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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: We report here successful synthesis of Al-based nanocomposites with L12–Al3Ti particles in binary Al–Ti (4.1, 5, 8.3, 10, 15 and 20% Ti) and ternary Al-1.6Ti-0.5Cr, Al-3.2Ti-1.0Cr and Al-6.3Ti-2.0Cr alloys, by rapid solidification processing. The microstructure of all the alloys consists of uniform distribution of nanocrystalline L12–Al3Ti intermetallic in ultra-fine α-Al matrix. The volume fraction of L12–Al3Ti phase in the as-spun ribbons was found to increase with the Ti content in the binary alloys with exception of Al-20% Ti alloy, which formed equilibrium DO22–Al3Ti. The α-Al grains were measured to be in the size range 0.5–1.0μm embedded with L12–Al3Ti particles of ∼50nm diameter. Nanoindentation as well as microhardness of nanocomposites in binary Al–Ti alloys measure hardness value of 3.75GPa (367 VHN). The nanocomposites formed by rapid solidification processing retain about 70–85% of its room temperature hardness even at 500°C for 100h, while the hardness of conventional Al alloys such as 2017 is almost lost at 350°C in 30min. [Copyright &y& Elsevier]

Abstract: The present paper reports the formation of nanocomposites containing α-Al and L12–Al3Ti in binary Al–Ti alloys containing 5, 10, 15, and 20at.% Ti. Supersaturated solid solution of Ti in Al was observed after 20h of mechanical alloying irrespective of the Ti content. Nanocomposites formed after mechanical alloying and subsequent annealing at 673K for 2h showed a high hardness (3.4GPa), modulus (106.4GPa) and density (95%). Hardness values of Al–(L12)Al3Ti nanocomposites obtained by nanoindentation were similar to hardness measured with microhardness. High strength of the nanocomposites was attributed to the formation of large volume fraction of nanocrystalline L12–Al3Ti particles and the ultrafine grain size of α-Al matrix. [Copyright &y& Elsevier]

Abstract: Nanocrystalline L12-Al3(Ti,Zr) intermetallic has been synthesized directly by mechanical alloying of elemental blends of the nominal composition Al75(Ti25−x Zr x ) for x =0, 5, 10, 15, 20 and 25. The long range order parameter is found to increase with the Zr content. The lattice parameter difference between the L12-Al3(Ti,Zr) and Al was minimum for the alloy with 10% Zr. A very high hardness of 3.23GPa was achieved for the L12 phase in the Al75Ti15Zr10 composition in the green compact condition with a relative density of 77.6%. [Copyright &y& Elsevier]

A simplified model was developed to determine the temperature of the powder particles at the point of collision during mechanical alloying (MA). The model showed that the temperature reached a maximum of ∼473 K within 4–6 h of MA of a ternary blend of Al35Ni35Fe30 with the formation of AlNi phase. [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]

Transient hot-wire and laser flash methods are the two commonly used techniques for measuring the thermal conductivity of nanofluids. However, a comparative study of these two techniques considering identical nanofluids has not been carried out. In this regard, the current study aims at comparison of two methods with identical distribution of Al 2 O 3 and Ag nanoparticles in water. The study also accounts quantitatively for the wide difference in the measured thermal conductivities on the basis of the flux of nanoparticles across the thermal boundary layer resulting from the Brownian movement. It has been observed that the collision flux of the nanoparticle increases with increase in the initial perpendicular distance of the nanoparticle from the heat source wall. Such an increase results in higher thermal conductivity in case of transient hot-wire compared to laser flash method. [ABSTRACT FROM AUTHOR]

