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 si ngle crystals was investigated focusing on stress-strain response and defor mation substructure. The cyclic hardening depended strongly on the long ran ge order. The maximum stress in the disordered crystals increased gradually with increasing number of cycles and then reached a saturation, while orde red ones exhibited cyclic softening after an initial strong cyclic hardenin g. The cyclic hardening at an early stage of fatigue in ordered crystals ma y be due to APE tubes and debris which were produced by the intersection be tween primary and secondary slips. Coarse slip bands were observed in fatig ued ordered Ni3Fe single crystals. In the bands, three-dimensional dislocat ion 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.