Materials Science Forum Vol. 736

Abstract: Magnesium nanoparticles were synthesized by using organo magnesium precursor. By changing synthesis parameters such as synthesis time and temperature, various morphologies of the magnesium nanoparticles were obtained. Sample synthesized at 250°C for 30 min exhibited agglomerated nanosheets of magnesium whereas the sample obtained at 2 hour had individual particles consisted of core/shell structure. The corresponding hydrogen storage properties of these samples were also influenced by the morphology. Hydrogen desorption data revealed that samples prepared at 2 hour could release hydrogen at lower temperature (343°C) than those samples prepared at 30 min and 1 hour.

Abstract: Lithium alloying compounds as an anode materials have been a focused for high capacity lithium ion battery due to their highenergy capacity and safety characteristics. Here we report on the preparation of graphite-tin composite by using ball-milling in liquid media. The composite material has been characterized by scanning electron microscope, energy depressive X-ray spectroscopy, X-ray diffraction and Raman spectra. The lithium-ion cell made from graphite-tin composite presented initial discharge capacity of 1065 mAh/g and charge capacity 538 mAh/g, which becomes 528 mAh/g in the second cycle. The composite of graphite-tin with higher capacity compared to pristine graphite is a promising alternative anode material for lithium-ion battery.

Abstract: The development of cobalt alloys for the development of HIP implants has been evolving overtime. Accordingly, in this work an overview of the main microstructural factors that impact the mechanical properties, as well as the effect of interstitials such as carbon and nitrogen. In addition the role alloy pre-straining and heat treating on the amount of ε-martensite and on the exhibited mechanical properties is described. In general, it is shown that as the amount of ε-martensite exceeds 60 vol. percent, the alloy ductility is drastically reduced as the HCP phase becomes dominant in the matrix.

Abstract: Atomic layer deposition (ALD) has been a key player in advancing the science and technology of nanomaterials synthesis and device fabrication. The monolayer (ML) control of growth rate obtained with ALD combined with its ability to self-limit growth reactions at the gas-substrate interface can be exploited in fundamentally new ways to produce novel composite nanomaterials or precisely tailored 3D nanostructures. Fueling the rapid popularity of ALD in nanotechnology research is the relative simplicity of the hardware and exciting new chemistries that allow researchers to deposit a host of new materials including pure metals, metal oxides, sulphides and nitrides and organic thin films with relative ease and superb accuracy. In this review article, we present four impact areas - microelectronics, energy harvesting and energy storage devices and sensors and photonic devices that have benefitted from such an approach. While many excellent review articles are available on the fundamental chemistry of ALD processes, we focus here on the applied science and engineering aspects of cutting edge ALD research

Abstract: The steady state creep behaviour of a rotating FGM disc having linearly varying thickness has been investigated. The disc is assumed to be made of functionally graded composite containing non-linearly varying radial distribution of silicon carbide particles in a matrix of pure aluminum. The creep behaviour of the composite has been described by threshold stress based law. The effect of varying the disc thickness gradient has been analyzed on the stresses and strain rates in the FGM disc. It is observed that the radial and tangential stresses induced in the FGM disc decrease throughout with the increase in thickness gradient of the disc. The strain rates also decrease with the increase in thickness gradient of the FGM disc, with a relatively higher decrease near the inner radius. The increase in disc thickness gradient results in relatively uniform distribution of strain rates and hence reduces the chances of distortion in the disc.

Abstract: Existing standard International methods to estimate fracture toughness of structural materials as documented in ASTM standard E-1820 are neither appropriate for material development due to the requirement of considerable volume nor suitable for process optimizations like deciding suitable heat treatment or for quality control of tonnage materials at the stage of production due to techno-economic reasons owing to their time-consuming nature. This report overviews several investigations often in their feasibility stage and aims to suggest a common solution to all these problems considering measurement of fracture toughness (K_IVM) using chevron notched bend bar specimens with either rectangular cross-section (RC) or circular cross-section (CC). At the outset the theoretical background for obtaining K_IVMRC and K_IVMCC and the corresponding normalized stress intensity factors are discussed in order to illustrate the relatively simpler principle of estimation of fracture toughness. The usefulness of this technique is next illustrated using a number of examples related to: (a) design of small specimens for fracture toughness determination using this principle (b) optimization of the volume fraction of the constituent phases in dual phase steels, (c) design of heat treatment for cast rolls, (d) optimization of cryotreatment for tool steels and (e) study of the effect of inclusions on toughness characteristics of microalloyed steels. The examples related to (a) is for demonstrating the capability of this technique for material development, that related to (b), (c) and (d) are to illustrate its potential for process optimization and the one related to (e) is to illustrate its potential for quality control of tonnage materials.

