NON-DESTRUCTIVE IN-SITU REAL-TIME MEASUREMENTS OF STRUCTURAL PHASE TRANSITIONS USING NEUTRON TRANSMISSION, S. Vogel, H.-G. Priesmeyer, M. Bourke, E. Ustundag, J.C. Hanan, pp. 75-84

In recent years, a novel technique has been developed to study the kinetics of structural phase transitions in solids. The method is based on the Bragg-edge phenomenon associated with the transmission of thermal neutrons through a material. In a transmitted spectrum the neutrons that have interacted with the sample are missing, and it is possible to derive information concerning the structure of the sample. Such a Bragg-edge transmission spectrum is, in a sense an inverse diffraction pattern. Because of the high intensity available at modern pulsed neutron sources and the large number of neutrons transmitted by a typical sample system, a spectrum of sufficient statistics can be acquired within few minutes or even much less than a minute. Therefore, Bragg-edge temporal resolution is closer to synchrotron temporal resolution than conventional neutron diffraction and has the characteristic penetration in high Z systems associated with neutrons. The data analysis of such patterns is not compatible with analysis software for diffraction patterns. In the latter field, the Rietveld approach has been established as a quasi standard and proved to be very valuable. Consequently, a Rietveld-style code has been developed for transmission data, allowing one to extract crystallographic information (volume fractions, lattice parameters, texture) by analysing the full pattern. The current state of this development is presented. Examples are presented including measurements of the austenite to bainite transition at various temperatures in Si-rich steel, and measurements of the reduction of nickel oxide to nickel at 1100◦C.