مجله مواد نوین
سال دوم شماره 2 (پیاپی 6، زمستان 1390)

In this study, friction stir welding (FSW) was used for joining AL-1100 to AZ31. In the rotation speed between 400 to 800rpm and travel speed between 15 to 30mm/min, in the condition that stirring pin was inserted in Mg side of weld, friction stir welded samples without any defect were made. In high rotation speed, intermetallic compounds were seen in the XRD results of the stir zone. The best tensile strength, about 122MPa, was reached in rotation speed of 570rpm and travel speed of 20mm/min.

In present research, the influence of input parameters in induction hardening process (power, current, induction time and, the gap between inductor's coil and crankshaft) on metallurgical structure changes, depth of hardened layer and magnitude of surface hardness has been investigated. The results suggest a direct relationship between power and current induction time, with depth of hardened layer and surface hardness. The results show that with increase of power and current induction time, surface hardness is increased. Also, with increase of gap between coil and crankshaft, it was observed that the width of hardened zone declines.

In the present study a new electroplating bath for the deposition of Ni-Zn-P nickel-based alloy coatings and Ni-Zn-P/nano SiC nickel-based nanocomposite coatings on low carbon steel substrates was introduced. The optimum bath composition was found through comparing the amount of coating cracks taken by SEM. Also a comparison between the corrosion behavior of alloy coatings obtained from bath with different concentrations of phosphoric acid and nano composite coating in 3.5%wt NaCl solution was investigated using tofel and impedance curves.

Equal channel angular pressing (ECAP) is considered to be the most promising severe plastic deformation route to receive ultrafine grained materials with high strength and good physical properties. Mechanical properties, electrical conductivity and electrical erosion of commercial pure copper rod processed by ECAP were investigated. For this purpose a set of ECAP dies with the intersecting channel angle of 90 and an external arc of curvature of 37º and punch was design and manufactured. Commercially pure copper was processed through ECAP die up to 8 passes. The mechanical experiments indicated that the yield stress increased with increasing the number of passes till the 5th one, but beyond this pass a little decrease was observed. The trend of electrical conductivity changes is different from the yield stress of the material, in a way that electrical conductivity will gradually decrease to the fifth passes. After which electrical conductivity will increase slightly. Also for the first time electrical erosion of pure copper processed by ECAP during the electrical discharge processes were investigated. It was found that, with increasing the number of passes and finer grains of pure copper, electrical erosion decrease with respect to NON-ECAP copper in the same testing conditions.

The aim of the present research was to optimize practical conditions of the sol-gel synthesis of silica nanoparticles. In so doing, silica particles were synthesized using sol-gel method and their size and morphology were investigated by use of SEM and TEM images. The effect of changing the mole ratio of reactive comparents, acids and silica pre-matter, acid type and different silica pre-matter used on morphology and the size of products was investigated by using SEM and TEM. The reaction time was studied as a very important factor in products’ digestion phase which plays a significant role in determining particles’ size and rate of cracking products. Finally, optimized conditions to produce 50-80 nm diameter nanostructures silica were reported. These products can be used as drug delivery systems.

The corrosion inhibition of plain carbon steel was studied by using an imidazoline derivative as an inhibitor and iodide ions additive in CO2-saturated 3% NaCl solution with potentiodynamic technique in Tafel region. The experimental results revealed that the imidazoline derivative inhibited the corrosion of steel and the extent of its inhibition was concentration dependent. The results of potentiodynamic polarization investigations revealed that imidazoline functioning as a mixed inhibitor showing anodic and cathodic behavior. Also, it was resulted that the inhibition efficiency of imidazoline was enhanced by addition of iodide ions due to synergistic effect and the synergism parameter was found to be greater than unity. Furthermore, the adsorption of imidazoline derivative on the steel surface followed the Langmuir adsorption isotherm and it was chemically adsorbed on the surface of the steel. The surface morphology was investigated by a scanning electron microscope and the result showed the formation of a protective surface film. Also it was found that surface roughness decreased after addition of inhibitor and iodide ions.

In this research, the effects of plasma nitriding parameters including frequency and duty cycle were investigated on samples with different grooves in the two method conventional plasma nitrided (CPN) and active screen plasma nitrided (ASPN). The samples with thicknesses of the grooves of 2, 4, 6, 8 and 10 mm were nitrided under the atmosphere content of 75%H2-25%N2, The temperature of 500, the duty cycles of 40%, 60%, 80%, and the frequencies of 8, 10 kHz for 5 hours. Then the properties of the nitrided samples were investigated by SEM, XRD, Micro Hardness, and Roughness measurements. The results of the experiments indicated that with increasing frequency, the duty cycle, and the thickness of the grooves, the roughness of the surfaces increased in both methods. Hallow cathode effect occurred at the sample with 2 mm width groove, in the CPN method, leading to the overheating of the sample. The surface morphology of the CPN treated samples consists of cauliflower shape surface nitrides while the surface of the ASPN samples are covered by the hexagonal particles with uniform distribution. Also, it was found that, the compound layer of the treated samples in two method nitriding consisted of ´γ: Fe4N and ε: Fe2-3N phases.

Castable refractories are widely used in sever conditions at high temperature and pressure applications such as Petro Chemical process, industrial furnaces and specially in iron and steel industries. Attemps were made to improve the quality of the refractory castables by reducing cement content and/or by using different additives. In the present study the influence of zircon addition on phase analysis, microstructure and properties of ultra low cement in situ spinel castable refractory has been studied. Materials such as tabular alumina as the aggrigate, reactive alumina, deadburn magnesia, and micro silica as the fillers, and zircon as additive were used in this research. In situ spinel formation and influence of zircon addition on the phase developments were investigated by XRD analysis. Samples fired at 1400 ºC and 1600 ºC for 2 hours. Results showed improved physical and mechanical properties by addition of 2, 4, 6%, Zircon to the samples. Results also showed zircon decomposition has started at about 1400ºC and completed at 1600 ºC, resulting a reaction between zircon and alumina to form ZrO2 and alomiosilicate(Kyanite) composite in the matrix of the refractory castable samples. Finally in the samples fired at 1600°C extremely high cold crush strength (above 12 MPa) was detected which may be related to the spinel and kyanite formation in the matrix.