Soft magnetic amorphous alloys in X-ray light: Insights from ultra-fast Joule heating experiments

In this contribution a novel setup for studying rapid crystallization of metallic glasses using a time resolved in situ X-ray diffraction combined with a direct current fast Joule heating (flash-annealing) is presented. The setup was implemented and successfully tested at the P02.1 beamline of the PETRA III storage ring (DESY Hamburg, Germany). Its potential use is demonstrated by studying rapid crystallization of soft magnetic Fe73.5CU1Nb3Si15.5B7 (at.%) metallic glass prepared by melt spinning technique. Flash-annealing experiment is realized by bursting 20 rectangular current pulses with a fixed amplitude of 1.5 A and pulse length delta is varied (30, 40 and 50 ms). A single pulse with duration of 30 ms causes temperature to rise to 770 degrees C with an average heating rate of 4200 K/ s. Phase composition of crystallized material consist of major Fe3Si phase and small traces of boride phase Fe23B6. Consecutive pulses result in cyclic thermal expansion of a crystal lattice, which appears fully reversible. Increasing pulse width to 50 ms causes temperature to increase up to 1020 degrees C with an average heating rate of 5600 K/s. Differentiation of the temperature profile yields exceptionally high value of heating rate 10800 +/- 2400 K/s.