Abstract
Correlations between the tensile mechanical properties and ordering processes have been investigated for Ni3Fe polycrystals, containing iron in the range 20-30 at%. The yield stress first increased gradually, reached a peak, and then decreased to a constant value, being similar to the change of yield stress of single crystals. The most rapid change of the yield stress with ordering time occurred in 27.5 at%Fe alloys which had the highest order-disorder transformation temperature. The stoichiometry effect on the yield stress in the disordered state was interpreted by solid solution strengthening of Fe atoms in Ni while that in the ordered state was explained by defect strengthening of the anti-structure. The phenomenon of the discontinuous yielding accompaying Lüders deformation was found in the ordered state. As ordering proceeds, elongation first made a faint plateau and then decreased to a constant value, the level of which was lower than that of an initial (disordered) state. Correspondingly, the reduction in area of alloys decreased and the intergranular fracturing occurred in some areas. It was suggested that the elongation loss of Ni3Fe polycrystals was caused by the decrease of the grain boundary (cohesive) strength due to the change in atomistic structure and bond nature of the grain boundary plane created by ordering.
