Speaker
Description
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.
