An inverse Hall–Petch effect has been observed for nanocrystalline materials by a large number of researchers. This effect implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation-based models, diffusion-based models, grain-boundary-shearing models and two-phase-based models. In this paper, w...

The experimental evidence for the Hall-Petch dependence of strength on the inverse square-root of grain size is reviewed critically. Both the classic data and more recent results are considered. While the data are traditionally fitted to the inverse square-root dependence, they also fit well to many other functions, both power law and non-power law. There have been difficulties, recognized for ...

Mechanical strengthening by grain refinement is a method whereby a material’s strength and hardness can be increased by decreasing the average crystallite grain size. The empirical Hall–Petch relationship mathematically describes grain boundary strengthening and provides guidance for a straightforward way to produce stronger materials. While the phenomenon has been widely explored in nanocrysta...

In this study, a comprehensive investigation on nano-scale machining of polycrystalline copper structures is carried out by molecular dynamics (MD) simulation. Simulation cases are constructed to study the impacts of grain size, as well as various machining parameters. Six polycrystalline copper structures are produced, which have the corresponding equivalent grain sizes of 5.32, 6.70, 8.44, 13...

Abstract The strength of polycrystal increases as the grain diameter l decreases, i.e. Hall–Petch behaviour. This trend reverses at about 3 < 15 nm, inverse-Hall–Petch How size affects material’s nm (~12 particles) remains unclear. Here our simulations use mixtures soft and hard particles so that compression can continuously reduce to merely a few particles, resulting in ultrafine-grained so...

Nanocrystalline materials show a higher strain-rate sensitivity in contrast to the conventional coarse-grained materials and a different grain size dependency. To explain these phenomenon, a finite element model is constructed that considers both grain interior and grain boundary deformation of nanocrystalline materials. The model consist of several crystalline cores with different orientations...

the mechanical properties and microstructural developments of 321 stainless steel during thermomechanicalprocess were investigated. the repetitive cold rolling and subsequent annealing wereconducted to achieve nanocrystalline structure in an aisi 321 stainless steel. heavily cold rolling at−20°c was conducted to form martensite in metastable austenitic steel. the process was followed byannealin...

The elastic and vibrational properties of iron-nickel and aluminum nanoparticles and nanocrystalline materials have been investigated on the basis of molecular dynamics simulations and the embedded atom method for the description of the materials. It is well known that nanocrystalline solids, with grain sizes in the nanometer range, exhibit often unsual properties like increased hardness due to...