Papers by Keyword: B2 Ordered Phase

Abstract: The results of the analysis of phase equilibria ordered phases in binary systems based on palladium Pd-Me (Me = Co, Rh, Ir, Cu, Ag, Au, Ni, Pt) are set out to search for correlations and crystal-chemical and crystal geometric factors. It is found that the packing factor in disordered solid solutions in binary systems based on Pd is close to the value of 0.74 on a background of a slight deviation from the atomic volumes Xena. It is revealed that increasing of the hydrogen permeability in Cu-Pd binary alloys correlates with significant reduction of the packing factor in B2 ordered phase in the range of 40 at.% Pd. It is found that various structural-phase states are formed in Pd-Me binary systems with certain combinations of temperature and size factors.

Abstract: We have been studying the microstructure change of B2 cubic precipitates into an A2+B2 complex structure in Fe-Al-Ni alloy. In this study, we carried out detailed observation using focused ion beam (FIB) and scanning transmission electron microscopy (STEM). First, Fe-14.3at%Al-10.3at%Ni solid solution was prepared. Secondly, the specimens were heated at 1173 K, at which they formed B2 cubic precipitates (ordered bcc) dispersed in an A2 matrix (disordered bcc). After that, the B2/A2 two-phase specimen was annealed at 973 K. Then we fabricated STEM specimens using FIB, followed by high-resolution secondary electron imaging. We repeated this slice-and-observation procedure to determine the detailed microstructure of this heat-treated alloy. At the early stage of the 973 K annealing, the A2 phase appeared in the original B2 precipitates and showed a spongelike structure, whereas small nanometer-order B2 particles appeared in the A2 matrix. The A2/B2 interface at this stage showed no anisotropic morphology. Therefore, the main driving force of this process may not be strain energy, but chemical and interface energies. Further annealing at 973 K decreased the number of small B2 particles in the A2 matrix, and these particles dissolved into the matrix eventually. The annealing also changed the A2/B2 spongelike structure, which was observed in the original B2 precipitates, into simple structures such as the A2 core and B2 crust. Then the B2 phase showed ordinal coarsening behavior. When B2 precipitates, which had hollow cubic morphology, were observed to be very close to each other, the face-centered area of the B2 crust tended to dissolve and only large B2 precipitates remained.