较低剪切速率下过冷熔体非枝晶组织的形成与演化

来源期刊：金属学报2011年第4期

论文作者：赵力宁 林鑫 黄卫东

文章页码：403 - 409

关键词：半固态； 球晶； 枝晶； 玫瑰晶； 形态稳定性

Key words：semisolid； globular crystal； dendritic crystal； rosette crystal； morphological stability

摘    要：采用SCN-5H₂O(摩尔分数,%)透明模型合金研究了较低剪切速率范围内过冷合金熔体中晶体的生长与演化行为.结果表明,在较大过冷度下,存在一个剪切速率阈值,当熔体剪切速率高于阈值,晶体能够以球状形态生长;当剪切速率低于阈值,晶体以枝晶形态生长.在较低剪切速率下,过冷度较大时,球晶失稳后呈枝晶形态,过冷度较小时,球晶失稳后呈玫瑰晶形态.球晶失稳形成玫瑰晶是由球晶界面扰动胞低速生长过程中尖端发生持续分叉所造成的.

Abstract: With the development of the semisolid metal processing technology,many efforts have been made to understand the relationship of the microstructural evolution with the shear rate and the melt undercooling.The globular and rosette microstructures can be obtained under the different shearing rates and melt undercooling.Since the microstructure evolves rapidly under the general high shearing rate in the previous researches,it is difficult to reveal the formation process of semisolid microstructure in detail.In this work,the evolutions of globular and rosette crystals were studies by using a transparent organic alloy Succinonitrile-5%H₂O (molar fraction) with a small shearing rate. It is found that there is a critical value of the shearing rate in the semisolid process above which the morphology of the globular crystal could be stable and below which it would be destabilized to form equiaxed dendrite.In addition,when the interface lost the stability,the globular crystals will evolve to dendrite under a higher melt undercooling and to rosette under a lower undercooling.The continuous splitting of the tip of the perturbation cells in the globular crystal induces the formation of the rosette morphology.