Size dependent strain rate sensitivity transition from positive to negative in Ti/Ni multilayers

This work presents a length scale dependent strain rate sensitivity (SRS) transition from positive to negative in Ti/Ni multilayers with unequal thickness of individual layer. The multilayers exhibit distinct interfacial structure and no Ti-Ni amorphous intermixed layer between Ni and Ti layers. It can be found that the hardness first increases with strain rate at large modulation period (λ), showing a positive SRS. Subsequently, a tunable (positive to negative) size dependent SRS phenomenon occurs with further decrease of λ. The present negative SRS is attributed to deterioration of the plasticity with decreasing λ and at larger strain rate, which induces microcracks formation.