Cyclic deformation behaviour of γ′-Ni3(Al, Ti) single crystal containing disordered γ precipitates

Effect of disordered gamma precipitates on the cyclic deformation behaviour of gamma'-Ni-3(Al,Ti)-based single crystals with L1(2) structure was investigated. The gamma precipitates with fine spherical and coarse plate-like shapes were formed in the gamma'-based single crystals by annealing at 1073 K for 3 h (peak-aged) and 100 h (over-aged), respectively. The over-aged crystal shows stronger cyclic hardening than does the peak-aged crystal, although the yield stress of the peak-aged crystal is higher than that of the over-aged one. In these two crystals the precipitates were sheared by superlattice dislocations dissociated into superpartials. The separation distance between superpartials increased in the precipitates because there was no APB in the disordered phase and the cyclic hardening was enhanced in the aged crystal. The size of the precipitates in the over-aged crystal was reduced by shear deformation resulting in acceleration of the cyclic hardening. Dissolution of gamma phase into gamma' matrix did not occur during cyclic loading and cyclic softening did not appear. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.