Gas tungsten arc welding of titanium using flux cored wire with magnesium fluoride

Abstract

Grade 2 Ti–CP was gas tungsten arc welded using flux cored (FC) wires and flux pastes that contained various MgF₂ contents. The effects of MgF₂ on bead morphology, chemical composition and hardness of weld bead were investigated and interpreted. With an increase of MgF₂ content in the flux paste, depth/width ratio of weld bead increased gradually with little variation in interstitial element contents and hardness. Weld bead made with cold FC wire feed showed even deeper and narrower bead, indicating the greater effectiveness of wire feed than flux paste on weld penetration. While the 50% MgF₂ FC wire produced complete slag coverage and smooth weld bead surface, 85% MgF₂ wire resulted in incomplete slag coverage and rough weld surface. Arc spectroscopy revealed that the 50% MgF₂ FC wire produced plasma spectrum with atomic and ionised titanium peaks, which is an indication of a high temperature arc and a larger amount of flux vapours in the arc. Therefore, it is believed that deep weld penetration associated with high MgF₂ fluxes in this experiment is caused by arc constriction, resulting from the greater amount of flux vapours owing to high arc temperature.     

An idea to treat the dendritic morphology in mixed columnar–equiaxed solidification

Abstract

To treat mixed columnar–equiaxed solidification with dendritic morphology, five phase regions have been distinguished: extradendritic melt, interdendritic melt and solid dendrites in equiaxed grains, interdendritic melt and solid dendrites in columnar arrays of dendrites. These five phases are quantified by their volume fractions, and characterized by different volume-averaged solute concentrations. The equiaxed grains and columnar dendrites are confined by their envelopes, whose shapes are described by morphological parameters. The evolution of the envelopes is derived based on recent growth theories: the growth of primary columnar dendrite tips by the Kurz–Giovanola–Trivedi (KGT) model, the growth of secondary dendrite tips in radial direction of columnar trunk and the equiaxed dendrite tips by the Lipton–Glicksman–Kurz (LGK) model. The solidification of the interdendritic melt is governed by diffusion in the interdendritic melt region. Preliminary modelling results on a benchmark casting (Al–4·7wt-% Cu) show the potentials of the model.     

High performance automotive and railway components made from novel competitive aluminium composites

Abstract

The traditional materials encounter difficulties to comply with all the properties required by new components under service conditions. The automotive and the railway industries require low cost solutions to improve the final performance of components made from steel, cast iron, or even conventional aluminium alloys (e.g. clutch discs, brake discs, or pistons). Weight reduction, improvement in wear behaviour, high thermal conductivity, low coefficient of thermal expansion, and easy recycling are sought, among other characteristics, in order to obtain more efficient products leading to a reduction of pollutant emissions. The range of materials that can meet these requirements is presently very narrow and their final price is more expensive (e.g. aluminium matrix composites) than currently used materials. In this paper a new low cost metal matrix composite that has been used to produce pistons, clutch discs, and train brake discs is presented.     

Hydrogen embrittlement of an HSLA 80 steel in sea water under cathodic charging conditions

Abstract

Hydrogen embrittlement of a copper precipitation strengthened and niobium microalloyed HSLA 80 steel on cathodic charging in synthetic sea water has been studied using a slow strain rate technique. The effects of strain rate and potential applied for hydrogen charging have been studied. Hydrogen measurement at different potentials has also been carried out. A loss in ductility in terms of a drop in percentage elongation and percentage reduction in area has been observed, the effect being prominent at potentials beyond —800 mV(SCE). Fractography by SEM shows a dominance of microvoid coalescence with increasing quasicleavage features at higher negative potentials. A hardening effect of hydrogen charging up to —600 mV(SCE) followed by a softening effect has been observed. The results are discussed in the light of the existing models of hydrogen–dislocation interaction and hydrogen induced microvoid coalescence.     

Adhesion and Wettability Characteristics of Chemically Modified Banana Fibre for Composite Manufacturing

In this work banana fibre was chemically modified using various chemical agents. The surface energy of the fibre is an important parameter and one which governs the interaction of fibre with polymeric matrices. This paper describes the influence of various chemical treatments on the surface energy of the banana fibre investigated by contact angle measurements, spectroscopic analysis and surface morphology studies. The surface energy, work of adhesion, polarity, spreading coefficient, interfacial energy and interaction parameter were determined in the case of raw and chemically modified fibres. Chemical modification has been found to have a profound effect on the surface energy. The polar and dispersive components of the surface energy were also found to be dependent on the chemical treatment involved. The chemical modifications done in this work were: alkali treatment, silanation, benzoylation, formylation, potassium permanganate treatment and acetylation. Of all the modifications, the relative surface energy was found to be a maximum for alkali treated fibre and minimum for silanated fibre. Contact angle measurements were found to be an effective tool in predicting the possible interaction of the fibres with phenol formaldehyde matrix resin. Atomic force microscopy roughness analysis revealed a significant decrease in surface roughness for the chemically modified fibre. An increase both in fibre/matrix adhesion and interfacial shear strength has been observed for all surface modified fibres except for those modified by benzoylation and acetylation.     

