过冷DD3单晶高温合金凝固组织细化的再结晶机制

RECRYSTALLIZATION MECHANISM FOR THE GRAIN REFINEMENT IN UNDERCOOLED DD3 SINGLE CRVSTAL SUPERALLOY

用复合熔盐净化与循环过热相结合的方法，在 ０—２１０Ｋ过冷度范围内，研究了ＤＤ３单晶高温合金凝固组织形态演化过程．当过冷度△Ｔ超过△Ｔ５（１５３Ｋ）时，枝晶组织开始发生变形、碎断；当△Ｔ超过△Ｔ（１８０ Ｋ）时，组织完全转变为第二类粒状晶．粒化过程中位错及其它晶体缺陷的形态演变表明，△Ｔ以上的晶粒细化是由再结晶机制控制的。

The microstructure evolution of DD3 single crystal superalloy undercooled to 210 K is systematically investigated by employing compound molten salt purification combined with the thermal cycle in high vacuum. When undercooling is beyond 153 K, the dendrite distortion and disintegration take place, and then a kind of complete quasi-spherical equiaxed crystal structure is obtained as the critical undercooling DeltaT* (180 K) is reached. In connection with the observation in the behavior of the crystalline defects, such as dislocation, during the refinement process, it is consequently concluded that the grain refinement above the critical undercooling can be attributed to the recrystallization mechanism.