Time-resolved X-ray scattering studies of rapid crystallization of amorphous metals

Abstract

Time-resolved X-ray scattering has been used to study the kinetics of crystallization of amorphous metals on time scales varying from minutes to milliseconds. Measurements have been at the National Synchrotron Light Source, using a wide-bandpass monochomator and fast linear position-sensitive detector system at the IBM/MIT beamline X-20C. With this apparatus, scattering patterns from the transforming material can be acquired with 3-ms time resolution. A fast pyrometric temperature controller has been developed to change and regulate the sample temperature with microsecond response. In a typical measurement, two synchronized position-sensitive detectors provide complementary in situ information about the transformation. The first is used for wide-angle scattering and allows us to determine which phases are present and to what extent. Changes in lattice parameter and particle size can also be deduced. The second detector measures small-angle scattering, yielding additional information about the microstructure, such as the spacing between lammellae in eutectic systems. At relatively slow transformation rates, quantitative measurements of crystal volume fractions as small as 10-4 are possible. In many systems, as the transformation rate is increased, the crystallization mechanism changes such that new metastable crystal phases are formed en route to the equilibrium structure. © 1993 Plenum Publishing Corporation.