Interfacial instabilities in multimaterial co-injection mouldings Part 1 – Background and initial experiments

Abstract

Interfacial adhesion between the skin and core is vital for successful co-injection moulding. This is the first paper in a series, which introduces and describes an in mould method of mixing that is applicable regardless of the compatibility of the materials. It works by inducing turbulent mixing at the interface between the skin and core materials. It makes use of the change that occurs from laminar to turbulent flow at high injection speeds in co-injection moulding. This novel approach takes advantage of the moulding parameters already available within the co-injection system to offer an expanded range of material combinations for multimaterial moulding. Comparisons are made between multimaterial mouldings made with miscible polymers, immiscible polymers with no compatibiliser, and immiscible polymers bonded by compatibilisers.     

Gold Nanolayers on Plasma-Treated Polypropylene

This work deals with characterization of polypropylene (PP) exposed to plasma discharge and gold layers deposited on the plasma modified PP. PP foils were exposed to Ar plasma and subsequently metallized with sputtered Au layer. Chemical structure of the plasma modified PP was studied using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering (RBS). Wettability of the plasma modified PP and its changes during sample aging were determined by goniometry. Surface morphology of PP and deposited Au layers was measured with atomic force microscopy (AFM). Continuity of Au layers was characterized by measuring their sheet resistance. With increasing exposure time in the plasma discharge the water contact angle decreases and the polymer surface becomes more hydrophilic. During the aging of the plasma treated samples the contact angle increases again. Plasma treatment leads to a decrease of the PP surface roughness and to generation of oxygen-containing polar groups on PP surface. During sample aging the concentration of the oxygen-containing groups decreases.     

Effect of processing parameters on structural features of tungsten carbide after electrical discharge machining (EDM)

Abstract

Tungsten carbide (WC) is an extremely hard material which is used extensively in the manufacturing of tools and dies. In the presence of cobalt as a binder its machining becomes a difficult task because of interfacial bonding. In the EDM process, where electrical energy is used for the machining of the substance, the heat generated due to the plasma is responsible for removal of the substance at the interface. The heat generated is conducted differentially because of the composite structure of the tungsten carbide cermet. In order to improve the technological performance it is essential to understand the morphological features of tungsten carbide after machining. The studies have been conducted using different machining parameters. The objective of this study is to analyse the impact of machining parameters on the morphology of tungsten carbide suitable to withstand impact load on press forging for small components during operation. Experiments have been performed with the specially designed fixtures with proper flushing arrangements, to avoid arcing during the process. WC of P20 grade which is one of the most suitable grade substances to withstand load after EDM, has been used as work piece material for the entire study. Copper, graphite and copper tungsten electrodes have been used for the present study. The morphological features were studied with the help of the scanning electron microscope (SEM). It was observed that structural features varied with variation in electrode under similar experimental conditions. Phenomenon of such structures is discussed at length. The formations of cracks on WC have also been studied in detail. The detail of this study is presented in the paper.     

Role of inorganic and theoretical chemistry in ceramics: past,present, and future

Abstract

Theoretical inorganic chemistry has evolved since Professor Mellor's time to include a new generation of quantum mechanics based calculational methods to understand and predict chemical reaction pathways. Semi-empirical molecular orbital (MO) calculations have been used in the fields of glass and silica structure analysis, fracture mechanics, sol–gel processing of net shape optics, porous matrixes for hybrid optics, sensors, and tissue engineering scaffolds. Applications of MO calculations in biomaterials interface reactions, biomimetics, and biomineralisation have also been made. Future directions for use of theoretical inorganic chemistry in the ceramic industry are forecast.     

Oxidation Behavior of ODS Alloy MA 6000

MA 6000 is a mechanically alloyed, Ni-base ODSalloy. Excellent high-temperature strength makes it astrong candidate for application in high-temperatureindustrial processes. In order to assess its usefulness for high-temperature structural components,in-depth knowledge of its oxidation behavior,particularly long-term exposure, is necessary. Thepresent work deals with studies of the cyclic andisothermal oxidation of MA 6000 in the temperature range900-1050°C, with emphasis at 1050°C. A fewcomplementary studies have been carried out on the oxideintegrity under creep conditions for exposure times of up to 11,000 hr. The results have shown thatoxidation of MA 6000 involves rather complex mechanismsand alterations of the oxidation behavior still occurafter long-term exposure. Excellent oxidation resistance is based on the formation of an internalcontinuous Al₂O₃ layer.