Atomistic simulation of mechanical behaviours of nanocrystalline AI alloys with grain boundary segregation

Abstract

Bulk nanocrystalline (NC) metals and alloys demonstrating very high ultimate strength compared to conventional coarse-grained materials have a great potential for structural applications. However, their usage is limited due to low ductility and premature intergranular fracture at ambient conditions. An increase in resistance of NC metallic materials against cracking along grain boundaries (GBs) is one of the important tasks of materials science. It is believed that the possible method for their mechanical property improvement is to utilize GB segregation hardening which can be expected only for materials having very dense GB networks. Therefore, the PhD research aims to understand the mechanical behaviours of NC aluminium (Al) with GB segregation of various alloying elements through numerical simulation.The effects of different additional elements in GBs of NC Al on the elastic-plastic, fracture and cyclic behaviours are systematically studied with the consideration of the embrittlement potency, stress-strain relation, structure evolution and deformation mechanisms of the materials via molecular statics (MS) and molecular dynamics (MD) simulations.In order to estimate the ability of impurity elements such as Fe, Co, Cu, Ti, Mg and Pb to resist brittle GB separation in NC Al, the GB segregation energy and the embrittlement potency for the mentioned elements located at different GBs of Al bicrystals are calculated using the MS simulation. It is shown that the Co atom in GBs of the Al bi-crystals has a noticeable positive effect on the GB strength, while Pb has a negative effect. These results are compared with those obtained by conducting the MD simulation of the stress-strain test for NC binary Al alloys with GB segregation. It is

Molecular dynamics study on the deformation and fracture of FeCo-based alloys

“…Therefore, to assess result variability, straining tests were conducted along the principal directions of the Cartesian plane. This approach has been employed in both experimental and computational studies to evaluate elastic anisotropy in nanocrystalline systems [240][241][242][243]. A representation of the model strained along the [001] axis can be observed in The stress-strain curves exhibit a consistent pattern: stress builds up in an almost linear manner, followed by continuous yielding without a sudden shift from elastic to plastic deformation.…”