Hall–Petch relationship in a nanotwinned nickel alloy

The Hall–Petch relationship in a nanotwinned alloy with absence of dislocation pile-ups is investigated for the first time. It is shown that, when the twin spacing is large ( d > 150 nm), the hardness exhibits a d −1/2 dependence. However, when the twin spacing is small ( d < 100 nm), a d −1 dependence results. These phenomena are interpreted based on dislocation-mediated mechanisms corroborated by the analysis of electron microscopy and X-ray diffractometry.