Abstract: 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.

Key words: rapid quenching, bulk undercooling, recalescence curves, data acquisition and processing