A new approach to the study of the α–σ phase transformation

It is demonstrated that the kinetics of the α-σ phase transformation in the Fe-Cr based alloys can be studied from the average isomer shift. Using this new approach it is shown that the size of grains significantly affects the formation of the σ-phase, while that of the α-phase does not depend on the microstructure. This revised version was published online in August 2006 with corrections to the Cover Date.     

How do atoms jump in ordered alloys? the model system Fe−Al

Summary Our aim is to reveal the elementary diffusion jump of Fe atoms in ordered Fe−Al single crystals (Fe contents 50.5, 55, 66 and 75 at.%) by comparing results from quasi-elastic M?ssbauer spectroscopy at⁵⁷Fe with results from other methods. The mechanism obviously follows one and the same logics irrespective of the alloy composition: Fe atoms jump into second or third nearest-neighbour sites on their own sublattice via the lying-between antistructure site on the Al sublattice. Since the disorder increases with increasing Fe concentration, the residence time of Fe atoms on the antistructure sites increases at the same time. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Vibrational properties of nanograins and interfaces in nanocrystalline materials

The vibrational dynamics of nanocrystalline Fe(90)Zr(7)B(3) was studied at various phases of crystallization. The density of phonon states (DOS) of the nanograins was separated from that of the interfaces for a wide range of grain sizes and interface thicknesses. The DOS of the nanograins does not vary with their size and down to 2 nm grains still closely resembles that of the bulk. The anomalous enhancement of the phonon states at low and high energies originates from the DOS of the interfaces and scales linearly to their atomic fraction.     

Time-domain interferometry using synchrotron radiation applied to diffusion in ordered alloys

Time-domain interferometry of synchrotron radiation (TDI) has recently been used as a tool for investigating diffusion in glasses. This work deals with an extension of this technique to ordered structures. In a TDI experiment performed on the B2 alloy CoGa at the APS the intensity scattered into Bragg directions showed no detectable quasielastic signal. Experimental lower limits of the elastic contribution are given. They are in accordance with the coherent scattering function derived in this paper. This result indicates that TDI can be applied to diffusion in crystalline solids, e.g. intermetallic alloys, by using diffuse scattering. Requirements and limitations of diffuse scattering experiments are discussed. Received 21 September 2000 and Received in final form 13 December 2000     

Diffusion Studies with Synchrotron Radiation and with Neutron Scattering

With scattering methods we are able to detect the elementary diffusion jump. This is a report on investigations with methods working in the time domain, i.e., nuclear resonant scattering of synchrotron radiation and neutron spin echo. The accent of this paper is on diffusion in ordered alloys. We finish with an outlook on what will be possible with the upcoming potential of future synchrotron sources. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diffusion in crystalline materials

Recently nuclear scattering of synchrotron radiation proved to be a powerful new method to study the elementary diffusion jump in crystalline solids. The scattered radiation decays faster when atoms move on the time scale of the excited-state lifetime of a Mössbauer isotope because of a loss of coherence. The acceleration of the decay rate differs for different crystal orientations relative to the beam providing information not only about the rates but also about the directions of the elementary jumps. We discuss first applications of the method.