فهرست مطالب hamzeh forati rad

The study aimed to investigate the effect of different atmospheres and compositions of aluminum alloys in the fabrication of Al-B4C composites by melting infiltration into porous boron carbide preforms. At first, powder of B4C with 20 μm together with polymeric material was fabricated in porous preform by gel casting method. Then the preform was pyrolyzed at 900°C for 3 hours in a nitrogen atmosphere oven. Next, three different compounds, including pure Al, Al6061, and Al-13.8% Mg2Si, were infiltrated into the preform inside the furnace under an oxidizing atmosphere, vacuum, and neutral gas. To characterize the samples, XRD, SEM, and EDAX analyses and the percentage of porosity of the samples were performed by the Archimedes method. The results showed that the presence of a magnesium atmosphere inside the furnace makes the infiltration process possible due to increasing the wetting agent of metal with ceramic and breaking the alumina oxide shell. Al-13.8% Mg2Si eutectic alloy showed the ability to penetrate the porous body and make a highly dense body. Simultaneous use of magnesium atmosphere and high infiltration temperature prevented the formation of carbide phases.

Ti3SiC2 bulks have been synthesized by infiltrating Si liquid into porous precursor pellets composed of 3TiC/0.3Si. In the first step, in order to find an optimum milling time, the powders were milled at 15, 30, 45, 60, 90 and 120 minutes, then the mixture was cold pressed under the pressure of 80MPa and then infiltrated with molten Si. Based on the results of XRD and Ritvild tests, 60 minutes were selected as optimal milling time. In the second step, in order to determine the best press pressure, the powders were first milled for 60 minutes and then cold pressed under the pressure of 40, 80, 120 and 160MPa and then infiltrated with molten Si. Based on the results of XRD and Ritvild tests, 40MPa was selected as the optimum press pressure. All specimens were infiltrated in a vacuum of 10-4 torr at 1500°C for 1 hour.

Anodizing، as an electrochemical process، has been used for enhancing the corrosion resistance of aluminum and its alloys. The type of current (direct and pulse) strongly affects the properties of anodic films، which are obtained by the anodizing process. In this research، The 1070 aluminum alloy is anodized either by direct current (DC) or by pulse current (PC) (with different frequencies and duty cycles)، in 10%wt acid sulfuric at 10oC temperature. Scanning electron microscopy (SEM) and Potentiodynamic Polarization method (in 0. 5 M NaCl solution)، respectively، are used for characterization of the surface morphology and corrosion resistant of samples، respectively. The results indicate that the pulse current improves the morphology of the anodized samples، but the corrosion resistance of these samples is lower than the sample anodized by direct current. The results also showed that in PC anodizing، Ecorr and icorr of samples are strongly affected by duty cycle. Among the PC samples، the sample is anodized at 200 Hz and duty cycle 70% showed the best corrosion resistance.

Plasma nitriding is one of the effective methods for the improvement of hardness, wear and corrosion resistance of iron alloys. In this research, AISI H11 steel was plasma nitrided with various gas mixtures, times and temperature The effect of process parameters on the morphology and hardness of nitride layers has been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and microhardness measurements. The results showed that by increasing the nitriding time, the depth of nitrogen diffusion into the sample and consequently, the size of nitride precipitates formed on the surface increased. therefore, the density of these particles and hence, the surface hardness decreased. By increasing the nitrogen percentage in the gas composition, the surface hardness increased due to the formation of more ε phase at the surface. Meanwhile, an increase in process time and/or temperature resulted in a decrease in the amount of ε phase which decreased the surface hardness.