Solidification behaviour,microstructure and mechanical properties of high Fe-containing Al–Si–V alloys

The paper deals with effect of Fe on the solidification behaviour and mechanical properties of unmodified and modified Al–V–Si alloys. Effect of thermo-mechanical processing on the mechanical properties of these alloys was also reported. The solidification proceeds through several invariant reactions, the first one corresponds to formation of Al₃(Fe,V,Si)-type phase. Modification with Ni–Mg master alloy changes the morphology, size and distribution of the primary as well as interdendritic phases. The modified alloys show an increase in first invariant reaction temperature and decrease in final invariant reaction temperature when compared with unmodified alloy, probably due to action of phase modification. In comparison to untreatable alloy, appreciable improvement in mechanical properties occurs on modification by Ni–Mg treatment. Hot rolling further improves the mechanical properties of the alloy.     

A comparative study of YBCO powders prepared by different processes

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

High-frequency scattering from a wedge with impedance facesilluminated by a line source. I. Diffraction

The canonical problem of evaluating the scattered field at a finite distance from the edge of an impedance wedge which is illuminated by a line source is considered. The presentation of the results is divided into two parts. In this first part, reciprocity and superposition of plane wave spectra are applied to the left far-field response of the wedge to a plane wave, to obtain exact expression for the diffracted field and the surface wave contributions. In addition, a high-frequency solution is given for the diffracted field contribution. Its expression, derived via a rigorous asymptotic procedure, has the same structure as that of the uniform geometrical theory of diffraction (UTD) solution for the field diffracted by a perfectly conducting wedge. This solution for the diffracted field explicitly exhibits reciprocity with respect to the direction of incidence and scattering     

An expert system for the design and selection of ball bearing parameters

Artificial Intelligence (AI) is an emerging technology. Research in Al is focused on developing computational approaches to intelligent behaviour.The computer programs with which AI could be associated are primarily processes associated with complexity, ambiguity, indecisiveness, and uncertainty. One of these computer programs is referred to as Knowledge-based Expert System (KBES) as it represents knowledge acquired from various experts in a particular field of interest to the user. The expert system emulates human behaviour in solving problems thought to require experts for their solution by utilizing computer programs that incorporate experts' heuristic reasoning. In this paper, the application of KBES to aid the design of ball and roller bearing is discussed. The precision rolling-element bearing of the twentieth century is a product of exacting technology and sophisticated science. A bearing supports radial and axial loads, at the same time allowing relative motion between two elements of a machine. Various requirements and steps in the design of ball and roller bearings are discussed. Equations are developed for the relevant design parameters and input into the expert system shell called VP-Expert. The expert system rules are also provided.     

Structural damage in ZnO bombarded by heavy ions

The effect of implantation parameters on damage build-up in ZnO bombarded with Bi and Er ions is studied by Rutherford backscattering/channelling spectrometry. The results show that the damage accumulation behaviour in ZnO is different dramatically from that in other semiconductors. In particular, a variation of implantation parameters, such as collision cascade density, sample temperature and ion flux, has only a minor influence on the damage accumulation in the crystal bulk for the case of such heavy ions. Moreover, an intermediate damage peak, between the surface and bulk defect peaks, is observed for all the irradiation conditions studied. The cascade density affects the behaviour of this intermediate peak with increasing ion dose.     

Improvement in shape memory in magnesium niobate modified PZST

A modified lead zirconate stannate titanate system (PZST) has been studied for shape memory effect. Addition of magnesium niobate (MN) slows down the dipole relaxation process, leading to increased (∼3-fold improvement) remnant strain in the PZST system (0.99PZST–0.01PMN). Room temperature X-ray diffraction patterns before poling (antiferroelectric (AFE) tetragonal) and after poling (ferroelectric (FE) rhombohedral), clearly demonstrate that the transition to the ferroelectric phase is stable even in the absence of any electric field. A small applied electric field (∼1.7 kV/cm) in the opposite direction was required to bring the sample back to its original shape. Field-induced strain butterfly loops taken at 50 Hz show that the material response time is quite small.     

Room temperature synthesis of highly hemocompatible hydroxyapatite, study of their physical properties and spectroscopic correlation of particle size

Needle shaped nanoparticles of hydroxyapatite (HA) have been synthesized at room temperature using orthophosphoric acid as the source of (PO4)3- ions, while calcium chloride, the calcium source, is suitably complexed with citric acid/tartaric acid/acetic acid. The presence of ligands inhibits the growth along [001] and [100] directions of the crystal and thus, helps in formation of needle shaped nanoparticles. The chemical compositions of the samples have been established through AAS and FTIR spectroscopy, while the crystallinity has been assessed through XRD and by the spectral changes in the υ1 and υ3 frequencies of the phosphate group in the respective FTIR spectra. The particle sizes of the samples have been determined from line broadening studies and correlations have been established between the curve fitted percentage area of FTIR and full width half height (FWHH) of the XRD peaks. TEM studies revealed the particle to be needle-shaped with a length and diameter in the range of 20-65 nm and 4-11 nm respectively. Changes in the surface charge of the water dispersed HA samples have been determined at different pH and the isoelectric point for the samples have been found in the range of 3.1-3.4. Finally, the morphology, surface area and hemocompatibility characteristics of the HA samples, prepared by using different complexing agents, have been compared.     

Optical properties of ZnS nanoparticles produced by mechanochemical method

Nanosized zinc sulfide (ZnS) has been synthesized by the mechanochemical route using zinc acetate and sodium sulfide as source materials in a high energy planetary ball mill (HEPBM) with 300 rpm for 2 h. The mechanochemically synthesized powders have been analyzed by X-ray diffraction (XRD) for phase analysis, Field Emission Scanning Electron Microscope (FESEM) for the morphological characterization, UV–vis–NIR spectrophotometer for determining band gap energy and Fluorescence spectroscopy for determining the emission wavelength. The crystallite size of the synthesized ZnS nanoparticles calculated by the Debye–Scherer's formula is in the range 7–9 nm. FESEM morphology shows the fibrous structure of ZnS samples. The value of optical band gap has been found to be in the range 5.2–5.3 eV. Room temperature photoluminescence (PL) spectrum of the samples exhibits a blue light emission using UV excitation wavelength of 280 nm.     

Transforming business through information technology

Information technology has made major strides this past decade, improving significantly the process of doing business. These changes have permeated every aspect of our lives from grocery shopping to banking to manufacturing to managing a profitable business. And the trend is expected to accelerate as we move into the new millennium     

Influence of Varying SiO2?% on the Mechanical Properties of Al Based MMC

The current investigation is focused on effective utilization of rice husk ash (RHA) SiO₂??an industrial waste available in abundance, by systematically dispersing into an Al?CMg (0.5, 1.0, 2.5, and 5.0?% by weight) matrix resulting in synthesis of composites via Liquid Metallurgy route. The effect of increasing Mg?% to improve the wettability with the increase in SiO₂?% as reinforcement was studied comparatively. The increase in the percentage of SiO₂ beyond 5?% as reinforcement into Al?CMg alloy increases the agglomeration of SiO₂ particles which creates more sites for crack initiation and hence lowers down the load bearing capacity of the composite while microhardenss and wear testing analysis. For the composite, Al?CMg (2.5?%)?CSiO₂ (5.0?%) the hardness was observed to be maximum corresponding to minimum wear loss. The uniform distribution of maximum amount of hard spinel structure of extremely small size within the matrix confirms maximum wetting characteristic of 2.5 wt% Mg.