Low-stability pre-transitional states, orderdisorder phase transitions, and B2–A1 structure transformations in the Cu – 40 at.% Pd alloys

Abstract

Low-stability states and peculiarities of structural changes in the region of phase transitions are investigated using the Cu–Pd ~40 at.% Pd alloys as an example. To this end, the crystal lattice and long-range atomic order parameters and the Debye-Waller factors were determined in situ directly in the temperature range of the B2–A1 phases and the order – disorder phase transition using X-ray structural analysis. Based on the data obtained, peculiarities of the B2 and A1 phases in the CuPd alloys were analyzed near the structure-phase transitions and the behavior pattern of atomic vibrations in the crystal lattice was discussed. It is shown that in the CuPd alloys with ~40 at.% Pd, low-stability states are observed, which exhibit a number of anomalous phenomena (such as anisotropy of atomic displacements, splitting, heterophase fluctuations, nonlinearity of the lattice parameter and long-range order parameter dependences, etc.), which precede transformation of the alloy.