No abstract

Due to a high propensity of nano-particles to agglomerate, making aluminium matrix composites with a uniform dispersion of the nano-particles using liquid routes is an exceptionally difficult task. In this study, an innovative approach was utilised to prevent agglomeration of nano-particle by encapsulating SiC nanoparticles using graphene sheets during ball milling. Subsequently, the milled mixture was incorporated into A356 molten alloy using non-contact ultrasonic vibration method. Two different shapes for graphene sheets were characterised using HRTEM, including onion-like shells encapsulating SiC particles and disk-shaped graphene nanosheets. This resulted in 45% and 84% improvement in yield strength and tensile ductility, respectively. The former was ascribed to the Orowan strengthening mechanism, while the latter is due primarily to the fiber pull-out mechanism, brought about by the alteration of the solidification mechanism from particle pushing to particle engulfment during solidification as a consequence of high thermal conductive graphene sheets encapsulating SiC particles. Due to a high propensity of nano-particles to agglomerate, making aluminium matrix composites with 13 a uniform dispersion of the nano-particles using liquid routes is an exceptionally difficult task. In this 14 study, an innovative approach was utilised to prevent agglomeration of nano-particles by 15encapsulating SiC nano-particles using graphene sheets during ball milling. Subsequently, the milled 16 mixture was incorporated into A356 molten alloy using non-contact ultrasonic vibration method. Two 17 different shapes for graphene sheets were characterised using HRTEM, including onion-like shells 18encapsulating SiC particles and disk-shaped graphene nanosheets. This resulted in 45% and 84% 19improvement in yield strength and tensile ductility, respectively. The former was ascribed to the 20Orowan strengthening mechanism, while the latter is due primarily to the fiber pull-out mechanism, 21 brought about by the alteration of the solidification mechanism from particle pushing to particle

Size effect is a special phenomenon in metal micro-forming process. As the deformation process is scale down to micro/mesoscale, the characteristics of single grain involved in the deformed region play a significant role on the material mechanical behaviours resulting in the invalidation of classical theories in microforming. This paper presents a newly developed material model in microscale on the basis of the grained heterogeneity (e.g. grain size, shape and deformability) and specimen dimension. Voronoi tessellation has been employed to describe the polycrystalline aggregate. The grain shape is controlled by the centroidal-voronoi algorithm to drive grains into steady state. Hardness of the grains obtained from Nano-indentation is used to identify the scatter of the grained deformability. Applying the new material model, the micro-compression test of pure copper is numerically simulated by finite element method (FEM). The influences of grain size and feature size on the deformation behaviours are discussed. The numerical simulation results are in good agreement with the experimental results in terms of the flow stress curves and profile of deformed parts. Based on the novel material model, a FE model of microcross wedge rolling is established and the obtained results show the strain of specimen core region increases with the magnification of grain size. © 2013 Elsevier B.V. All rights reserved. AbstractSize effect is a special phenomenon in metal micro-forming process. As the deformation process is scale down to micro/meso scale, the characteristics of single grain involved in the deformed region play a significant role on the material mechanical behaviours resulting in the invalidation of classical theories in microforming. This paper presents a newly developed material model in micro scale on the basis of the grained heterogeneity (e.g. grain size, shape and deformability) and specimen dimension. Voronoi tessellation has been employed to describe the polycrystalline aggregate. The grain shape is controlled by the centroidal-voronoi algorithm to drive grains into steady state. Hardness of the grains obtained from Nano-indentation is used to identify the scatter of the grained deformability. Applying the new material model, the micro-compression test of pure copper is numerically simulated by finite element method (FEM). The influences of grain size and feature size on the deformation behaviours are discussed. The numerical simulation results are in good agreement with the experimental results in terms of the flow stress curves and profile of deformed parts. Based on the novel material model, a FE model of micro cross wedge rolling is established and the obtained results show the strain of specimen core region increases with the magnification of grain size.

No abstract

No abstract