Spinodal decomposition,ordering,and discontinuous precipitation in deformed and aged copper-titanium alloys

Abstract

Phase transformations in quenched, deformed, and aged copper-titanium alloys containing up to 5,6 at.-% Ti were studied by means of hardness measurements and electron microscope examinations of thin foils. The modulation wavelength showed a linear relationship with the logarithm of the aging time. Deformation caused a slower increase of the modulation wavelength and a reduction of the critical spinodal temperature Te. The formation of the Dla superlattice was observed in the titanium-rich modulations. The spatial distribution of modulations is discussed in terms of the ordered domain shape. The formation of an ordered structure is not observed in highly deformed specimens in which heterogeneous precipitation of the transition tetragonal a’ or stable β′ phases occurs on dislocations and other structural defects. The nucleation of discontinuous precipitation occurs in deformed alloys not only at grain boundaries but also at deformation bands and highly misoriented subgrain boundaries. The increased number of nucleation sites affects the kinetics of discontinuous decomposition. Depending on the degree of deformation and aging temperature the nucleation of recrystallization, or discontinuous precipitation, was observed. The mechanisms of recrystallization are discussed.