A neutron small-angle scattering study of the HfPd system

The HfPd system exhibits a fast amorphization reaction. A series of specimens has been prepared by mechanical alloying (MA). X-ray diffraction (XRD) and small angle neutron scattering (SANS) were used to characterise the structural transformations during the amorphization reaction. Contrast-matching technique was used to isolate the powder surface effects and obtain the scattering from the bulk of the specimens. The structural transformations observed by the wide-angle measurements are reflected in the large-scale structure and this was detected by SANS. A strong SANS intensity profile is obtained for the parent specimen relative to those obtained for the MA treated specimens. More interesting is that the SANS intensity profiles for both the amorphous HfPd obtained by MA and that obtained by fast quenching (FQ) are almost identical, indicating similar structure on a large scale. However, the structure of particles within the amorphous phase obtained by MA is of more convoluted surfaces compared to those produced by FQ. Graphs of the log[I(Q)] vs. log(Q) are linear over a wide range of scattering vector Q indicating the fractal nature of the structure in these specimens. The fractal dimensions D were obtained as a function of MA time. (orig.)