Strain-Induced and 'Electrochemical' Interactions of #beta#-Stabilising Substitutional Atoms in H.C.P.-Titanium Alloys

摘要

An instability with respect to the phase transformations in h.c.p. -Ti alloys with isomorphous (Mo, Ta, Nb) and eutectoid (Fe, Cr) #beta#-stabilising elements is studied by analysis of the strain-induced and 'electrochemical' interatomic interactions of substitutional impurity atoms. The method of static concentra-tion waves is used to describe impurity subsystem distribution. Dependencies of the 'mixing'-energies Fourier-components' matrix eigenvalues along 12 main directions within the Brillouin zone are obtained. Analysis of these dependencies had shown that the alloys under consideration are unstable, and an atomic ordering with formation of antiphase isostructure domains is expected; besides, bulk modulations in substitutional atom distribution for these systems must occur within the basal plane, but along the corresponding directions. It has been found that the strain-induced contribution to the impurity-impurity interaction energy in a-fl has a remarkable value and is about 0.1-0.5 eV/atom in magnitude. If the strain-induced interaction is considered only (which would be acceptable for the latest stages of decomposition), the h.c.p. solution should be unstable too, and the character of the phase transforma-tions should be distinct. Isomorphous systems would be tend to spinodal decomposition, and layered atomic ordering along the hexagonal axis would oc-cur in eutectoid systems.