نشریه مهندسی متالورژی و مواد
سال بیست و ششم شماره 2 (بهار و تابستان 1394)

In this study، nickel was electrodeposited onto the surface of AZ91 Mg alloy and its corrosion resistance was compared with those of AZ91 Mg alloy and pure nickel using polarization and electrochemical impedance spectroscopy (EIS) experiments in a 3. 5 wt. % NaCl solution. The structure of coating was investigated by means of X-ray diffraction، and the specimen’s morphology and the coating’s chemical composition were analyzed using scanning electron microscope (SEM). The results showed that the coating has a nano-crystalline structure with the average grain size of 95 nm. The results of corrosion tests showed a decrease in the corrosion current density from 2. 5×10-4 A. cm-2 for the uncoated sample to 1. 5×10-5 A. cm-2 for the coated specimen، as well as an increase in the corrosion potential.

According to the recent technological developments in modern industries such as automotive and aerospace industries، the use of materials which can retain their mechanical properties at elevated temperatures is essential. Considerable developments which have been made on intermetallic compounds and their applications show that such industries need to use these materials. Nowadays، Zirconium tri-Aluminide intermetallic has attracted much attention due to its good thermal stability and high specific strength. In this study، Al3Zr compound was produced by mechanical alloying. The results showed that no new phase is produced in the powder mixtures after 50 hours of mechanical alloying. After heat treating the mechanically alloyed powder at 600 ºC for 1 hour، the Al3Zr compound was formed. The grain size of the Al3Zr compound was measured to be 32 nm.

In this study، the thermodynamic factors with effects on the formation of non-equilibrium solutions in mechanical alloying have been investigated. The analyzed factors were the interface energy، the interface curvature and the stored energy of amorphous phase. For this purpose، a geometrical model with statistical considerations was first developed in order to investigate the dual-phase nanostructured systems. The mechanically alloyed Cu-Fe samples with the same weight percents were then prepared. The results of experimental XRD and TEM investigations were combined with those obtained from modeling. A comparative study was conducted for the effects of the mentioned factors. It was shown that the high solubility limit in the Cu-Fe system can be obtained by the continuous formation of amorphous nanometric regions and their subsequent transformation to solid solutions.

Wear and erosion are the main reasons for destruction of many industrial components. In many cases، ceramic coatings produced by plasma spraying technique improve wear and erosion performance of industrial components. In this study، it was attempted to design and prepare an optimized composite coating of Alumina-Titania via plasma spraying technique using various parameters of plasma input power، and to study the influence of morphology، microhardness and elastic properties of prepared coatings on their erosion behaviour. Characterization of prepared coatings was performed using X-ray diffraction (XRD) technique and scanning electron microscope (SEM). The elastic properties of coatings and the porosity and gamma alumina phase in their structure were also investigated. Vickers hardness test was performed in order to measure the microhardness of coatings. The results showed that the elastic properties have the greatest influence on the erosion performance of coatings. It was also shown that the input power of 28 kW causes an increase in both the microhardness and elastic properties of coatings simultaneously.

In this research، the first step of reactions in ilmenite-aluminum-graphite system for the formation of Al2O3-TiC/Fe composites was investigated by the study of the binary system of aluminum and ilmenite. The milled and pressed samples prepared by the synthesized ilmenite and aluminum powders having the molar ratio of 1:2 were heat treated at the critical temperatures obtained from DTA analysis. It was found that a transient Fe phase is formed along with TiO2. The spherical shaped Fe2Ti phase was then formed in the matrix consisting of TiO2 and Al2O3.

Polyamides are engineering plastics that have many applications in different industries. Using mineral fillers، the thermal and mechanical properties of these plastics can be improved. This research has been conducted in order to improve the properties of polyamide. In this paper، Polyamide 6-γ-Al2O3 modified with ethylene octene copolymer and grafted by maleic anhydride was synthesized using a double-screw extruder. The weight percents of alumina powder were considered to be 5، 10 and 15%. The mechanical and thermal properties as well as the morphology of the composite samples were examined. It was observed that the tensile strength and impact resistance of polyamide 6-gamma-alumina are improved using the gamma-alumina and EOC-g-MAH، respectively. The study of morphology of the composite samples with scanning electron microscope (SEM) also showed that there exists a favorable distribution of alumina particles in the polyamide matrix so that this homogeneity was considered to be due to the appropriate mixing stage which was conducted within the double-screw extruder with the application of high shear stresses. Thermal properties of the composite samples were investigated using TGA thermal analysis and the results showed that the resistance and thermal degradation of the samples increase with an increase in the amount of alumina used.

In this research، aluminum foams reinforced by alumina and silicon carbide particles (5، 10 and 15%wt.) containing sodium chloride as the space-holder component were produced by powder metallurgy method. Strength properties of composite foams (yield strength and elastic modulus) were significantly increased compared with aluminum foams. The presence of ceramic particles within the foam cellular structure caused the compressive stress to be transferred into the ceramic particles and led to an improvement of the strength properties. The aluminum foams reinforced with 10%wt. silicon carbide among all the composite foam samples showed the best mechanical properties (i. e. the yield strength of 11. 85 MPa and the elastic modulus of 0. 617GPa).

In the present work، the magnetic properties of Fe-P alloys were investigated. The investigations showed that the magnitude of coercivity decreased by conducting two annealing treatments on samples. Samples having the highest amount of Phosphorous exhibited the lowest resistivity. Microstructural studies revealed that the prepared samples were free from Fe3P precipitate and the average grain size increased with an increase in the Phosphorous content giving rise to the decrease of hysteresis losses. Furthermore، amongst the whole prepared samples، Fe-1. 1at. %P alloy showed the lowest hysteresis loss and eddy current loss as well as the highest magnetic induction.

In this study، a borosiliconized protective coating was deposited on H11 steel using the pack cementation method. The effect of processing parameters on the formation and growth of borosilicon layers was investigated at different conditions، i. e. the temperatures of 1000 °C and 950 °C for 3 and 6 hours، respectively. The layers were characterized by means of optical and scanning electron microscopes and X-ray diffraction in terms of their morphology and different phases formed during the treatment. Two distinct regions were found in the coatings consisting of a compound region and a diffusion layer containing undissolved carbides. The hardness numbers were in the range of 500 to 700 HV. An increase in the process temperature and time showed an effect on the formation of undissolved carbides.

In this study، the wear behavior of UHMWPE based hybrid composites reinforced with short carbon fibers and silica nano-particles at room temperature were investigated. The composite samples were fabricated by melt mixing process using the paraffin oil in order to overcome high viscosity of the polymer matrix. Finally، the wear tests were performed. The results of wear tests showed that the weight loss of the composite decreases noticeably in the presence of carbon fibers. It was also shown that the effect of nano-particles depends on their weight percent. The surfaces of the composite samples after the wear tests were investigated using a scanning electron microscope (SEM).