Journal of advanced materials and processing
Volume:2 Issue: 1, Winter 2014

Tubular channel angular pressing (TCAP) is a recently invented novel severe plastic deformation technique for producing UFG tubes. Plastic deformation analysis using the finite element method (FEM) was carried out to investigate the effects of trapezoidal channel geometry on strain inhomogeneity index (SII), strain level and required load compared to previously used channel geometries. The results showed that SII is decreased to 0.003 in the case of trapezoidal channel while they are 0.13 and 0.24 in the cases of semicircular and triangular channel types, respectively. It means that excellent strain homogeneity is achieved in TCAP processing using trapezoidal channel geometry. The required load for the trapezoidal channel was 41% lower than that for the triangular channel but it is almost the same for semicircular channel. From the point of view of better strain homogeneity and needing lower process load, TCAP processing using trapezoidal channel is an excellent technique for producing UFG tubes.

Among one dimensional nanomaterials, TiO2 nanorods have found important applications in various industries due to optical, photocatalyst and self-cleaning properties. In this research, at first TiO2 nanorods were synthesized on a glass substrate by hydrothermal method. Then a thin film of TiO2 particles was dip coated (as seed layer) on the substrate. After that, hydrothermal synthesis of TiO2 nanorods with 0.05 and 0.1 mol concentrations was carried out on the seed layer. Morphology and microstructure of the seed layer and nanorods were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Hydrophobicity of nanorods was studied by contact angle instrument. Results revealed that nanorods synthesized on the glass substrate without seed layer are not aligned at all and have the average diameter of 120 nm, whereas nanorods synthesized on the seed layer are well-aligned with 30nm average diameter. The result obtained from contact angle instrument showed that nanorods synthesized with 0.05mol concentration have larger contact angle (157º), compared to those synthesized with 0.1mol concentration which have 115º contact angle.

One-dimensional (1D) undoped and Cr doped ZnO nanorods with average length of 1 µm and diameter of 80 nm were synthesized using hydrothermal method where a fast growth of ZnO nanorods on the seed layer was observed. Afterwards, the effects of Cr dopant on structural, surface morphology and optical properties of nanorods were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultra-violet visible (UV-Vis) spectroscopy. The results showed that ZnO has a wurtzite hexagonal structure and that the Cr atoms were well incorporated into the ZnO crystal structure. Moreover, it was found that the Cr atoms could facilitate the preferential growth of nanorods in C-axis. Also, it was concluded from optical properties that doped ZnO nanorods was so appropriate for photocatalytic applications because the optical band gap. For example, the calculated band gap of ZnO nanorod decreased from 3.12 eV for pure ZnO nanorods to about 2.41eV for 3 at. % Cr doped ZnO nanorods which is quite enough to be activated even at visible (550nm) light for photocatalyst aims.

Homogeneous distribution of mullite in the matrix of alumina can be obtained through sol-gel method. In this work, nanopowder of alumina-mullite composite was synthesized with high homogeneity and high purity. So aluminum chloride hexahydrate and tetraethyl orthosilicate were used instead of alumina or mullite nanopowder. Studying the simultaneouse thermal analysis (STA) of mullite precursor reveals two endothermic peaks at 145 and 240°C due to dehydration and removal of the molecular water and the chloride component. An exothermic peak is also detected at 855°C. According to the XRD patterns of alumina-15vol.% mullite precursors calcined at different temperatures, crystallization of transitional alumina phases (γ, κ) occurs approximately at 800°C. Then these phases transform to α alumina approximately at 1000°C. XRD patterns of alumina-15%vol. mullite which were calcined at different temperatures show peaks of mullite relating to 1000°C. The specific surface area of this nanopowder calcined at 900°C was calculated to be 120.9±0.5 m2/g. The nanopowder was observed by TEM.

Ultra-fine grained (UFG) structure (~0.6 µm) was produced in the stir zone (SZ) of 6061-T6 aluminum alloy joints using friction stir processing (FSP) cooled by liquid nitrogen (N2). A new experimental set-up was used to simultaneously quench the lower and upper surfaces of the samples during the processing. In addition, FSPed joints, using a steel backing plate, were produced at room temperature as a reference. Sub-structural studies have been carried out to investigate the occurrence of dynamic recrystallization and grain growth in the weld area of the samples. The results indicate that the microstructure was not fully recrystallized as a high dislocation density (3.5×1014 m-2) was measured in the stir zone (SZ) of rapidly cooled joints in compare with that of the air-cooled joints (1.5×1014 m-2). Moreover, the rapid cooling generated a very high dislocation density of about 6.5×1014 m-2 in the thermo-mechanical affected zone (TMAZ). Accordingly, better mechanical properties were obtained in the SZ. In contrast, lower strain hardening capacity and hardening exponent values were obtained in the rapidly cooled joints where the highest fraction of low angle grain boundaries (LAGBs) and largest number of dislocations were measured.

Equal channel angular pressing is the most promising method of severe plastic deformation with the capability of producing ultrafine grained materials. These materials exhibit improved mechanical and physical properties compared with their coarse grained counter parts.The temperature variation in the sample during ECA-pressing is a key factor determining the final microstructure and mechanical properties of processed material. Therefore, in the present study, temperature rise and temperature distribution in the sample was studied with the aid of finite element simulation. In this regard, the effect of friction, ram speed and material type on the amount of temperature rise and also the temperature profile in the sample was investigated. Results of FEM simulations showed good consistency with the temperature data acquired in the experimental work. In addition, it was shown that the sample temperature AND THE AMOUNT OF TEMPERATURE RISE increases with the increase of friction; ram speed and work hardening coefficient of the material.

One of the attractive low activation steels is the austenitic Mn-Cr steel from the view point of waste disposal because of few long-lived nuclides. In this paper, three types of Mn-Cr austenitic steels were fabricated by vacuum induction furnace. Then plates with 10 mm thickness were fabricated by hot-rolling. The physical metallurgy of these steels was studied by the corrected Schaeffler diagram, X-ray and electron diffraction patterns. The corrected Schaeffler diagram and X-ray diffraction (XRD) results have shown that the matrix of these steels is a single γ-phase structure. Also, the corrosion behaviour in 0.1M HCl solution was evaluated by open-circuit potential, Tafel polarization, and electrochemical impedance spectroscopy (EIS). The results of Tafel polarization experiments show corrosion current density of all three Cr-Mn steels is in the range of 10-4 A cm-2 which indicates their appropriate resistance in this acidic environment. The Nyquist plots showed that polarization resistance from the first to third Cr-Mn steels decreases. This trend is due to increase in corrosion current density which corresponds to Tafel polarization curves.