Effect of long-range order on the cyclic deformation behaviour of Ni3Fe single crystals

Effect of ordering on cyclic deformation in disordered and ordered Ni3Fe single crystals was investigated focusing on stress-strain response and deformation substructure. The cyclic hardening depended strongly on the long range order. The maximum stress in the disordered crystals increased gradually with increasing number of cycles and then reached a saturation, while ordered ones exhibited cyclic softening after an initial strong cyclic hardening. The cyclic hardening at an early stage of fatigue in ordered crystals may be due to APE tubes and debris which were produced by the intersection between primary and secondary slips. Coarse slip bands were observed in fatigued ordered Ni3Fe single crystals. In the bands, three-dimensional dislocation structure was formed accompanied by a decrease in the degree of order, which was responsible for the cyclic softening. (C) 2000. Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.