摘要
在凝固过程中，液固界面形态经历了从平面向胞状进而树枝晶，然后又向针状胞直至绝对稳定平界面的演绎过程．本文以理论分析与实验结果为基础，讨论了液固界面稳定性与界面形态的关系和生长速率的影响，阐明亚快凝固段快束生长形成的超细柱晶组织特性及其应用前景．
During solid / liquid phase transformation in solidification process a great variety of interface morphologies can form, such as plane front, cells, dendrites, needle-like cells and new plane front with absolute stability. In this paper, the basic solidification parameters affected the solid / liquid transformation are analysed with an emphasis on the effect of growth velocity on the interface morphologies, and an effective criterion of constitutional supercooling has been presented. As V<V(tr), with the increase of growth velocity the effective constitutional supercooling will be increased, that leads to an decrease of interface stability. Conversly, the effective constitutional supercooling will be decreased and the interface stability increased correspondingly.An in-situ observation and experimental results about the transition of dendrites to needle-like cells by employing a directional solidification furnace with a super-high temperature gradient at high growth velocity is demonstrated. The dynamic pictures of crystal growth of CBr4 during transition from dendrites to cells show that the instability of dendrites begin to appear just at the tip region of crystals in form of splitting, and then the primary dendritic spacing can be adjusted. The experiments also show that directionally solidified superfine sidebranch-free columnar crystals with considerably improved mechanical properties at high temperature can be obtained by using of directionals solidification technology with super-high temperature gradient. Moreover, a space-time limited conditions for transition of dendrites to cells has been discussed and a criterion characterizing the sidebranch-free crystal growth is presented. Finally, the application of superfine structure obtained by using of dendrite to cells transition in nickel-base, cobalt-base and aluminium alloys has also been introduced, the results show that the structure with superfine sidebranch-free columnar crystals has very low segregation and superior mechanical properties in comparision with conventional directionally solidified structures.
出处
《材料研究学报》
EI
CAS
CSCD
1994年第3期209-217,共9页
Chinese Journal of Materials Research
基金
国家自然科学基金
关键词
界面稳定性
金属学
相变
液体
固体
microstructure selection,interface stability,growth rate,superfine columnar crystals
