Transmission energy dispersive X-ray diffraction as a tool for the laboratory study of fast processes in metals

In this work, an in-situ study of phase transitions in low-carbon steel is presented. The phase changes were monitored by the transmission energy dispersive X-ray diffraction technique during the heating, annealing and quenching cycle of the sample under standard laboratory conditions. During energy dispersive X-ray diffraction, the sample volume was transmitted with a pencil beam generated by a standard polychromatic X-ray tube without any spectral filtering. Two-dimensional polychromatic diffraction images were acquired by a Timepix 3 pixelated detector. This detector is capable of achieving a throughput of up to 38 Mhits/s in continuous stream mode using USB 3.0 interface. For each detected photon, its position is known with an accuracy of 55 µm in the detector plane and its energy with a resolution of 4 keV at 60 keV. The recorded polychromatic data is then recomputed to get the equivalent monochromatic XRD pattern that would be produced using a monochromatic X-ray source. Thanks to the 90 kV voltage potential of the X-ray tube, the polychromatic pencil beam was able to pass through a highly attenuating sample made of 1.5 thick steel sheet. In addition, by utilizing the entire X-ray spectrum, the pencil beam has a sufficiently high brilliance to obtain XRD patterns rapidly enough to investigate relatively fast processes with temporal resolution of 10 s. It made to possible to analyze the phase transitions in a polycrystalline sample during its temperature treatment under standard laboratory conditions.