Modelling and Numerical Computation of Thermal Expansion of Aluminium Matrix Composite with Densely Packed SiC Particles

The coefficient of thermal expansion (CTE) is one of the most important physical properties of metal matrix composites (MMCs). The thermal expansion response is correlated to the microstructure, the deformation of the matrix, and the internal stress conditions. In the present study the physical CTE of aluminium matrix composite (AMC) reinforced with 70 vol. % SiC particles is analytically computed in order to explain abnormalities in the thermal expansion behaviour obtained experimentally. The numerical modelling was carried out from 20oC to 500oC using finite element analysis (FEA) based on two-dimensional unit cell models. These unit cell models are created with particular attention on the effects of microscopic voids and phase connectivity obtained from geometrical factors such as the phase shape and particle distribution. The used unit cell models consider the composites as a continuous rigid phase infiltrated with the ductile Al matrix. The obtained thermal expansion behaviour is strongly influenced by the presence of voids. A comparison of physical CTE with the experimental results shows a good agreement

Highly porous metals and ceramics

none2Cellular solids are a class of highly porous materials that covers a wide range of structures, such as foamed materials, replicated porous or additive manufactured structures, honeycombs, lattice structures, interconnected fibres or hollow spheres and syntactic foams. The pores can be more or less closed or completely open. Depending on their morphology and composition, these materials possess unique properties and are used as components in special and advanced engineering applications. These include filtering liquids and particles in gas streams, porous burners, biomedical devices, lightweight stiff structures, impact absorbers, sound damping modules, thermal management components, etc. The present paper gives an overview on the main fabrication methods and the resulting architectures, in relation to applications of metals and ceramics with >50 vol.-% porosity.noneCOLOMBO P.; DEGISCHER HPColombo, Paolo; Degischer, H

The effect of ball milling and wet blending on the creep behaviour of a particle reinforced 2124 Al-alloy

The creep behaviour of an AW2124 Al-alloy unreinforced and reinforced with 25 vol.% of SiC particles of different sizes is investigated. The materials were produced via powder metallurgy using two powder blending techniques: ball milling and wet blending. The SiC particles are fractured during ball milling resulting in 2-3 vol.% of sub-μm SiC particles. The SiC particles in the wet blended composites are in the μm-range. The creep behaviour of the matrices and the ball milled composites is characterized by a lowstress and a high-stress region. In the low-stress region the creep deformation is governed by viscous drag of dislocations, while climb of dislocations dominates in the highstress region. The high creep resistance exhibited by the ball milled composites is mainly due to the presence of oxide dispersoids introduced during blending of the powders. © Carl Hanser Verlag GmbH & Co. KG.Peer reviewe

In situ synchrotron tomographic investigation of the solidification of an AlMg4.7Si8 alloy.

International audienceThe solidification sequence of an AlMg4.7Si8 alloy is imaged in situ by synchrotron microtomography. Tomograms with (1.4 mu m)(3)/voxel have been recorded every minute while cooling the melt from 600 degrees C at a cooling rate of 5 K min(-1) to 540 degrees C in the solid state. The solidification process starts with the three-dimensional evolution of the alpha-Al dendritic structure at 590 degrees C. The growth of the a-Al dendrites is described by curvature parameters that represent the coarsening quantitatively, and ends in droplet-like shapes of the secondary dendrite arms at 577 degrees C. There, the eutectic valley of alpha-Al/Mg2Si is reached, forming initially octahedral Mg2Si particles preferentially at the bases of the secondary dendrite arms. The eutectic grows with seaweed-like Mg2Si structures, with increasing connectivity. During this solidification stage Fe-aluminides form and expand as thin objects within the interdendritic liquid. Finally, the remaining liquid freezes as ternary alpha-Al/Mg2Si/Si eutectic at 558 degrees C, increasing further the connectivity of the intermetallic phases. The frozen alloy consists of four phases exhibiting morphologies characteristic of their mode of solidification: alpha-Al dendrites, eutectic alpha-Al/Mg2Si "Chinese script" with Fe-aluminides, and interpenetrating alpha-Al/Mg2Si/Si ternary eutectic. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Tensile Deformation and Cracking Sequence of Foamed AlSi10 with Skin

5th Biennial International Conference on Porous Metals and Metallic Foams (MetFoam 2007), Montreal, CANADA, SEP 05-07, 2007International audience28 mm thick panels of cellular AlSi10 were produced by powder compact foaming. Tensile specimens machined from these panels are tested with the original skin on both sides of the samples. The density distribution determined by medical X-ray tomography is transformed into domains of constant densities. The tensile straining of that multiphase continuum is simulated using the finite difference method. The input data for the stiffness and strain hardening are scaled to the domains' densities for the skin and the core of the panel. The stiffness increases slightly with initial straining. Crack initiation is recorded by acoustic emission, while strain hardening continues until complete fracture of a skin. The sequence of crack growth is predicted by the simulation