Iranian Journal of Materials science and Engineering
Volume:6 Issue: 1, Mar 2009

In this paper, the forming process of a central hub by radial-forward extrusion is analyzed by using the finite element software, ABAQUS. Radial-forward extrusion is used to produce hollow parts that generally feature a central hub with radial protrusions. Effective design factors such as mandrel diameter, die corner radius, die fillet radius, mandrel corner radius, tube wall thickness and frictional conditions on the force required are investigated by simulation process. Commercially pure Aluminum AA1100 is selected as a model material for both experimental investigation and simulation analysis. Comparison is made and good agreement between the experimental result and that of finite element method is achieved.

A combination of mechanical activation and Differential Thermal Analysis (DTA) together with X-Ray Diffraction (XRD), and various microstractural characterization techniques were used to evaluate the starting reaction in the combustion synthesis of TiC-Al2O3 composite in TiO2-Al-C system. The mechanical activation was performed on the mixtures of two components of TiO2/Al, Al/C and TiO2/C and then the third component was added according to the stoichiometric reaction for 3TiC+2Al2O3 composite formation. The powder mixtures were heated up to 1450 °C under Argon atmosphere at a heating rate of 10 °C/min. The combustion synthesis temperature was observed to decrease from 962 °C to 649 °C after milling of TiO2/Al mixture for 16 hr. On the contrary, the mechanical activation of Al/C and TiO2/C mixtures for 16 hr made the reaction temperature increase to 995 °C and 1024 °C, respectively. The decrease in reaction temperature as a result of milling the TiO2/Al mixture could be due to an increase of TiO2 and Al interface area as confirmed by TEM micrographs and XRD patterns of milled powder mixture. In addition, DTA experiments showed that for the sample in which TiO2 and Al were mechanically activated the reaction occurred at the temperature even lower than that of Al melting point.

Nanoparticles exhibit a high reactivity and strong tendency towards agglomeration. In this study, aluminum oxide (alumina) nanoparticles were characterized by gas adsorption (BET), transmition electron microscopy (TEM) and photon correlation spectroscopy (PCS) techniques to assess the agglomeration of the particles. There is a good correlation between the BET and TEM measurements but PCS was larger in the mean and median size and with a degree of agglomerates being detected. Some agglomeration was evident, but most of the particles existed as discrete objects as observed in the (HR) TEM images which were in good agreement with the agglomeration factor.

Due to the expansion of high voltage Alternating Current (AC) power transmission lines and cathodically protected buried pipelines, it is becoming more and more difficult to construct them with enough safe distances between them. Thus, the pipelines are frequently exposed to induced AC interferences, which result in perturbation of Cathodic Protection (CP) due to AC corrosion. To study the above criterion, an experimental set up was used with coupons exposed to simulated soil solutions, while under both CP and AC induced condition for which an AC+DC power supply was utilized. The experiments were carried out in several simulated soil solutions corresponding to several soil samples collected from various regions along a buried pipeline with overhead parallel high voltage power transmission line. The results indicated that AC corrosion depends strongly on the composition of the soil.

Nano- size alumina particles have been synthesized by mechanical activation of a dry powder mixture of AlCl3 and CaO. Mechanical milling of the above raw materials with the conditions adopted in this study resulted in the formation of a mixture consisting of crystalline CaO and amorphous aluminum chlorides phases. There was no sign of chemical reaction occurring during milling stage as evidenced by x-ray diffraction studies. Subsequent heat treatment of the milled powder at 350ºC resulted in the occurrence of displacement reaction and the formation of Al2O3 particles within a water soluble CaCl2 matrix. The effect of higher temperature calcinations on the phase development in this powder mixture was followed by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). Differential thermal analysis (DTA) was used to compare the thermal behavior between the milled and unmilled powders. Perhaps the most important result in this study was the observation of á-Al2O3 phase at a very low temperature of 500ºC.

Formation of a hybrid coating by the use of plasma nitriding and hard chromium electroplating on the surface of H11 hot work tool steel was investigated. Firstly, specimens were plasma nitrided at a temperature of 550 °C for 5 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. Secondly, electroplating was carried out in a solution containing 250 g/L chromic acid and 2.5 g/L sulphuric acid for 1 hour at 60 °C temperature and 60 A/dm2 current density. Thirdly, specimens were plasma nitrided at a temperature of 550 °C for 5 and 10 hours in an atmosphere of 25 vol. % H2: 75 vol. % N2. The obtained coatings have been compared in terms of composition and hardness. The compositions of the coatings have been studied by X-ray diffraction analysis. The surface morphology and elemental analysis was examined by using scanning electron microscopy. The improvement in hardness distribution after third step is discussed in considering the forward and backward diffusion of nitrogen in the chromium interlayer. Also, the formed phases in the hybrid coating were determined to be CrN+Cr2N+Cr+Fe2-3N+Fe4N.

Horizontal continuous casting is widely used to produce semi-finished and finished metallic products. Homogeneity in metallurgical characteristics and mechanical properties in such products is of importance. In the present work microstructure and mechanical properties of a horizontal continuous cast pipe have been studied. Microstructural features were investigated by an optical microscope equipped with image analyzer and SEM was used to characterize precipitates. Tensile behavior, impact strength and hardness variations were the mechanical properties which were studied. Results showed that microstructure and mechanical properties had diversities in different parts of the pipe and distinct differences were observed between upper and lower parts of the pipe. A meaningful correlation was found in microstructure and mechanical properties in different parts of the component.