超声场中气泡稳态空化对枝晶生长过程的作用机制  

Mechanism of effect of stable cavitation on dendrite growth in ultrasonic field

作　　者：张颖[1] 吴文华 王建元[1] 翟薇[1] Zhang Ying;Wu Wen-Hua;Wang Jian-Yuan;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：《物理学报》2022年第24期255-264,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:52088101,51922089,52130405,51727803);陕西省自然科学基础研究计划(批准号:2021JCW-09);陕西省重点研发计划重点产业链项目(批准号:2020ZDLGY13-03)资助的课题。

摘　　要：利用高速摄影技术,实时记录了功率超声作用下succinonitrile-8.3%Water(摩尔分数为8.3%)溶液凝固过程中稳态空化气泡与枝晶间的相互作用,并结合数值模拟揭示了稳态空化对枝晶生长的影响机制.结果表明,稳态空化能够加速枝晶生长、促使枝晶臂断裂和吸附球状晶生长.当气泡的迁移方向与枝晶生长方向一致时,气泡振荡过程中产生的周期性高压导致周围熔体过冷,从而加速枝晶生长.当稳态空化气泡向固相内部迁移时,其振荡引发枝晶臂内部产生大于屈服强度的应力,促使枝晶臂变形和断裂.同时悬浮于固-液界面前沿的稳态空化气泡能够在周围液相中产生局部的周期性变化流场和高剪切力,使得邻近的枝晶碎片将吸附在其周围并以球状晶形态生长.Ultrasonic waves used in liquid alloys can produce refined grain structures,which mainly contributes to ultrasonic cavitation and acoustic streaming.According to the bubble lifetime and whether they are fragmented into“daughter”bubbles,acoustic cavitation can be divided into transient cavitation and stable cavitation.Compared with the transient cavitation,the interaction between stable cavitation bubbles and solidifying alloys have been rarely investigated previously.In this work,the effect of stable cavitation on the dendritic growth of succinonitrile(SCN)-8.3%(mole fraction)water organic transparent alloy is systematically investigated by highspeed digital image technique and numerical simulation.It is found that when the bubble migration direction is consistent with that of dendritic growth,the periodic high pressure generated in bubble oscillation process increases the local undercooling,speeding up the dendrites growth effectively.Meanwhile,the concentrated stress inside dendrites induced by the linearly oscillation of cavitation bubble can break up dendrites into fragments.Specifically,if there exist stable cavitation bubbles suspended around the liquid-solid interface,periodically alternating flow field and high shear force in their surrounding liquid phase is produced.As a result,the nearby dendritic fragments will be attracted to those bubbles and then transformed into spherical grains.

关 键 词：功率超声 稳态空化 枝晶生长 压力过冷 

分 类 号：TG111.4[金属学及工艺—物理冶金]