Compared with crystalline counterparts,
metallic glasses (MGs) have some superior properties, such as high yield
strength, hardness, large elastic limit, high fracture toughness and corrosion
resistance, and hence are considered as promising engineering materials. Fe-
and Co-based amorphous alloys have been the subject of considerable research
interest and activities for the last decades due to applications related to
their outstanding soft magnetic properties. Structurally, metallic glasses can
be classified as disordered materials. X-ray diffraction (XRD) using
high-energy photons has proven to be well suited for describing the structure
of highly disordered systems such as MGs.
Time-resolved in situ XRD experiments may nowadays be performed at high-brilliance
synchrotron radiation sources for a variety of conditions which help to
elucidate the structure–property relations.
In this
contribution structural changes occurring in an Fe72.5Cu1Nb2Mo2Si15.5B7
alloy during a combination of constant rate heating (20 K/min) and isothermal
holding at 500 and 520 C will be investigated using in situ high-energy X-ray
diffraction. It was found that the ferromagnetic-to-paramagnetic transition of
the amorphous phase is revealed as a change in the slope of the thermal
expansion curve when heating a sample at a constant rate up to 520 C. Real
space analysis by means of the atomic pair distribution function (PDF)
demonstrated that the rate and extent of the thermal expansion strongly depend
on the interatomic separation. The PDF proved to be a reliable method for the
description of crystallization kinetics. Further it allows determination of
sizes of ultrafine nanocrystals with grain sizes well below 8 nm and thus makes
observation of early stages of nanocrystallization
possible. This contribution presents results showing how pair distribution function
can be successfully used for tracking the ferromagnetic-to-paramagnetic
transition of amorphous phase in the vicinity of the Curie point.