Ni-7.3%Si-2.2%B合金快淬组织与深过冷快凝机制

 采用B_2O_3玻璃和纯循环过热净化相结合的方法去除液态金属中的异质晶核,使液态Ni-7.3％Si-2.2％B合金获得了330K的过冷度。对比分析了该合金在低温基板上的快淬薄片与大体积深过冷试样的微观组织。借助计算机和红外测温系统,快速采集了熔体的再辉过程。数据处理发现,在深过冷液态金属的整个再辉区间,温度的上升速率呈瞬态变化特征,再辉时间随初始过冷度的提高而减小。最后,由再辉曲线确定出深过冷液态金属再辉过程中的固相分数与时间以及凝固速度与瞬时过冷度的关系。

MICROSTRUCTURES OF RAPIDLY QUENCHED FOILS AND SOLIDIFICATION MECHANISM OF BULK UNDERCOOLED Ni-7.3%Si-2.2%B ALLOY

The microstructures of rapidly quenched Ni-7.3%Si-2.2%B foils chilled at the copper substrate have been compared with bulk undercooled Ni-7.3%Si-2.2%B alloy. The application of boron oxide fluxing method as well as pure successive heating-cooling cycles treatment enables such investigations over a wide range of undercooling up to ATi = 330K.The high speed data acquisition and processing of cooling cycles of melts are accomplished by a microcomputer(Apple II). It has been shown that (1)recalescence takes place in two stages: first, rapid temperature rise; second, much slower recalescence.(2) Recalescence times for Ni-7.3%Si-2.2%B alloy decrease with increasing the initial undercooling. Finally, in the light of measured recalescence curves both the dependence of the fraction solid on time and the solidification rate on transient undercooling were determined.