Abstract: The influence of bulk stoichiometry of the nano-dispersoids’ and their surface composition/state on the stability and thermal conductivity of water based nanofluids has been investigated for the first time using mechanically alloyed NiAl intermetallic nanopowders produced from stoichiometric (Ni50Al50) and non-stoichiometric (Ni40Al60 and Ni65Al35) compositions. X-ray diffraction patterns of the ball milled products have evidenced that only NiAl phase is present in all the three compositions studied after milling for 30h, and the NiAl crystallite size in these milled powders is in the range of 8–12nm. The addition of 0.1 vol.% mechanically alloyed Ni65Al35 nanoparticles increases the thermal conductivity of the base fluids by ∼28% and the enhancement in the thermal conductivity increases linearly with the particle loading in the range of 0.1 vol.% to 0.25 vol.%. The visual observation as well as thermal conductivity measurements of the NiAl dispersed aqueous nanofluids manifest longer stability (∼7days), when the NiAl dispersoid is of Ni65Al35 composition, as compared to the stability of NiAl dispersion of Ni40Al60 composition (∼6h) or Ni50Al50 composition (∼5days). The results are interpreted using the FTIR analysis, zeta potential measurements, UV–vis spectrometry and the existing data of the X-ray photoelectron spectroscopy in the literature for the surface states of the ball milled NiAl powders. [Copyright &y& Elsevier]

Abstract: Nanofluids often exhibit significantly higher thermal conductivity compared to the base fluid. Contributions of the phononic and electronic thermal transport between a heat source and frequently colliding nanoparticles to the enhanced thermal conductivity have been investigated for the first time, through multi-scale modeling. Classical molecular dynamics (MD) model has been used to estimate the phononic component of thermal transport from the heat source to colliding nanoparticles. A meso-continuum model has been used to estimate the same as well as the thermal transport from heat source to colliding nanoparticle due to the combined effect of phononic and electronic mechanisms. The data on thermal pickup by colliding nanoparticles from the heat source, obtained by rationally combining the predictions of MD and meso-continuum approach, have been fed to a higher length scale stochastic model to estimate the enhancement in the conductivity. The stochastic model keeps track of Brownian movement of nanoparticles within the base fluid and the convective heat dissipation of the absorbed thermal energy of the nanoparticles to the surrounding fluid. The present multi-scale model estimates ∼74% thermal conductivity enhancement in water-based silver nanofluid (0.1 vol%) having nanoparticles in the size range of 4–30nm, and the results are in reasonable agreement with the experimental results reported in the literatures. [Copyright &y& Elsevier]

Abstract: The nanostructured phases formed in the elemental powder blends of nominal compositions Al92Mn6Ce2 and Al93Mn6Ce1 during mechanical alloying were investigated by X-ray diffraction and transmission electron microscopy. The difference in Ce content in the two alloys strongly influenced the types of the intermetallic phase(s) formation, including those of the Ce-free phases. Partial amorphization observed in Al92Mn6Ce2 after prolonged (60 h) milling was not apparent in the lower Ce bearing alloy. Analysis of the X-ray diffraction data of these alloys along with those reported in the literature indicated the dominant role of the topological factors in the amorphous phase formation by mechanical alloying of the concerned system. The phases present in the mechanically alloyed Al92Mn6Ce2 were entirely different from those reported for rapid solidification processing of the same composition [A. Inoue, Nanostruct. Mater. 6 (1995) 53–64.]. Moreover, the phases present in the mechanically alloyed powder showed inferior thermal stability, when compared to that reported for the rapidly solidified product, apparently due to the difference in the nature of structural disorders and strain induced in the products by the two non-equilibrium processing routes. [Copyright &y& Elsevier]

Abstract: The aim of the present work is to produce aluminum matrix nanocomposite powders by displacement reaction between aluminum and ceria and to study the effect of high-energy ball milling on the onset temperature for the reduction reaction. If the onset temperature for the reduction reaction in the milled products during subsequent thermal treatment can be brought down below the melting temperature of the constituents, the reaction product can have very fine structure. This in turn accelerates the consolidation by lowering the sintering temperatures. Two different approaches, pure mechanosynthesis and combined mechanical and thermal synthesis, have been investigated to synthesize aluminum matrix nanocomposite powders by displacement reaction between aluminum and ceria. The ingredients have been subjected to high-energy ball milling up to 100h in a planetary ball mill with hardened chrome steel grinding media. Differential thermal analysis, X-ray diffraction and electron microscopy have been used to study onset temperature for the reduction reaction and reaction mechanism. High-energy ball milling of the powder modifies the reactivity of the system and refinement of microstructure is accompanied by nanometer range crystallites and an increase in the lattice strain. The onset temperature for the displacement reaction has been reduced from 960 to 690°C after 5h of milling. An increase in the milling time up to 30h changes the reaction to a solid-state reduction reaction. It has been shown that an appropriate combination of mechanical–thermal treatment may lead to the synthesis of aluminum-based nanocomposites by the solid-state processing. [Copyright &y& Elsevier]

