The effect of disordered γ precipitates on the cyclic deformation behavior of γ’-Ni3(Al,Ti)-based single crystals with a L12 structure was investigated. The γ precipitates, with fine spherical and coarse plate-like shapes, were formed in the γ’-based single crystals by annealing at 1073K for 3h (peak-aged) or 100h (over-aged), respectively. The over-aged samples exhibited stronger cyclic hardening than did the peak-aged ones; although the yield stress of the peak-aged material was higher than that of the over-aged material. In these 2 crystals, the precipitates were sheared by superlattice dislocations which had dissociated into super-partials. The separation distance between the super-partials increased in the precipitates because there was no antiphase boundary in the disordered phase and cyclic hardening was enhanced in the aged crystal. The sizes of the precipitates in the over-aged crystal were reduced by shear deformation, resulting in an acceleration of the cyclic hardening. Dissolution of the γ phase in the γ’ matrix did not occur during cyclic loading, and cyclic softening did not appear.

Cyclic Deformation Behaviour of γ’-Ni3(Al,Ti) Single Crystal Containing Disordered γ Precipitates. H.Y.Yasuda, R.Jimba, Y.Umakoshi: Acta Materialia, 2002, 50[1], 161-9