  The study focuses on corrosion fatigue processes taking place in an
ultrafine-grained (UFG) near-a-titanium alloy Ti-2.5Al-2.6Zr (Russian
industrial name PT7M) used in nuclear engineering. UFG structure formed with
Rotary Swaging is found to increase resistance to corrosion fatigue. Parameters
of the Basquin's equation are defined and the slope of the fatigue curve
Sa-lg(N) is shown to depend (nonmonotonic dependence) on the UFG alloy
annealing temperature. This effect can be explained with the patterns of
microstructural evolution in a UFG alloy PT7M during annealing: (1) reduced
density of lattice dislocations, (2) precipitation and dissolution of zirconium
nanoparticles, (3) release of a''-phase particles causing internal stress
fields along interphase (a-a'')-boundaries, and (4) intensive grain growth at
elevated annealing temperatures. It is shown that the fatigue crack closure
effect manifested as changing internal stress fields determined using XRD
method may be observed in UFG titanium alloys.
