نشریه مهندسی متالورژی و مواد
سال سی و پنجم شماره 1 (بهار 1403)

In this study, the effect of Al-30Er grain refiners, extrusion and heat treatment conditions on an Al-3Mg-2.5Cu aluminum alloy was studied. Different amounts of Al-30Er (0.5 wt.% Er, 1 wt..0% Er, 1.5 wt.% Er and 2 wt.% Er) were added to the molten alloy at 750 ◦C. The optimum level of Er was found to be 1 wt.%. Microstructural examinations and fracture surfaces were conducted by scanning electron microscopy coupled with an energy dispersive spectrometry. T6 heat treatment including quenching to room temperature and aging at 120 C for 24 h was employed to reach to the maximum strength. In order to eliminate the porosity inside the samples and improve the strength of the samples, the extrusion process was used with a ratio of 6 to 1. For the prototypes in the direction of extrusion, the diameter of the primary cylinder is 29 mm. By adding grain refiners and applying T6 heat treatment and extrusion process, a significant improvement in mechanical properties was achieved. The average ultimate tensile strength (UTS) of the samples before and after T6 heat treatment and extrusion process increased from 225 MPa to 602 MPa. Addition of one percent by weight of Er, applying heat treatment and extrusion process, caused a 167% improvement in tensile strength compared to the base aluminum alloy.

In this article, the effect of ion type on the transport properties of the structures whose common phases were created by the tantalum-based ion bombardment process has been investigated. The nitrogen ions used in the ion seeding process are considered with an energy of 30 kV and in different doses at ambient temperature. To study the morphology of the surfaces of ion bombarded thin layers, atomic force microscope (AFM) analysis was used and the amount Average roughness is determined. The results show that the common seasons produced by nitrogen ion bombardment have more effects on the transport characteristics. Also, the peak-to-valley ratio decreases. In addition, with the increase of the nitrogen ion dose, the current density has decreased as a function of the voltage, although this decrease is a direct result of the dispersion caused by the existence of unevenness, but the process of this decrease does not follow a specific order for different doses, example sample number one indicates a higher probability of passing. The results show that determining the amount of dose plays an important role in determining the amount of transport characteristics through uneven thin layers.

Due to effects of the gating ratio on the amount of shrinkage porosities and thereby on mechanical properties of steel components, optimizing the gating system is one of the interested fields for scientists focused on the casting industry. In this paper, the casting of a steel centrifugal pump body has been simulated and influences of the gating ratio on the casting quality of the obtained component have been evaluated. Investigated parameters involve the place of formed hot-spots, the speed of the liquid flowing from gates and its uniformity. The obtained results show that in the case of the evaluated component, both of the suggested gating ratios of 2:1.15 and 1:3:3 can distribute the melt well in such a way that the last solidified parts are far from the portions experiencing high stresses during the service. However, using the gating ratio of 1:2:1.5 lets that the sprue to be full of the liquid metal. So, the sprue can compensate the occurred shrinkage and almost prevent the entrance of the out gases. Moreover, it was observed that the symmetry of gates with respect to each other does not have an important effect but with respect to the position of the sprue has a crucial role to ensure a similar speed and behavior of the metal flowing in the different gates.

Impact behavior of cold rolled AA6061 and AA 7020 aluminum alloys were investigated by Charpy impact test. Four longitudinal and long transverse and short transverse (in two groove positions) were studied. The groove angles were 30, 45, 60 and 90 degrees and temperatures tests were dry ice, zero degrees, ambient and boiling water temperatures. Two samples of each variable were taken to ensure the distribution range. Also for strengthening of aluminum alloys T65 precipitation hardening heat treatment was used. The results showed that increasing temperature increased the amount of impact energy and impact energy value decreased with increasing groove angle and failure mode altered from shear to flat and a mixture of both. Samples had the minimum amount of impact energy in the rolling longitudinal direction and the maximum amount of impact energy in the short transverse direction. About 85% of consumed aluminum are processed products such as cold rolled plates, which use casting ingots as a raw material and turn into the final product with subsequent processes, and during these processes, the microstructure also changes.

Tungsten/tungsten nitride bilayer with amorphous structure was deposited on the silicon / silicon oxide substrate by high vacuum thermal evaporation method. To investigate the thermal stability of this bilayer as a diffusion barrier layer, the Cu/W /WN/SiO2/Si multilayer was heated at different temperatures and the results were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and four-point probe (FPP) methods. According to the XRD results, formation of the cupper silicide at 800° C indicates diffusion of copper from the W/WN bilayer in the Si. The formation of a Cu3Si with insulation phase leads to a sudden increase in electrical resistance (212 Ω /cm2) and will disrupt the performance of the W/WN barrier layer as a diffusion barrier. The diffusion of copper into silicon is often through undesirable grain boundaries that occur during the heating treatment of the W/ WN bilayer by changing its phase from amorphous to polycrystalline and shown in X-ray diffraction results. At high temperatures, the electron microscope image has shown fracture, cracking and flaking of the surface of the copper layer, which is caused by thermal stress between the penetration barrier/copper surfaces or the volume of the layers.

In the present research, nanoparticles based on the alumina-yttria system were synthesized using a sol-gel method. Then, the effect of heat treatment on the phase evolution and crystallite size in this composite system was investigated. The produced composite powder was characterized using X-ray diffraction and scanning electron microscopy. Scherrer equation was used to investigate the effect of temperature on crystallite sizes. The composite powder was cold isostatically pressed and subjected to a pressureless sintering process at different temperatures to evaluate its density changes. The X-ray diffraction results showed that the powder sample was initially amorphous. By increasing the temperature, the components of this composite system reacted and Alpha-Al2O3 and Y3Al5O12 phases are formed. The crystallite size of the Theta-alumina phase grew with increasing temperatures up to 1000 C. At higher temperatures, crystallite size decreased due to the decomposition of theta-alumina. The density of the samples increased by increasing the temperature up to 1600 C so that the samples reached a relative density of about 96%. The densification curve of the composite showed three different stages during sintering. Examining the hardness of the samples showed that the hardness increases with the increase of the sintering temperature, and in the sample sintered at 1600 C for 3 hours, the Vickers hardness reached about 14 GPa.