Effects of plastic deformation on lamellar structure formation in Ti-39 at.% Al single crystals

The effects of plastic deformation on lamellar structure formation in solution-treated Ti-39 at.% Al single crystals were investigated, focusing on the role of dislocations of different slip systems. The dislocations were introduced by indentation on the surfaces of solution-treated single crystals with different crystallographic orientations. Traces of basal and prism slips were observed, depending on the position relative to the indentation. During annealing at α₂ + γ dual-phase temperatures, lamellar structures were formed faster where basal slip had occurred than where prism slip had occurred. After long annealing, the length scale of lamellar structures formed depends on the slip system operated during prior deformation: in the region where only one of either basal or prism slip had occurred the lamellar structure was coarser than in undeformed crystal, while in the region where both basal and prism slips occurred the lamellar structure was finer than those formed in undeformed crystal. The reasons for the differences in lamellar structures are discussed on the basis of the frequencies of stacking fault formation on (0 0 0 1) planes as precursors to γ-precipitates. The results suggest that the cross-slip of dislocations between basal and prism planes, which gives rise to the formation of multiple stacking faults on many parallel (0 0 0 1) planes, is responsible for the refinement of lamellar structures.