单晶高温合金固液界面形状及对凝固组织的影响

ＤＤ８单晶高温合金在高温度梯度宽变速定向凝固装置上进行了单晶定向凝固实验，并在实验基础上系统地分析了凝固条件对固液界面形状及凝固组织缺陷的影响。结果表明，提高冷却速率，限制凝固速率在特定临界速率Ｖ＊以下，可以保持平直的固液界面；当超过这一临界速率Ｖ＊时，固液界面出现下凹，下凹的间液界面将导致形成小角度晶界、显微组织疏松及发散凝固组织，高凝固速率将导致定向凝固过程的个稳定性，制造冷却速率的定向凝固装置是实现快速定向凝固的必要条件。

SOLID-LIQUID INTERFACE SHAPE AND MORPHOLO-GICAL DEFECTS OF SINGLE CRYSTAL SUPERALLOY

A series of SC superalloy DD8 samples were directionally solidified in a furnace with high thermal gra-dient and wide velocity scope. And the effects of solidified velocities on the S/L interfacial shape and themorphological defects were gualitatively measured and systematically discussed. The results indicate that aflat S/L interface can be obtained at high cooling rates and low solidified velocities(below critical velocityV*),but concave S/L interface will occur above the V* . The concave interface will lead to the forrnationof low angle boundaries, subgrains, splaying and shrinkage. And the deeper concave interface at high so-lidified velocity will lead to unstable directional solidified processing.