Stir casting process for manufacture of Al-SiC composites

Stir casting is an economical process for the fabrication of aluminum matrix composites. There are many parameters in this process, which affect the final microstructure and mechanical properties of the composites. In this study, micron-sized SiC particles were used as reinforcement to fabricate Al-3 wt% SiC composites at two casting temperatures (680 and 850 °C) and stirring periods (2 and 6 min). Factors of reaction at matrix/ceramic interface, porosity, ceramic incorporation, and agglomeration of the particles were evaluated by scanning electron microscope (SEM) and high-resolution transition electron microscope (HRTEM) studies. From microstructural characterizations, it is concluded that the shorter stirring period is required for ceramic incorporation to achieve metal/ceramic bonding at the interface. The higher stirring temperature (850 °C) also leads to improved ceramic incorporation. In some cases, shrinkage porosity and intensive formation of Al4C3 at the metal/ceramic interface are also observed. Finally, the mechanical properties of the composites were evaluated, and their relation with the corresponding microstructure and processing parameters of the composites was discussed

A comparison study of applying metallic coating on SiC particles for manufacturing of cast aluminum matrix composites

Ceramic particles typically do not have a sufficiently high wettability for incorporation into molten metal during aluminum matrix composite manufacturing. Metallic coatings on ceramic particles could improve their wettability by the molten aluminum and hence provide a better bonding between the reinforcement and matrix. In this study, micrometer-sized SiC particles were coated by copper, nickel, and cobalt metallic layers using electroless deposition method. These metallic layers were produced separately prior to ceramic incorporation into molten pure aluminum, in order to compare their effects on the microstructure and mechanical properties of the produced composites. The experimental results showed that copper was the most effective and nickel the least effective of these coating metals for incorporation of the SiC particles into the molten aluminum. It was additionally found that the composite, which contained the copper coated SiC particles, produced the highest microhardness and tensile strength, while that fabricated with the cobalt-coated SiC particles produced the lowest microhardness and tensile strength

Journal of nephrology nursing

In this study, the hot extrusion process was applied to stir cast aluminum matrix–SiC composites in order to improve their microstructure and reduce cast part defects. SiC particles were ball milled with Cr, Cu, and Ti as three forms of carrier agents to improve SiC incorporation. Large brittle ceramic particles (average particle size: 80 μm) were fragmented during ball-milling to form nanoparticles in order to reduce the cost of composite manufacturing. The experimental results indicate that full conversion of coarse micron sized to nanoparticles, even after 36 h of ball milling, was not possible. Multi modal SiC particle size distributions which included SiC nanoparticles were produced after the milling process, leading to the incorporation of a size range of SiC particle sizes from about 50 nm to larger than 10 μm, into the molten A356 aluminum alloy. The particle size of the milled powders and the amount of released heat from the reaction between the carrier agent and molten aluminum are inferred as two crucial factors that affect the resultant part tensile properties and microhardness

Authoring cases from Free-Text Maintenance Data

Automatically authoring or acquiring cases in the case-based reasoning (CBR) systems is recognized as a bottleneck issue that can determine whether a CBR system will be successful or not. In order to reduce human effort required for authoring the cases, we propose a framework for authoring the case from the unstructured, free-text, historic maintenance data by applying natural language processing technology. This paper provides an overview of the proposed framework, and outlines its implementation, an automated case creation system for the Integrated Diagnostic System. Some experimental results for testing the framework are also presented.La cr\ue9ation et l'acquisition automatiques de cas dans le cadre des syst\ue8mes de raisonnement automatis\ue9 par cas (CBR) constituent une probl\ue9matique \ue0 effet d'\ue9tranglement qui peut d\ue9terminer le succ\ue8s ou l'\ue9chec d'un syst\ue8me CBR. Afin de r\ue9duire le travail qui doit \ueatre consacr\ue9 \ue0 la cr\ue9ation de cas, nous proposons un cadre de cr\ue9ation de cas \ue0 partir de donn\ue9es historiques de maintenance, non structur\ue9es et en texte libre, en appliquant la technologie de traitement du langage naturel. Cette communication donne un aper\ue7u du cadre de travail propos\ue9 et d\ue9crit bri\ue8vement son application, un syst\ue8me automatis\ue9 de cr\ue9ation de cas pour le Syst\ue8me de diagnostic int\ue9gr\ue9. Nous pr\ue9sentons \ue9galement des r\ue9sultats relatifs aux essais du cadre de travail.NRC publication: Ye

