Effects of distributed Fe particles on low-cycle fatigue behavior of Cu–Fe alloy single crystals

Low-cycle fatigue behavior of Cu–1.58mass.%Fe alloy single crystals with precipitated f.c.c. γ-Fe particles was examined under plastic strain controlled tests. Specimens with large (about 100 nm in diameter) and small (30 nm) particles were prepared. Although the γ-Fe particles are coherent and shearable, no cyclic softening was observed in specimens with large particles. On the other hand, in small-particle specimens, cyclic softening was observed particularly at lower strain amplitudes. Dislocation microstructures characteristic of cyclic deformation were more clearly developed in large-particle specimens. Magnetic measurements of fatigued specimens revealed that more particles had transformed martensitically into b.c.c. α-Fe in large-particle specimens than in small-particle specimens. The transformation changes the particle character from ‘coherent and shearable’ to ‘incoherent and nonshearable’. This change enhances the uniform deformation and the absence of cyclic softening in the large-particle specimens where the majority of the particles became α-Fe.