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The first successful application of a new method to investigate phase transformations in real time, like the decomposition of austenite into bainite in grey iron, is described. During the ongoing transformation, transmission spectra of thermal neutrons, which contain Bragg edges corresponding to the crystal structure of the transforming phases, are recorded. By evaluating the height of these Bragg edges, which is a measure of the volume fraction of the phase, at different transformation times, the transformation can be followed in-situ in a time resolved manner. The method is compared to other previously used methods (micrographs, dilatometry, diffraction techniques); also a summary and an outlook are given.

Low-energy neutron transmission diffraction has been successfully demonstrated to be a powerful experimental method to investigate changes in crystal structure development down to the millisecond range. Bragg edge diffraction measurements thus can be the basis for future experiments like strain radiography, determination of the strain-rate dependent elastic properties of engineering materials, temporal development of phase changes, structural properties of materials under extreme environmental conditions like high pressure or temperature states. At high instantaneous neutron bursts current-mode detection can be used, which enables both transient and stroboscopic measurements. Progress has been made in rapid data acquisition and analysis as well as temperature measurement by resonance doping.

The neutron intensity transmitted through polycrystalline material exhibits sudden well defined increases whenever the neutron wavelength ceases to fulfil the Bragg coherent scattering condition for a specific subset of lattice planes. Since in the transmitted beam all diffracted neutrons are absent, the so-called Bragg edges build up very rapidly, because diffraction of neutrons into the full solid angle contributes to their presence. High peak-intensity neutron bursts may be detected using the current-mode technique, opening up the possibility to do both transient and stroboscopic measurements. This new method is relevant to different research areas, like transient phase transformation, melting and solidification, dynamic stress influence or materials under extreme environmental conditions. Progress has been made in rapid data acquisition and analysis as well as temperature measurement by resonance doping.