Journal of Advanced Materials and Processing
Year:2015 | Volume:3 | Issue:3|Papers Count:7

The influence of the sample size (diameter while keeping the length constant) in equal channel angular pressing (ECAP) of pure aluminum is examined using finite element method (FEM) and experiment. Aluminum rods with different sizes were processed via ECAP and the effect of the sample size on the strain homogeneity, process load, and the ratio of the friction to the total force was evaluated. The results showed that there is no distinct trend in variation of the strain homogeneity when the sample diameter is changed although largest diameter sample exhibits the best strain homogeneity. It was apparent that an increase in the sample diameter caused an increase in the total required load. A decrease in the sample size led to a significant increase in the ratio of the friction to the total force. On the other hand, the friction force is more sensitive than the deformation force to the sample size. More precisely, the friction to total load ratio may be related to the ratio of the sample length to the sample diameter (l/d). In a constant sample length, friction to total load ratio amplifies significantly with a decrease in the sample diameter. The present study showed some limitation for the scaling up of the ECAP process for the industrial application especially with increase in the sample length. It may be concluded that the ECAP processing is not suitable method for producing of long UFG materials.

The TiO2–SiO2 thin films were deposited on the AISI 316L stainless steel via the sol-gel method. Then, the effect of the added amount of SiO2 on the structure, morphology and mechanical properties of the films and corrosion behavior of the AISI 316L stainless steel substrate were investigated Bu using X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, depth-sensing indentation technique supporting micro-scratch mode and potentiodynamic polarization test. It was observed that the appropriate amount of SiO2 addition to the TiO2 film not only decreased the particle size of the TiO2–SiO2 crystal but also could help to improve the surface quality. Mechanical and tribological properties of the films were found to be improved in the range of 10–15%mol of SiO2 addition compared with the pure TiO2. The minimum root mean square value was obtained from the film with a silica content of 10%mol. In addition, the corrosion behavior of the AISI 316L stainless steel was improved by adding 15%mol of SiO2. Under the UV illumination conditions, photo-generated electrons accumulated in this film could perfectly protect the substrate photocathodically.

Zirconium Diboride (ZrB2) powder was synthesized at low temperature via a Direct Molten Salt Reaction (DMSR) method. The influence of different salt compositions including the eutectic mixture of (KF-NaF), (KF-KCl) and (KCl-NaCl) on the morphology and purity of the reaction products was studied. The obtained samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Furthermore, the formation mechanism of ZrB2 was investigated by DTA/TG. The results show that alongside eutectic mixture of chloride salt, the ZrB2 powder can be obtained by eutectic mixture of the fluoride salt. In addition, the obtained ZrB2 powder without additional salt has hexagonal prism morphology, whereas the ZrB2 particles prepared by the eutectic mixture of fluoride salt have higher purity and particle size and hexagonal morphology as well. The synthesized ZrB2 powder in chlorofluoride salt has lower particle size and purity and non-uniform morphology. The synthesized ZrB2 powder is different from the starting material in term of morphology and particle size. Therefore, the dissolution-precipitation mechanism may play a dominant role in the synthesis of ZrB2 during the DMSR process.

Catalytic alkylation of toluene with methanol was carried out over Zr- Cr- and Co- pillared clay catalysts in a catalytic flow system operated under atmospheric pressure at a temperature range of 250-450oC. The pillared clay catalysts were prepared via sonication technique. Results indicated that the pillaring of montmorilonitic clay material with polyoxy-metalic cations (Zr- Cr- and Co-) improves the texture properties and thermal stability of the obtained catalysts. The Co-PILC catalyst is the most active and selective catalyst towards p-xylene formation, i.e. Co-PILC catalyst is a shape selective for p-xylene formation.

In the present paper, the effects of friction stir welding (FSW) tool rotational and traverse speeds on heat generation and temperature distribution in welding zone of AA1100 aluminum alloy and A441 AISI joint were studied. Computational fluid dynamics method was used to simulate the process with commercial CFD Fluent 6.4 package. To enhance the accuracy of simulation in this study, the welding line in the work-pieces interface was defined with pseudo melt behavior around the FSW pin tool. Simulation results showed that with increase of the FSW tool rotational speed, more heat was generated heat and the dimensions of the stir zone were enlarged. The calculation results showed that maximum temperature occurred on the advancing side. Moreover, with increasing tool linear speeds the heat generation experienced a downward growth trend. With increasing the traveling speeds the time to reach maximum temperature in the stir zone increased, but the tool rotational speed had no effect on the time to reach maximum temperature. The model outcomes showed that more than 85% of total heat was produced by tool shoulder and that the maximum heat with the selected parameters was 935 kelvin degrees. The computed results showed that the maximum value of strain rate achieved was 29 S-1 for the A441 AISI and 42 S-1 at the AA1100 side.

Due to their high hardness and wear resistance, electro less nickel-boron (Ni-B) coatings have found numerous applications. In the present study, the influence of the heating rate on the morphological features of oxidized electro less Ni-B coatings was investigated. The oxidation behavior of electro less coating layers was studied by TGA method under non-isothermal conditions at the heating rates of 5, 9 and 13°C/min. The phase compositions, elemental constituents, and microstructural characteristics were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM), respectively. Results showed that the morphological features of the oxidized coating were significantly influenced by the heating rate so that under the heating rate of 5oC/min the morphology of the oxidized layer was a porous film with an average pore size of around 2 mm. With increasing the heating rate to 9oC/min, more recessed pores or intervals were gradually overlaid by a film. Further increasing the heating rate to 13oC/min caused the formation of polygonal protuberances on the surface.

In this work, structural and magnetic properties of the LaMnO3+d compound prepared by citrate precursor method and annealed in the presence of oxygen are investigated. The structural characterization of LaMnO3+ d by X-ray powder diffraction and X’pert package and Fullprof program provides evidence for a rhombohedral structure (R-3c space group) confirmed by FTIR measurement as well. The magnetic measurements show a super-paramagnetic behavior of LaMnO3+d due to low values of the coercive field and remanance magnetization and also high value of saturation magnetization. In addition, a comparative study of the crystallite size of the compounds obtained from powder XRD is reported. The Williamson-Hall analysis, size-strain plot and Halder-Wagner methods were used to study the individual contributions of the crystallite sizes and lattice micro-strain to isotropic line broadening of all the reflection peaks of the LaMnO3+d compound. The results show that the Halder-Wagner method is more accurate, with all data points touching the fitting line better than in the other methods. The crystallite sizes estimated from XRD (30.86 nm) and particle size estimated from TEM method (36 nm) and also the magnetic core size (33.6 nm) estimated from magnetic measurement are in good agreement, while a little difference reflects a spherical shape of the nanoparticles.