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Abstract: Workability and mechanical properties of the ultrasonically cast Al–X wt% Al2O3 (X=2, 3.57 and 4.69) metal matrix nanocomposites were reported in the present investigation. The Al–Al2O3 (average size ∼10nm) composites showed maximum reduction ratios of 2, 1.75 and 1.41 at room temperature, and 8, 7 and 6 at 300°C. The elastic modulus, nanoindentation hardness, microhardness and Vickers hardness were measured on the as-cast, cold and hot rolled specimens. The tensile properties were also evaluated for the as-cast composites for different wt% of reinforcement. The microstructural examination was done by optical, scanning and transmission electron microscopy. The strength and workability of the nanocomposites were discussed in the light of dislocation/particle interaction, particle size and its concentration, inter-particle spacing and working temperature. 2wt% of Al2O3 reinforcement showed better combination of workability and mechanical properties possibly due to better distribution of particulates in the matrix. [Copyright &y& Elsevier]

Abstract Nanofluids are a new group of materials with potentially broad applications in the industry, especially in the process of heat transfer. Recently, a new class of nanofluids called hybrid nanofluids are being used to enhance the heat transfer rate. In the present study, an experimental investigation on heat transfer characteristics of aqueous Al 2 O 3 /Ag hybrid nanofluids is presented. The main idea in producing hybrid nanofluids was to obtain better heat transfer rate compared to nanofluids dispersed with either of the dispersoids. The detailed surface properties of Ag and Al 2 O 3 nanoparticles were performed by X-ray diffraction and transmission electron microscopy. Polyvinylpyrrolidone used to stabilize the nanoparticles (Al 2 O 3 /Ag) in water. Dynamic light scattering and zetapotential measurements measured the particle size distribution of the nanoparticles in the nanofluid and the surface charge formed on the surface of the nanoparticle by the polyvinylpyrrolidone. The hybrid nanofluid was prepared by dispersing Al 2 O 3 /Ag (50,50) in distilled water, and the thermal conductivity measurements were conducted for particle loading varying from 0.005 vol% to 0.1 vol% using transient hot-wire method. The results indicate that Al 2 O 3 /Ag hybrid nanofluids exhibit higher thermal conductivity enhancement compared to Al 2 O 3 nanofluids alone. Based on the experimental data, a new correlation for predicting the thermal conductivity of aqueous Al 2 O 3 /Ag has been proposed. Graphical abstract Unlabelled Image Highlights • Two-step method has been employed to prepare aqueous Al2O3/Ag hybrid nanofluid. • Al2O3/Ag nanofluids exhibited higher thermal conductivity compared to Al2O3 nanofluid. • Proposed new correlation to predict the thermal conductivity of Al2O3/Ag nanofluids. [ABSTRACT FROM AUTHOR]

Abstract: An investigation on the structure of an ultrasonically cast nanocomposite of Al with 2wt.% nano-sized Al2O3 (average size ∼10nm) dispersoids showed that the nanocomposite was consisting of nearly continuous nano-alumina dispersed zones (NDZs) in the vicinity of the grain boundaries encapsulating Al2O3 depleted zones (ADZs). The mechanical properties were investigated by nanoindentation and tensile tests. The nano-sized dispersoids caused a marginal increase in the elastic modulus, and a significant increase in the hardness (∼92%), and tensile strength (∼48%). Subsequent cold rolling to achieve a reduction ratio of 2 resulted in an appreciable increase in the hardness due to change in morphology of the microstructure. Estimation of the strength on the basis of inter-particle spacing, which was measured by transmission electron microscopy, could not be accounted for on the basis of Orowan mechanism, and therefore, strengthening mechanisms like local climb and/or cross slip might have a role in this room temperature (0.32T M) deformation process. [Copyright &y& Elsevier]