Iranian Journal of Materials science and Engineering
Volume:12 Issue: 4, Dec 2015

Different volume fractions (1.3, 2.6, and 7.6 Vol.%) of carbon nanotubes (CNTs) were dispersed within 8Y-TZP nanopowders. Mixed powder specimens were subsequently processed by spark plasma sintering (SPS) and effects of CNTs on the sintering process of 8Y-TZP/CNT composites was studied. Maintenance of CNTs through the SPS process was confirmed using TEM and Raman Spectroscopy. Studies on the sintering profile of zirconia-CNT composites (Z-xC composites) could, to some extent, clarify the effect of CNTs’ volume fraction on the densification rates of Z-xC composites. The specimen with the highest content of CNT (Z-7.6C) showed the lowest sintering rate while it was unable to reach full density.

A comparing study on formation and microstructure features of aluminum titanate is investigated through both solid-state and sol-gel processes. Aluminum titanate formed by firing at 1350ºC and 1450ºC for 4h in solid-state process. In the sol-gel process formation of submicron sized particles is followed by addition of sucrose into the transparent sol. XRD analysis was confirmed the formation of aluminum titanate at 1400ºC in lower duration of calcination (3h) without any additives in the sol-gel process. In this work 2wt% MgO is added to the samples as the additive for forming acceleration of aluminum titanate. The influence of MgO addition and heat treatment are studied on phase formation and microstructure development of aluminum titanate in both procedures. Additive optimizes aluminum titanate formation at lower temperatures (1300-1350ºC). Phase and microstructure studies of Mg containing samples optimally show significance in aluminum titanate formation.

In this paper, polycrystalline pure zinc oxide nano structured thin films were deposited on two kinds of single crystal and polycrystalline of p and n type Si in three different substrate temperatures of 300, 400 and 500◦C by low cost APCVD method. Structural, electrical and optical properties of these thin films were characterized by X ray diffraction, two point probe method and UV visible spectrophotometer respectively. IV measurements of these heterojunctions showed that turn on voltage and series resistance will increase with increasing substrate temperature in polycrystalline Si, while in single crystal Si, turn on voltage will decrease. Although they are acceptable diodes, their efficiency as a heterojunction solar cell are so low.

Creep age forming (CAF) is one of the novel methods in aerospace industry that has been used to manufacture components of panels with improved mechanical properties and reduced fabrication cost. CAF is a combined age-hardening and stress-relaxation that are responsible for strengthening and forming, respectively. This paper deals with the experimental investigations of mechanical and springback properties of Al-Zn-Mg Al alloy in creep forming process. Creep forming experiments have been performed at temperatures of 120◦C and 180◦C for 6–72 h. Results indicated that yield stress and hardness of creep age formed specimens increased with increasing forming time and temperature, simultaneously induced deflection by stress-relaxation increased. Incorporating spring back and mechanical properties, it can be found that the appropriate forming cycle was 180 ◦C/24 h among all forming conditions. CAF Time increase to a certain extent increased mechanical properties. This can be attributed to presence of stress in CAF that causes the precipitates be finer because of creation more nucleation sites. Therefor the growth of precipitates, takes place at long time and postpones the decreasing of the yield stress.

The electrochemical behavior of 6063 aluminum alloy in ethylene glycol-water mixture was investigated by polarization curves and AC impedance measurements (EIS). The results obtained from polarization curves showed that corrosion rate decreased with increasing ethylene glycol concentration. EIS data showed the decrease in the interface capacitance which caused by adsorption of ethylene glycol at the surface of aluminum alloy. The cathodic current increased with the increase in rotating speeds of solution and the anodic current decreased. The effect of temperature was studied and the corrosion rate was increased with increasing the temperature. In addition, thermodynamic parameters were calculated in different ethylene glycol concentrations.

In this study, the composite material with composition of MgH2-5 wt% SiC has been prepared by co-milling of MgH2 with SiC powder. The effect of milling time and additive on MgH2 structure, i.e. crystallite size, lattice strain, particle size and specific surface area, and also hydrogen desorption properties of obtained composite was evaluated by thermal analyzer method and compared with pure un-milled MgH2. The phase constituents and grain size of powder were characterized by X-ray diffractometry method. It has been shown that addition of 5 wt% SiC to MgH2 and mechanical alloying up to 30 h formed a nanocrystalline composite with the average crystallite size of 12 nm, average particle size of 0.5 µm and specific surface area of 10 m2/g. On the other hand, SiC can help to break up particles and reduce the particle size. As a consequence, the desorption temperature of composite material milled for 30 h has decreased from 435 °C to 361 °C.

