Iranian Journal of Materials science and Engineering
Volume:14 Issue: 2, Jun 2017

In this work the procedure to the synthesis of Ba2GdSbO6 complex perovskite by the solid-state reaction method is reported. Theoretically a study of the crystalline and electronic structure was performed into the framework of the Density Functional Theory (DFT). The most stable structure is obtained to be a rhombohedral perovskite with a lattice constant a=6,0840 Å. Due the occurrence of a mean energy gap of 2,84 eV close to the Fermi level for both up and down spin polarizations this material is classifies as insulator. The effective magnetic moment of material obtained from the calculations was 7,0 mB. The crystalline structure was analyzed through the X-ray diffraction technique and Rietveld refinement of the experimental data. Results are strongly in agreement with those theoretically predicted. Magnetic response was studied from measurements of magnetic susceptibility as a function of temperature. Results reveal the paramagnetic feature of this material in the temperature regime from 50 K up to 300 K. From the fitting with the Curie law the effective magnetic moment was obtained to be 8,1 mB, which is slightly higher that the theoretical value for the Gd3 isolated cation predicted by the theory of paramagnetism. The energy gap obtained from experiments of diffuse reflectance is relatively in agreement with the theoretical predictions. The dielectric constant as a function of applied frequencies at room temperature was measured. Results reveal a decreasing behavior with a high value of dielectric constant at low applied frequencies.

In this paper the effect of plasma spray parameters, atomizing gas and substrate preheat temperature on microstructure and phase composition of YSZ coatings produced by SPPS process have been investigated. The experimental results showed that increasing the power of plasma, using hydrogen as the precursor atomizing gas and increasing substrate preheat temperature decrease the amount of non-pyrolyzed precursor in the coatings. At low plasma power most of the deposited precursor is in non-pyrolyzed state, and consequently the applied coatings are defective. The increase in substrate temperature beyond 800oC either by preheating or heat transfer from plasma torch to the substrate, prevent the coating formation. In SPPS coating formation, up to a special spray distance the optical microscopy image of the coatings showed a snowy like appearance. XRD analysis showed that in this situation the amount of un-pyrolyzed precursor is low. Beyond this spray distance, spherical particles, are obtained and XRD analysis showed that most of the precursor is in un-pyrolyzed state.

The mechanism of diffusion layer growth in plasma nitrided coatings applied on a St52 steel using an active screen is investigated. The nitriding was performed at 450,500 and 550 ◦C temperature nitriding times of 5, 10 and 15 h, in a gas mixture containing 20 vol. % H2: 80 vol. % N2 and DC-pulsed plasma nitriding unit.
The surface, cross section and the thickness of diffusion of specimens was studied in terms of optical and scanning electron microscopy. According to the measurements of diffusion layer thickness, values of Q and D0 for nitrogen diffusion in substrate were calculated as 50585 (j/mol) and 4.11×10-10 (m2/s)respectively. The variations of depth of hardness during nitriding period was determined.

In this paper, cyclic flaring and sinking (CFS) as a new severe plastic deformation (SPD) method was employed to produce the ultrafine grain (UFG) copper tubes. The extra friction has eliminated in the CFS method that provided the possibility for production of longer UFG tubes compared to the other SPD methods. This process was done periodically to apply more strain and consequently finer grain size and better mechanical properties. The CFS was performed successfully on pure copper tubes up to eleven cycles. Mechanical properties of the initial and processed tubes were extracted from tensile tests in the different cycles. The remarkable increase in strength and decrease in ductility take placed in the CFS-ed tubes. The material flow behavior during CFS processing was analyzed by optical microscopy (OM), and a model was presented for grain refinement mechanism of pure copper based on multiplication and migration of dislocations (MMD). This mechanism caused that the initial grains converts to elongated dislocation cells (subgrains) and then to equiaxed ultrafine grains in the higher cycles. The CFS method refined the microstructure to fine grains with the mean grain size of 1200nm from initial coarse grain size of 40µm.

Indonesian Navy (TNI AL) is the main component for Maritime Security and Defence. Because of that, TNI AL needs Indonesian Warship (KRI) to covered Maritime area. The main requirement from KRI is fulfilled by demand. To pock of fuel demand from KRI at Naval Base, it needs a new pipeline of fuel distribution network system. The pipeline network system used for maximum lifetime must be protected from corrosion. Basically, there are five methods of corrosion control such as change to a more suitable material, modification to the environment, use of protective coating, design modification to the system or component, and the application of cathodic or anodic protection. Cathodic protection for pipeline available in two kinds, namely Sacrifice Anode and Impressed Current Cathodic Protection (ICCP). This paper makes analysis from design of Impressed Current Cathodic Protection and total current requirement in the method. This paper showed both experimental from speciment test and theoritical calculation. The result showed that design of Impressed Current Cathodic Protection on fuel distribution pipeline network system requires voltage 33,759 V(DC), protection current 6,6035 A(DC) by theoritical calculation and 6,544 A(DC) from pipeline specimen test, with 0,25 mpy for corrosion rate. Transformer Rectifier design needs requirements 45 V with 10 A for current. This research result can be made as literature and standardization for Indonesian Navy in designing the Impressed Current Cathodic Protection for fuel distribution pipeline network system.

In this study, carbon nano fibers (CNFs) were mixed into epoxy resin through a magnetic stirrer and again mixed using ultra sonicator. Using hand layup technique, biaxial braided fiber composites were prepared with unfilled, 0.2, 0.5 and 1 wt% CNF. Tensile test and shear test was performed to identify the tensile strength and shear strength of the composites. Fractured surface of the tensile specimens were examined by scanning electron microscopy to identify morphologies of nanoparticles. A discrete three layer model was developed for prediction of the tensile modulus and shear modulus of biaxial braided fiber composites. Theoretical and experimental values were compared. The experimental and theoretical results show that the addition of CNF in the epoxy matrix had significant influences on the mechanical properties of biaxial carbon braided fiber composites. CNF inclusion with braided composite promoted the tensile modulus, tensile strength, shear modulus and shear strength up to 0.5wt% of the biaxial carbon braided fiber composites.

In this research, nanocrystalline Co-Fe coatings were electrodeposited on copper substrate. The influence of current density on different properties of the films at two pH levels was investigated. All the coatings showed nodular structure with rougher morphology at higher current densities. Due to anomalous deposition at higher current density, the amount of iron content increased and reached its maximum value at about 50 wt.% for the coating obtained from pH 5. X-ray diffraction patterns showed hcp structure as the dominant phase. However, by increasing current density at lower pH value, a double phase structure containing fcc藊 phases was detected. It was observed that current density has a positive effect on grain refinement. However, coarser grains would obtain at lower pH value. Microhardness measurements showed that, there is a direct relationship between grain size and microhardness. Moreover, microstructure in double phase structure films can influence microhardness more dominantly. Vibrating sample magnetometer (VSM) measurements indicated that the saturation magnetic is proportion to deposited iron content and reached its maximum value at about 1512 emu/cm3. It was cleared that grain size, phase structure and chemical composition can affect coercivity of the films effectively.

The effects of applied load, sliding speed and sliding distance on the dry sliding wear behavior of aged Al-SiCp-Gr composites were investigated. The specimen were fabricated by stir-casting technique. The pin-on-disc wear testing machine was used to investigate the wear rate by design of experiments based on L27 using Taguchi technique. Sliding distance was the most important variable that influenced the wear rate followed by sliding speed and applied load. The worn out surfaces were analyzed by SEM and EDS to study the subsurface mechanism of wear. The addition of reinforcements showed improved tribological behavior of the composite than base alloy.