature gradient,theα-Al phase exhibited a kind of directionally growing dendrite structure originating from the single nucleation site plus the ordinary equiaxed dendrites formed from multiple nucleation sites.Similar to the directional solidification process,the sufficient increase of growth velocity and liquid supercooling within tiny alloy droplets induced the successive“dendrites—cellular dendrites—cells”structure transitions after single-site nucleation.On the other hand,an abrupt grain refinement effect from equiaxed dendrites into spheroid crystals was initiated in multiply nucleated alloy droplets.On

关 键 词：温度梯度 定向凝固 固液界面 深过冷 快速凝固 枝晶生长 

分 类 号：TG1[金属学及工艺—金属学]