TIME-RESOLVED X-RAY-DIFFRACTION STUDIES OF CRYSTALLIZATION IN METALLIC GLASSES

Using the new synchrotron X-ray sources. time-resolved X-ray diffraction measurements can be made with millisecond time resolution. In conjunction with a fast pyrometric temperature controller which has been developed to change and regulate the sample temperature with microsecond response, in situ studies of the kinetics of crystallization of metallic glasses on time scales varying from minutes to milliseconds have been made. In a typical measurement. two synchronized position-sensitive detectors provide complementary 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 sometimes particle size can also be deduced. The second detector measures small-angle scattering, yielding additional information about the microstructure, such as the spacing between lamellae in eutectic systems. At relatively slow transformation rates, quantitative measurements of crystal volume fractions as small as 10(-4) are possible. Rapid cooling of the sample at the appropriate time can quench in these transient structures for further electron microscopy studies.