Materials Science Forum Vol. 736

Abstract: Phase field models are widely used for the study of microstructures and their evolution. They can also be used as computer experiments. As computer experiments, they serve two important roles: (a) theoretical results which are hard to verify/validate experimentally can be verified/validated on the computer using phase field models; and, (b) when severe assumptions are made in a theory, they can be relaxed in the phase field model, and hence, results with wider reach can be obtained. In this paper, we discuss some such computer experiments in general, and the growth kinetics of precipitates in systems with tetragonal and cubic interfacial anisotropies in particular.

Abstract: Dislocation Dynamics (DD) simulations are used to study the evolution of a pre-specified dislocation structure under applied stresses and imposed boundary conditions. These simulations can handle realistic dislocation densities ranging from 10¹⁰ to 10¹⁴ m^-2, and hence can be used to model plastic deformation and strain hardening in metals. In this paper we introduce the basic concepts of DD simulations and then present results from simulations in thin copper films and in bulk zirconium. In both cases, the effect of orientation on deformation behaviour is investigated. For the thin film simulations, rigid boundary conditions are used at film-substrate and film-passivation interfaces leading to dislocation accumulation, while periodic boundaries are used for bulk grains of Zr. We show that there is a clear correlation between strain hardening rate and the rate of increase of dislocation density.

Abstract: Owing to a large difference in atomic sizes and a positive enthalpy of mixing, Ag and Ni form an immiscible system. In the current work, we report on the electrodeposition of Ag-Ni nanoparticles with a solid solution structure. Effect of current on the relative changes in composition and sizes of solid solution nanoparticles is illustrated. It is shown that with increase in the deposition current, size of Ag-Ni nanoparticles decreases due to an increased nucleation rate. With decrease in size the extent of miscibility of Ni in Ag increases due to increased energetic contribution from the particle curvature.

Abstract: Using first-principle calculations employing density functional theory (DFT) the stabilityof a (3, 3) carbon nanotube (CNT) intercalated with lithium atoms, with respect to their position aswell as Li/C ratio, is studied. On varying the distance of a lithium atom from the axis of the CNT in theradial direction, through the center of a graphitic hexagon, minimum of energy of the system occursat a distance of 3.8 °A from the axis. Keeping the distance of the lithium atom from the tube axis fixedat 3.8 °A, intercalation energy ( E) was calculated while the number of lithium atoms is varied fromone (Li1C12, −0.511 eV) to six (Li6C12, −0.615 eV). It is found that the intercalation becomes morefavorable with the increase in number of lithium atoms intercalated and increase in the symmetryof the intercalated system. The maximum intercalation energy difference between successive lithiumatom additions lay within 0.1 eV.

Abstract: Utilizing molecules for tailoring the exchange coupling strength between ferromagnetic electrodes can produce novel metamaterials and molecular spintronics devices (MSD). A practical way to produce such MSD is to connect the molecular channels to the electrodes of a magnetic tunnel junction (MTJ). This paper discusses the dramatic changes in the properties of MTJ testbed of a MSD due to molecular device elements with a net spin state. When organometallic molecular complexes (OMCs) were bridged across the insulator along the exposed side edges, a MTJ testbed exhibited entirely different magnetic response in magnetization, ferromagnetic resonance and magnetic force microscopy studies. OMCs only affected the ferromagnetic material when it was serving as the electrode of a tunnel junction. Molecule produced the strongest effect on the MTJ with electrodes of dissimilar magnetic hardness. This study encourages the validation of this work and exploration of similar observations with the other combinations MTJs and molecules, like single molecular magnet, porphyrin, and molecular clusters.

Abstract: This paper discusses some theoretical aspects of design of ultralight metallic materials using analytical and heuristic arguments. Potential application of syntactic foams to obtain metal-matrix composites lighter than air is also analyzed. Carbon allotropes (fullerenes, colossal carbon tubes) and some non-carbon materials are considered as components of ultralight metal-matrix composites. Calculations for the size of fullerenes, number of atoms in their structure, and coating thickness required to produce ultralight composites are presented. It is concluded that 3D carbon molecules (fullerenes) and colossal carbon tubes are the most promising components to design ultralight metallic materials which can be lighter than air.

Abstract: The influence of material processing conditions for preparing aluminium based metal matrix nanocomposites through stir casting route is reviewed. The role of particle size with respect to Brownian motion, Stokes settling velocity and strengthening mechanism is assessed from theoretical understandings. Variation of microstructural features and mechanical properties of the nanocomposites are predicted from theoretical concepts and related mathematical models. Experiments conducted to validate the theoretical predictions show that both Orowan and grain refinement strengthening mechanisms remain operative which is the key to the improved strength property of the nanocomposites.

Abstract: Over the years, Aluminium Matrix Composites (AMCs) have gained importance in numerous structural, non-structural and functional applications in different engineering sectors. Driving force for the utilisation of AMCs in these sectors include performance, economics and environmental benefits. The key benefit of AMCs in transportation sector is lower fuel consumption. Particulate reinforced Aluminium Matrix Composites have been successfully used in automotive and aerospace industry due to their light weight, high strength to weight ratio and good wear resistance.This work is focussed on the study of the influence of different composition of reinforcement (Al₂O₃) on physical and mechanical behaviour of Aluminium Matrix Composites. These AMCs will be fabricated by mechanical alloying. In this study instead of aluminium powder aluminium chips will be used along with Al₂O₃ powder with that it is expected that embedment of particles will be better and porosity will be minimised. Once compact are ready these will be sintered and will be evaluated for its various physical, microstructural and mechanical properties.

Abstract: Multifunctional behaviour viz., ferroelectric, ferromagnetic and magnetodielectric coupling has been reported in a number of nanocomposites. The latter were synthesized by growing nanoparticles of different kinds within a suitable matrix. Different morphologies of the particles were introduced. Both natural as well as synthetic mesoporous materials were used to prepare nanocomposite systems. Mesoporous structures with large surface areas and pore volumes were found to be effective in developing most efficient drug delivery systems. For identical reasons such structures were suitable as catalysts in various industrially important reaction processes, as humidity and gas sensors, as magnetic sensors. Mesoporous carbon based nanocomposites used as electrodes were found to improve the efficiency of lithium-ion batteries. Nanocomposites using mesoporous carbon and carbon nanotubes were shown to improve the performance of dye sensitized solar cells. In this article, the above mentioned developments are reviewed and discussed.