Electron microscope study of the effect of deformation on precipitation and recrystallization in copper-titanium alloys

Abstract

Structural changes occurring during aging of deformed as-quenched copper-titanium alloys were studied by means of hardness measurements and thin foil electron microscope examination. It was demonstrated that the average subboundary misorientation tends to increase with increasing strain values. The development and microstructure of deformation bands and their role in precipitation and recrystallization are discussed. Depending on the degree of deformation and aging temperature nucleation of either recrystallized grains or discontinuous precipitates was observed. After deformation lower than 30 pct the formation of recrystallization nuclei proceeds according to the strain induced boundary migration mechanism. After higher deformation recrystallization nuclei are formed mostly within deformation bands. A schematic TTT diagram is proposed, illustrating the sequence of various phase transformations that occur in the alloys investigated. The tendency of TTT curves shifting with increasing deformation, and a range of proposed heat treatment are discussed. It is shown that in deformed alloys spinodal decomposition occurs at aging temperatures lower than those in the underformed ones. Coarsening of modulations is affected by heterogeneous α' and β' phases precipitation, which is followed by discontinuous precipitation of α and β' phases of determined crystallographic relationship.