Solvothermal-assisted graphene encapsulation of SiC nanoparticles: A new horizon toward toughening aluminium matrix nanocomposites

© 2015 Published by Elsevier B.V. Agglomeration of ceramic nanoparticles is a key challenge during manufacturing aluminium matrix composites in both solid and liquid methods. This study presents an innovative fabrication route to diminish the agglomeration of SiC nanoparticles using graphene encapsulating method stimulated by a solvothermal process. The produced SiC nanoparticles were then incorporated into A357 molten alloy using a liquid processing route. HRTEM investigations have shown the uniform distribution of SiC nanoparticles wrapped by onion-liked graphene shells within the matrix of composite, conferring 273% and 400% enhancement in yield strength and tensile ductility, respectively, compared to the unreinforced one. This is attributed to the manipulation of solidification mechanism of SiC nanoparticles from pushing to engulfment, ensued from imparting higher thermal conductivity to these particles by onion-liked graphene sheets. Fractographic observations have revealed the transgranular facture mode activated due to nano-void coalescence fracture mechanism in composites reinforced with graphene sheets associated with prolonged ductility. A devised analytical strengthening model has also demonstrated the profound efficacy of thermal activated dislocation mechanism in fortifying the matrix, brought about by the exceptional negative thermal expansion coefficient of graphene sheets

Enhanced tensile properties of aluminium matrix composites reinforced with graphene encapsulated SiC nanoparticles

© 2014 Elsevier Ltd. 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 nano-particles 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

Strengthening mechanisms of graphene sheets in aluminium matrix nanocomposites

© 2015 Elsevier Ltd. Uniform dispersion of SiC nanoparticles with a high propensity to agglomerate within a thixoformed aluminium matrix was attained using a graphene encapsulating approach. The analytical model devised in this study has demonstrated the significant role of shear lag and thermally activated dislocation mechanisms in strengthening aluminium metal matrix composites due to the exceptional negative thermal expansion coefficient of graphene sheets. This, in turn, triggers the pinning capacity of nano-sized rod-liked aluminium carbide, prompting strong interface bonding for SiC nanoparticles with the matrix, thereby enhancing tensile elongation

Strengthening mechanisms of graphene sheets in aluminium matrix nanocomposites

Uniform dispersion of SiC nanoparticles with a high propensity to agglomerate within a thixoformed aluminium matrix was attained using a graphene encapsulating approach. The analytical model devised in this study has demonstrated the significant role of shear lag and thermally activated dislocation mechanisms in strengthening aluminium metal matrix composites due to the exceptional negative thermal expansion coefficient of graphene sheets. This, in turn, triggers the pinning capacity of nano-sized rod-liked aluminium carbide, prompting strong interface bonding for SiC nanoparticles with the matrix, thereby enhancing tensile elongation

Graphene sheets encapsulating SiC nanoparticles: A roadmap towards enhancing tensile ductility of metal matrix composites

In this study, β-SiC nanoparticles were well dispersed in a matrix of aluminium making use of encapsulation capacity of graphene sheets, semi-solid stirring of the aluminium melt, ultrasonic treatment, and pressure application during solidification. A new solidification model taking into account the alteration of the solidification mechanism from particle pushing to particle engulfment, making use of at least 40% enhancement in higher thermal conductivity and diminished repelling forces of SiC nanoparticles tuned by encapsulating graphene sheets was suggested. This nanostructure manipulation can make about 350% and 258% enhancement in yield strength and tensile ductility, respectively, compared to that of unreinforced aluminum alloy. The results achieved based on the devised analytical model have shown the significant effect of thermal activated dislocation in strengthening due to considerable mismatch between thermal expansion coefficient of graphene sheets and aluminium matrix. Fractographic observations disclosed a dimple fracture surface for the semi-solid-processed aluminium matrix composite reinforced by the nanoparticles that were encapsulated by graphene sheets using ball-milling process compared with the cleavage fracture surface of those fortified without the application of graphene