Abstract: Sintering and cyclic oxidation behavior of nanostructured W–Cr alloys having 30, 50 or 60at.% Cr, prepared through mechanical alloying of elemental blends have been investigated. Relative density of 96–97.5% could be achieved by sintering at 1700°C. X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy have shown the presence of W-rich and Cr-rich phases in sintered alloys. The oxidation resistance during exposure at 800°C is found as the highest in the W0.4Cr0.6 alloy, while that at 1000°C and 1200°C appears to be the best for the W0.5Cr0.5 alloy. Relatively finer and more uniform distribution of the Cr-rich phase in microstructure of the W0.5Cr0.5 alloy appears to be responsible for its superior oxidation resistance. The Cr2O3 is found to be primarily responsible for protection against oxidation at 800°C, while the formation of Cr2WO6 appears to have more significant role at ≥1000°C. [Copyright &y& Elsevier]

Abstract: The irradiation effects of 6MeV electrons on the electrical properties of Al/TiO2/n-Si metal–oxide–semiconductor capacitors have been investigated. Nine Al/TiO2/n-Si capacitors were fabricated using radio frequency magnetron sputtering and divided into three groups. Groups were irradiated with 6MeV electrons at 10, 20, and 30kGy doses, respectively, keeping the dose rate ∼1kGy/min. The variations in the capacitance–voltage and leakage current–voltage characteristics, in addition to the electrical parameters, such as conductance (G/ω), flat-band voltage, interface trap density and the surface charge density with electron dose were studied. The Poole–Frenkel coefficient of the MOS capacitors was determined from current–voltage characteristics. Possible mechanisms for the enhanced leakage current in the electron irradiated MOS capacitors are discussed. [Copyright &y& Elsevier]

Abstract: Titanium nitride and titanium oxynitride films were deposited by varying the plasma current density from 10 mA/cm2 to 40 mA/cm2 using DC magnetron sputtering at constant gas flow rate and deposition time. Samples were characterized by Grazing Incidence X-Ray Diffraction, XPS, Nanoindentation and colorimetric analysis. Different coloured films like golden, blue, pink and green were obtained at different current densities. At lower current density (10 mA/cm2), golden coloured stoichiometric titanium nitride film was formed. At higher current densities (20, 30 and 40 mA/cm2), non stoichiometric Titanium oxynitride films of colour blue, pink and green were formed respectively. The thickness of the films increased with plasma current density from 43 nm to 117 nm. It was found that the colour variation was not only due to thickness of the film but also due to oxygen atoms replacing the nitrogen positions in TiN lattice. Hardness and Young Modulus of the films were found to decrease from 17.49 GPa to 7.05 GPa and 319.58 GPa–246.77 GPa respectively with increasing plasma current density. This variation of hardness and Young Modulus of the films can be speculated due to change in crystal orientation caused by oxygen incorporation in the films. The film resistivity increased from 16.46 × 10−4 to 3.28 × 10−1 Ω cm for increasing plasma current density caused due to oxygen incorporation in the crystal lattice. [Copyright &y& Elsevier]

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]

The present study concerns laser surface nitriding of Ti–6Al–4V. The microstructure of the surface nitrided Ti–6Al–4V consisted of TiN dendrites distributed in alpha Ti matrix. The microhardness of the surface was improved to 1142VHN as compared to the 260VHN of substrate. The bulk modulus of the surface was increased to 177GPA as compared to the 114GPA of the substrate. The pitting corrosion resistance and wettability were significantly improved against simulated body fluid. [Copyright &y& Elsevier]