Abstract: In-situ composites offer a wide selection of constituent and an opportunity for understanding the mechanisms their mechanical properties so that intelligent decisions may be taken while tailoring a composite for a specific application. Properties of material are basically governed by the constituent phases and their distribution and depend on the composition and processing conditions. In the present investigation tribological properties of hot forged Cu-Cr-SiC and annealed after hot forging system are proposed to be studied by addition of Cr and SiC into the copper matrix. The effect of constituent phases on tribological properties after hot forged and annealed after hot forged has been investigated. It is expected to enhance the understanding of tribological properties in this presented work for the hot forged Cu-Cr-SiC composite system.

Abstract: In harnessing clean and renewable energy sources water turbines represent a significant portion of the power generation worldwide. Because of erosion, repair and maintenance of hydraulic turbines is a difficult problem. Material removal in hydraulic turbine components may occur either by particle erosion or cavitation erosion or by their combined action. Many ASTM standard and non standard test rigs are aimed at specific tests, like solid particle erosion, cavitation erosion. To simulate the real conditions in a laboratory setup, a novel method is employed to combine the effect of cavitation erosion and slurry erosion in the slurry pot tester. Triangular prismatic cavitation inducers are used in the conventional slurry pot tester. The aluminum test specimens are investigated in the slurry pot tester. A wide variation in material loss was noted under different exposure conditions. The maximum material loss is ascribed to combined effects of solid particle erosion and cavitation erosion.

Abstract: A model reported by the present investigators has earlier shown that the extent of heat pick up by a nanoparticle during its collision with the heat source in a given nanofluid would depend on the thermal conductivity (k_p, unit W/m.K), density (ρ, unit kg/m³), elastic modulus (E, unit GPa) and Poissons ratio (μ) of the nanoparticle and heat source. Considering the expression for collision period and thermal conductivity of nanoparticle, a factor χ =k_p(ρ/E)^0.4 is proposed here and examined for the preliminary identification of the potential of a dispersoid in enhancing the thermal conductivity of a nanofluid. The χ-factor for Ag, Cu, CuO, Al₂O₃ and SiO₂ are 2960, 2247, 116, 14.1 and 5.5, respectively. The higher χ-factor of CuO compared to that of Al₂O₃ can explain why water and ethylene glycol (EG) based CuO-nanofluid is reported to show higher enhancement in the thermal conductivity, when compared to similar Al₂O₃-nanofluid. The χ for SiO₂ is much smaller than that for Ag, which also corroborates well with the marginal enhancement in thermal conductivity of water based nanofluid containing SiO₂ nanoparticles. Therefore, a high value of χ of the nanodispersoid can serve as a parameter for the design of nanofluids for heat transfer applications.

Abstract: This review article deals with the synthesis, characterization and magnetic properties of Co-Ni nanoalloys. The various physical and chemical methods for the synthesis of Co-Ni alloy nanoparticles are discussed. Co-Ni alloy nanoparticles with different size and shape such as spherical, rods, wires chain-like assembly are found to depend on the synthesis method and experimental condition. The structure of Co-Ni alloys is either fcc, hcp or mixed fcc and hcp phase and found to depends on size, shape and concentration of Co in the Co-Ni alloys. Sodium hydroxide (NaOH) concentration and Co to Ni ratio influence the shape of bimetallic Co-Ni nanoparticles. Pt nucleating agents produced smaller size of Co-Ni alloy particles compared to Ru and Ag. Higher Co concentration in the Co-Ni alloys also influences the size alloy particles. The magnetic properties of Co-Ni nanoalloys depend on the size, shape and composition of the binary alloys. Surface oxidation of Co-Ni alloy nanoparticles decrease the saturation magnetization and increases with Co concentration in the alloys. The shape of Co-Ni alloy nanoparticles has an influence on coercivity. The microwave absorption properties of the Co-Ni alloys found to depend on the shape, size and composition of the binary alloys. The absorbance peaks shifts to higher frequency with decrease in size of the alloy particles. Potential applications of Co-Ni alloys in various fields are highlighted.