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...

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...

This study investigated the grain size dependence of mechanical properties and deformation mechanisms of microcrystalline (mc) and nanocrystalline (nc: grain size below 100 nm) Mg-5wt% Al alloys. The Hall-Petch relationship was investigated by both instrumented indentation tests and compression tests. The test results from the indentation tests and compression tests match well with each other. ...

Nanocrystalline TiN has been imbedded in amorphous silicon nitride matrix to form a super hard nanocomposite thin film (ncTiNya-SiN ) via magnetron sputtering. Adjusting Ti and Si N target power ratio altered film composition, size, amount and x 3 4 distribution of the nc-TiN phase. At a Ti target power density of 5.5 W cm , the Ti to Si N target power ratio should be greater y2 3 4 than unity ...

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...

Grain shapes are acknowledged to impact nanomaterials' overall properties. Research works on this issue include grain-elongation and grain-strain measurements and their impacts on nanomaterials' mechanical properties. This paper proposes a stochastic model for grain strain undergoing severe plastic deformation. Most models deal with equivalent radii assuming that nanomaterials' grains are spher...

An ultra-fine-grained AISI 301LN austenitic stainless steel has been achieved by heavy cold rolling, to induce the formation of martensite, and subsequent annealing at 800 C, 900 C, and 1000 C, from 1 to 100 seconds. The microstructural evolution was analyzed using transmission electron microscopy and the yield strength determined by tension testing. Ultra-fine austenite grains, as small as ~0....

We study the combined effects of grain size and texture on the strength of nanocrystalline copper (Cu) and nickel (Ni) using a crystal-plasticity based mechanics model. Within the model, slip occurs in discrete slip events exclusively by individual dislocations emitted statistically from the grain boundaries. We show that a Hall-Petch relationship emerges in both initially texture and non-textu...

An analytical solution shows that a competition between bond order loss and the associated bond strength gain of the lower coordinated atoms near the edge of a surface dictates the mechanics of the surface and, hence, a nanosolid. Bond order loss lowers the activation energy for atomic dislocation, whereas bond strength gain enhances the energy density or mechanical strength in the region near ...