Key Engineering Materials Vols. 510-511

Abstract: Nanostructured multiferroic BiFeO₃ (BFO) powders were synthesized by using the co-precipitation method. Calcination of acquired powder was carried out at 400°C for 3h. Uniaxially pressed pellets were sintered at 500°C, 600°C, 700°C and 800°C for 2 hours in air. These samples were characterized for structural, thermal, electrical and magnetic properties. X-ray diffraction (XRD) confirmed the amorphous nature of the as driven powder and phase purity of the calcined BFO sample. The crystallite size varied with the sintering temperature from 52 to 70 nm. Sintering above 500°C induced impure phases due to oxygen vacancies and volumetric strain in crystal structure. Ferroelectric to paraelectric transition temperature T_C~815°C was verified by the differential scanning calorimetry (DSC). Surface morphology and grain growth was observed using scanning electron microscopy (SEM). Electrical ac measurements were performed in the frequency range from 20 Hz to 3 MHz at room temperature. For a particular sample, capacitance decreased and susceptance increased with the increase of applied frequency signal. These parameters were increased with the increase of sintering temperature. Vibrating sample magnetometer (VSM) revealed the diverse weak ferromagnetic behavior for the samples sintered at different temperatures. Maximum coercivity (Hc~119.2 Oe) and maximum remnant magnetization (M_R~2.1x10^-3 emu/g) were obtained for the sample sintered at 700°C for 2hr.

Abstract: Aluminum and its alloys solidify in large grains columnar structure which tends to reduce their mechanical behaviour and surface quality. Therefore, they are industrially grain refined by titanium or titanium + boron. Furthermore, aluminum oxidizes in ordinary atmosphere which makes its weldability difficult and weak. Therefore, it is anticipated that the effect of addition of zirconium at a weight percentages of 0.1% (which proved to be an effective grain refiner on the weldability of aluminum grain refined by Ti) is worthwhile investigating. This formed the objective of this research work. In this paper, the effect of zirconium addition at a weight percentage of 0.1%, which corresponds to the peritctic limit on the aluminum-zirconium phase diagram, on the weldability of aluminum grain refined by Ti is investigated. Rolled sheets of commercially pure aluminum, Al grain refined Ti of 3 mm thickness were welded together using Gas Tungsten Arc Welding method (GTAW), formerly known as TIG. A constant air gap was maintained at a constant current level, 30 ampere AC, was used because it removes the oxides of the welding process under the same process parameters. Metallographic examination of weldments of the different combinations of aluminum and its microalloys at the heat affected zone, HAZ, and base metal was carried out and examined for width, porosity, cracks and microhardness. It was found that grain refining of commercially pure aluminum by Ti resulted in enhancement of its weldability. Similarly, addition of zirconium to Al grain refined by Ti resulted in further enhancement of the weldment. Photomicrographs of the HAZ regions are presented and discussed.

Abstract: Thermal barrier coatings (TBCs) are multilayered coatings having the complex structure. In thermal spray coatings characteristic features of deposited molten particle and its microstructure is very important in defining coating properties. In this work stainless steel (AISI 316) was used as substrate material on which bond coat of Ni-20Cr and top coat of CaZrO₃ were deposited by air plasma spraying method. Effect of isothermal treatment on the internal microstructure structure of lamella (splat) and phase changes in CaZrO₃ coating was studied. The fractured surface of coatings was investigated to observe the splat morphology. It was observed that the nanocrystallites present within the splat grew with increase in temperature. Further, the monoclinic phase was formed as function of temperature and time.

Abstract: Magnesium hydride (MgH₂) is considered to be a promising hydrogen storage material because of its high gravimetric and volumetric storage capacities. However, its slow kinetics and high desorption temperature (> 300 °C) limit the practical applications. We have selected TiC nanoparticles to modify the hydrogen storage properties of MgH₂. First, Mg nanoparticles were synthesized by thermal desorption of bipyridyl complex of Mg and then MgH₂ nanoparticles were obtained by hydriding the Mg nanoparticles. Composite mixtures (MgH₂ + TiC) were prepared using high-energy ball milling. Structural analysis, morphology and particle size were investigated by X-rays diffractometer (XRD) and scanning electron microscopy (SEM) respectively. Hydrogen desorption properties of MgH₂ was investigated with various amount of TiC nanocatalyst using differential scanning calorimetry (DSC) and seivertz type apparatus (PCT). Desorption kinetics were also studied by pressure composition isotherm (PCI). Results show that the product reveals good reversible hydrogen absorption-desorption cycles even at >150 °C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH₂ could be understood by a modified first-order reaction model, in which the surface condition was taken into account.

