深过冷Ni-32.5%Sn共晶合金凝固过程中的再辉与组织形态

 采用高温过热法去除异质晶核,使15g液体Ni-32.5％Sn共晶合金过冷度达395K(0.28T_E),借助快速红外测温技术研究了再辉现象及其与过冷、晶体形核和长大、以及凝固组织的关系,并对再辉过程中的结晶分数进行了近似计算。

RECALESCENCE BEHAVIOUR AND SOLIDIFICATION STRUCTURE OF HIGHLY UNDERCOOLED Ni-32.5%Sn EUTECTIC ALLOY

Large undercoolings up to 395K(0.28TE)have been obtained for Ni-32.5% Sn eutectic alloy by superheating the alloy melt which is 15g in weight to 108-976K above its eutectic temperature and consequently destroying a considerable number of heterogeneous nuclei within it. The recalescence phenomenon, its dependence on undercooling and crystal nucleation and growth, as well as its relationship to solidification structures have been studied. The crystallization fraction during recalescence is also calculated. It is found that the degree of recalescence increases with undercooling when the latter is below a certain critical value ATc, but it decreases as undercooling increases above ATc (in the specific case of the present paper, △Tc = 245K, i. e. 0.17TE).The greater the degree of recalescence, the larger the proportion of anomalous eutectic in the solidified structures. If the degree of recalescence is quite small, it is impossible for the anomalous eutectic to become the only solidification structure, and a certain a-mount of lamellar eutectic inevitably forms even at undercoolings as large as 376K.