宏观偏析“黑斑”形成的Rayleigh判据及应用

对合金宏观偏析(黑斑)研究中出现的各种形式的Rayleigh判据及其应用进行了总结。讨论了各种判据产生的条件及使用范围。根据Flemings的宏观偏析理论建立了一种考虑凝固界面倾角效应的黑斑通用判据,并讨论了该判据在特殊条件下的表达式,找出了它与其它判据的联系。利用垂直向上和水平定向凝固方法试验检验了这些判据的正确性。发现Worster提出的判据和Flemings的宏观偏析理论是一致的。凝固速率对黑斑形成的影响大于温度梯度的影响,考虑凝固界面倾角的判据能更好的预测黑斑的形成。

Rayleigh criteria for freckle formation and their application

Different versions of Rayleigh criteria for freckle formation during the study of macrosegregation were summarized in this paper. The conditions on which they were deduced and the serviceable range of them were discussed .A universal freckle criterion for solidification with a tilted front was found according the macrosegregation theory of Flemings. The expressions of this criterion on some specific conditions were given and the relationship between other criteria and it was found. Experimental verification of the criteria was carried out using the upward and horizontal directional solidification. It was found that the Rayleigh criterion proposed by Worster was consistent with the macrosegregation theory of Flemings. Dendrite growth rate was found to be a more important factor affecting the freckle formation than thermal gradient. The criteria taking into account tilted angle of the solidification front could more accurately predict the occurrence of freckle.