Hardening-softening transition in pre-annealed and slightly deformed Ni70Fe30 nanoalloy

The Effect of slight deformation on microstructure evolution and microhardness variation in pre-annealed Ni70Fe30 nanoalloy has been investigated. An obvious hardening-to-softening transition is observed at the rolling strain of ∼6%. Further x-ray diffraction analysis and transmission electron microscopy observation reveal a accumulation of dislocation, stacking fault and twin fault before the sample deformed to ∼6%, which is considered the dominant contribution to strain hardening. Moreover, despite of rolling the sample at a relative small strain level, obvious grain growth takes place overall deformation process. With the increasing grain size, Ni70Fe30 nanoalloy enters into strain softening region due to a decrease in the quantity of defect densities when the rolling strain exceeds ∼6%.