The purpose of this research is to achieve the optimal parameters for producing forged aluminium alloy 7075 aircraft door bracket by using finite element modelling (FEM) with commercial DEFORM-3D V6.1 and physical simulations with plasticine and Plexiglas dies. Also, forging speed has been examined as the main factor for controlling to produce a part without any defects. The results of Physical Simulation showed that the flow pattern has good agreement with the results of FEM that based on the use of hydraulic presses with initial billet and dies temperatures 410 and 400 ° C, respectively, and different forging speeds 5, 10 and 15 mm/sec. Distribution of effective strain rate, effective strain, effective stress, temperature, forging force and dies­ wear showed improvement the results in forging speed of 5 mm/sec. Processing map of Aluminium alloy 7075 also checked out at constant strain 0.5, indicated that the specified area of the forged part is located in a safe area. Forging force in optimized forging speed 5 mm/sec showed that the forging process using a 1000-ton press can be done easily.

Microsegregation is one of the most important phenomena occurs during solidification. It usually results in formation of some unexpected second phases which generally affect the mechanical properties and specially reduce the workability of casting products. The aim of this research is to study the effect of cooling rate and grain refinement on the microsegregation in Al-4.8 wt.% Cu. For this purpose two series of experiments were designed. In the first set of experiments, the alloy was melted and cooled in three different rates, i.e. 0.04, 0.42, and 1.08 K/s in a DTA furnace. In the second series of experiments, the effect of grain refinement on the microsegregation at a constant cooling rate of 0.19 K/s was investigated. Al-5Ti-1B master alloy was used as grain refiner. Results showed that by increasing the cooling rate the amount of non-equilibrium eutectic phase increases from 5.1 to 7.4 wt.%, and the minimum concentration of solute element in primary phase decreases from 1.51 to 1.05 wt.% Cu. By grain refinement of the alloy, the amount of non-equilibrium eutectic phase decreases from 5.5 to 4.7 wt.%, and the minimum concentration of solute element in the primary phase increases from 0.98 to 1.07 wt.% Cu. So it is concluded that increasing cooling rate in the range of 0.04 to 1.08 K/s, increases and grain refinement reduces the microsegregation.

Equal-channel angular pressing (ECAP) combined with the Conform process provides a solution for the continuous production of ultrafine-grained materials. In the present study finite element method was executed to investigate the effects of die channel angle and friction on the strain homogeneity and the required torque in ECAP-Conform process. Deformation behaviour of Al 6061 wires was analyzed by using the ABAQUS/Explicit software. Finite element analyses by considering different channel angles (90ᵒ, 100ᵒ and 110ᵒ) and various friction conditions of 0.2, 0.3 and 0.4 were surveyed. The results revealed two distinct trends in which by increasing the channel angle among 90ᵒ to 110ᵒ, the amount of induced plastic strain through the wire reduced about 40%. Also required processing torque was decreased about50%. In addition more homogeneity was observed in higher angle values. The results regarding to equivalent strain, obtained from FE analyses, showed a good agreement with previous studies. Eventually plastic strains and required torque were increased about 8% and 12% when friction coefficient raised between (0.2-0.4).

A modified strain-induced melt activation (SIMA) process was applied and its effect on the structural characteristics and hardness of the aluminum alloy Al–12Zn–3Mg–2.5Cu was investigated. Specimens subjected to a deformation of 40% at 300 °C were heat treated at various times (10-40 min) and temperatures (550-600 °C). Microstructural studies were carried out using optical and scanning electron microscopies (SEM). Results showed that the best microstructure was obtained at the temperature and time of 575 °C and 20 min, respectively. The hardness test results revealed superior hardness in comparison with the samples prepared without the application of the modified SIMA process.T6 heat treatment including quenching to 25 °C and aging at 120 °C for 24 h was employed to reach to the maximum strength. After the T6 heat treatment, the average tensile strength increased from 231 MPa to 487 and 215 MPa to 462 for samples before and after strain-induced melt activation process, respectively. Ultimate strength of globular microstructure specimens after SIMA process has a lower value than as-cast specimens without SIMA process.

B4C–Al2O3 composite powder was produced by aluminothermic reduction in Al/B2O3/C system. In this research, microwave heating technique was used to synthesize desired composite. The ball milling of powder mixtures was performed in order to study the effect of mechanical activation on the synthesis process. The synthesis mechanism in this system was investigated by examining the corresponding binary sub-reactions. The self-sustaining reduction of boron oxide by Al was recognized to be the triggering step in overall reaction.