Abstract: Comparison of analytical results with finite element results for analysis of isotropic material multicell beams subjected to free torsion case is the main idea of this paper. Progress in the fundamentals and applications of advanced materials and their processing technologies involves costly experiments and prototype testing for reliability. The software development for design analysis of structures with advanced materials is a low cost but challenging research. Multicell beams have important industrial applications in the aerospace and automotive sectors. This paper explains software development to test different materials in design of a multicell beam. Objective of this paper is to compute the torsional loading of multicell beams of isotropic materials for safe design in both symmetrical and asymmetrical geometries. Software has been developed in Microsoft Visual Basic. Distribution of Saint Venant shear flows, shear stresses, factors of safety, volume, mass, weight, twist, polar moment of inertia and aspect ratio for free torsion in multicell beam have been calculated using this software. The software works on four algorithms, these are, Specific geometry algorithm, material selection algorithm, factor of safety algorithm and global algorithm. User can specify new materials analytically, or choose a pre-defined material from the list, which includes, plain carbon steels, low alloy steels, stainless steels, cast irons, aluminum alloys, copper alloys, magnesium alloys, titanium alloys, precious metals and refractory metals. Although this software is restricted to multicell beam comprising of three cells, however future versions can have ability to address more complicated shapes and cases of multicell beams. Software also describes nomenclature and mathematical formulas applied to help user understand the theoretical background. User can specify geometry of multicell beam for three rectangular cells. Software computes shear flows, shear stresses, safety factors etc in all members of three cell beam, analyzes safety of proposed design and provides output with highlighted comments and graphics, in cases where safety factor in any element of multicell beam falls below 1.5. Results of this software were compared and verified with analytical calculations and Microsoft Excel spreadsheet. Development and use of this software provides an easy to use tool, for quick verification of different design cases in three cell beams composed of advanced isotropic materials. Furthermore, the methodology proposed is also useful for similar cases of research in reliable design studies and material analysis.

Abstract: Developing a new engineering material product or changing an existing one requires new design selecting material and choosing appropriate and economical manufacturing processes. These three main factors play a great role on the performance of the product in service. These items are independent and should not be performed in isolation from each other. With the great advancement of technology in the last decade and with the greater number of engineering materials which are now available, together with the increasing pressure to produce more economic and get reliable products an integrated approach which considers design, material selection and the appropriate manufacturing process makes it easier to achieve the optimum product that combines the functional requirements with the reliability at competitive cost. These diverse activities or items are interdependent; therefore should not be considered in isolation from each other, for example, it is not sufficient that design of the product should satisfy the technical, safety and legal requirements, it must also be possible to be manufactured economically and to be sold at a competitive price and easily disposed at the end of its working life cycle. In this paper, the interaction of these items together in order to arrive to the optimum solution for a particular application are given and discussed.

Abstract: Anisotropic (Fe-24Co-15Ni-7.5Al-3Cu-0.3Ti) permanent magnets were prepared by alloy casting technique. Samples were characterized for structural, microstructural and magnetic properties using x-ray diffractrometer (XRD), Scanning electron microscope (SEM) equiped with energy dispersive x-ray spectrometer and DC magnetometer. There is a relation between metallurgical structure and magnetic properties. The magnetic properties of this type of alloy depend on heat-treatment that is controlling the cooling rate in the presence of magnetic field and double aging. How magnetic properties vary with heat treatment is discussed in this work. XRD studied revealed that the alloy was single phase (bcc) with (110) as the major crystallographic plane. Optical and SEM micrographs showed the presence of (Ti,S)-rich precipitates which are randomly distributed in the matrix. Their composition was analyzed by EDX analysis.

Abstract: Presented results report some of the findings of a detailed failure analysis carried out on a main rotor hub assembly, which had symptoms of burning and mechanical damage. The analysis suggests environmental degradation of the grease which causes pitting on bearing-balls. The consequent inefficient lubrication raises the temperature which leads to the smearing of cage material (brass) on the bearing-balls and ultimately causes the failure. The analysis has been supported by the microstructural studies, thermal analysis and micro-hardness testing performed on the affected main rotor bearing parts.

Abstract: Mustard Methyl Esters (further biodiesel) and regular diesel fuel were tested in direct injection diesel engine. Analysis of experimental data was supported by an analysis of fuel injection and combustion characteristics. Engine fuelled with biodiesel had increased brake specific fuel consumption, reduced nitrogen oxides emission and smoke opacity, moderate increase in carbon monoxide emission with essentially unchanged unburned hydrocarbons emission. Increase in fuel consumption was attributed to lesser heating value of biodiesel and partially to decreased fuel conversion efficiency. Analysis of combustion characteristics revealed earlier start of injection and shorter ignition delay period of biodiesel. Resulting decrease in maximum rate of heat release and cylinder pressure was the most probable reason for reduced emission of nitrogen oxides. Analysis of combustion characteristics also showed that cetane index determined by ASTM Method D976 is not a proper measure of ignition quality of biodiesel. Conclusion was made on applicability of mustard oil as a source for commercial production of biodiesel in Pakistan. Potentialities of on improving combustion and emissions characteristics of diesel engine by reformulating biodiesel were discussed.

Abstract: This work reports on the fabrication and investigation of pressure sensor based on Ag/Cu₂O-PEPC-NiPc/Al composite. The active layer of the composite was deposited by drop-casting of the blend Cu₂O-PEPC-NiPc on flexible substrate. The thin film of the blend consist of cuprous oxide (Cu₂O) micropowder, (5 wt. %), poly-N-epoxypropylcarbazole (PEPC), (2 wt. %) and nickel phthalocyanine (NiPc) micropowder, (3 wt. %) in benzol (1 ml). The film thickness of the composite is in the range of 20-30 μm. It is found that the fabricated sensor is sensitive to pressure and showed good repeatability. The decrease in resistance of the sensor is observed 10 times by increasing the external uniaxial pressure up to 11.7 kNm^-2. The experimentally obtained results are compared with the simulated results and showed reasonable agreement with each other.