切向流动对偏晶合金定向生长机理的影响

研究了静态和切向流动作用下对二氯苯-丁二腈(DCB-SCN)偏晶合金的定向凝固过程.实验结果表明,静态条件下,DCB以小平面相方式生长,随着抽拉速度的提高,DCB-SCN偏晶凝固组织形貌发生液/固两相完全分离组织-规则纤维状共生组织-不规则弥散组织转变.施加切向流动作用后,DCB生长晶面出现胞状扰动,并且偏晶共生纤维间距随流速的增高而变大,但对于同一流速,仍然满足λV^0.5=常数.同时,切向流动能够细化弥散偏晶组织中第二相颗粒尺寸,这主要缘于流动引发的固液界面形态变化能

Directional growth of monotectic alloy with and without shear flow

The directional growth process of para-dichlorobenzene and succinonitrile (DCB-SCN) monotectic alloy is realized under static condition and in presence of shear flow. The experimental results show that, with the increase of pulling rate, the DCB phase exhibits faceted growth while the monotectic structure undergoes a transition in which "separated liquid and solid phases-aligned fibrous composite structure-droplet dispersion in solid matrix" take place. When shear flow is applied, perturbation and fluctuation appear at each growing crystal plane. In the meantime, the fibrous spacing is larger compared with those under the same pulling rate without flow. However, the spacing and pulling rate also follow the relationship λV^0.5=C. In the formation process of droplet dispersion structure, shear flow enhances the nucleation rate of second liquid drops and hinder the growth and interaction of second liquid droplets at the solid-liquid interface, leading to the refinement of the final droplet dispersion structure.