Journal of Advanced Processes in Materials Engineering
Year:2011 | Volume:5 | Issue:1 (16)|Papers Count:8

Aluminium matrix composites have found wide application in the industries such as aerospace, automobile, electronics and etc, due to their high strength/weight ratio. In Recent years, much research in the field of mechanical alloying process for the synthesis of advanced materials has been done. In this research work, aluminium matrix composite with Al2O3-TiN reinforcement particles was produced using mechanical alloying method. Aluminum and titanium oxide powders were used as raw materials and milling was performed under N2 atmosphere with 5 atmosphere pressure. The results showed that reduction of TiO2 by Al is the first step of synthesis process and the process continous, Ti react were does with Al remaining or N2. When Al/TiO2 Ratio molar is equal to 1.4, the product synthesis after 10 hours, milling were titanium aluminide and Aluminium oxide and will not produce any value of TiN. With reducing value of aluminum and reaching the Al/TiO2 Ratio molar is equal to 1.2 and 1.3, after 10 hours milling, TiN peaks appears in the XRD results.

In this research, the possibility of providing of titanium carbide and its nanocomposite from rutile as an inexpensive material, Al and Si powder using mechanically activated sintering was studied. Primary mixture was milled in a planetary ball mill at 10hr, 20hr and 60hr milling time. When Al as reduction reagent was used results showed that after 10hr milling, the combustion reaction between Al, TiO2 and C was started and promoted by a self-propagation high temperature synthesis. By extension of milling time to 20hr, the reaction was completed. In final stage of milling, Alumina and titanium carbide crystallite sizes were less than 28 nm. For samples 20hr milled, TiC-Al2O3 nanocomposite was heat treated at 800oC and 1200oC for 1hr. No significant phase change was observed after annealing of the synthesized TiC-Al2O3 powder. And grain sizes remained at scale of nanometer. When Si as reduction reagent was used the results showed that after 10hr milling, rutile reduced to intermediate oxides and also, Si peaks was observed on XRD pattern. With increasing milling time from10hr up 60hr, the no effect of titanium carbide was observed and only the peaks width of XRD patterns of Si was increased while their intensity decrease. The activated powders were synthesized at different temperatures in tube furnace under the argon atmosphere. The XRD results showed that with increasing milling time the synthesizing temperature remarkably was decreased.

In this investigation hypereutectic Fe-Cr-C hardfacing alloy with constant ratio of Cr/C=6 fabricated by GTAW on AISI 1010 mild steel substrate. OES, XRF, XRD, OM, SEM, EDS, WDS techniques and microvickers method were used for determining chemical composition, hardness and studying the microstructure characteristics. The metallographic examination results indicated that hardface samples had three metallurgical zones with different thickness, compositions, microstructure and microhardness. The microstructure in essential (thicker) zone consisted of primary (Cr, Fe)7C3 Carbides with g+(Cr, Fe)7C3 eutectic structure. SEM, EDS, WDS examination and microhardness test results indicated that primary (Cr, Fe)7C3 carbides in essential zone, have different size, area density, chemical compositions and microhardness. The size, atomic percent of chromium and microhardness of primary (Cr, Fe)7C3 carbides from substrates to top surface increased and area density of them decreased.  In addition volume fraction of eutectic phase and eutectic carbides distance from substrate to top surface increased. Therefore it can be divided essential zone to three metallurgical areas.

Because of intense segregation during solidification of Inconel 718, direct mechanical working on cast ingots is not possible. Therefore, the purpose of this investigation is to determine proper homogenization and thermo-mechanical cycles that are need to convert cast ingot to wrought condition. To do so, different homogenization and hot forging cycles were carried out on cast ingots to investigate microstructural changes. The resulting microstructural evolution was evaluated by optical and electron microscopes. Finally, a homogenized structure accompanied with a uniform distribution of grain size (ASTM 2-3) was produced.

Combustion synthesis in the mode of explosion synthesis was used to fabricate TiAl-Al2O3 and TiAl-Ti2AlC-Al2O3 composites. Theses composites were successfully synthesized with compressed samples from elemental powder mixtures of TiO2, Al and C. The XRD analysis was conducted for in situ composites characterization. Scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS) was utilized to confirm results. The experimental results showed that thermite reaction of Al with TiO2 causes to in situ TiAl-Al2O3 composite formation. By addition of carbon powder to thermite mixture, ternary carbide Ti2AlC and TiAl-Ti2AlC-Al2O3 composite was formed. With low carbon in thermite mixture, direct formation of Ti2AlC without of intermediate TiC is reasonable. It is suggest that after TiAl formation, Ti2AlC percipitated from molten TiAl in vicinity of carbon particles. SEM micrographs show that carbon addition to thermite mixture changes the microstructure to a laminated form with plate-like grains.

An interfacial polymerization method for nylon 6, 6 was adapted to produce nanostructured composites with nano hydroxyapatite (n-HA) via in situ polymerization. Nylon 6, 6 was synthesized with hexamethylenediamine and adipoyl chloride via interfacial polymerization method in n-HA slurry to increase homogeneity and biocompatibility. Then as synthesis powders with 60% n-HA content was dried in 80º and was characterized by x-ray diffraction analysis (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and FT-IR analysis. The results showed a uniform dispersion in composites, whereas needle-like n-HA crystals dispersed in condense polymer matrix. Infrared spectrum results showed that n-HA and nylon 6, 6 were mainly linked by hydrogen-bonding, which mainly existed between OH of n-HA and amide of nylon 6, 6. The X-ray diffraction results verified the presence of all characteristic peaks n-HA and nylon 6, 6 in composite powder. The evaluation of mechanical properties of the composite powder approved their accordance to natural bone. The samples were immersed in simulated body fluid (SBF) for bioactivity tests in different periods and results were compared with scanning electron microscopy (SEM) in terms of forming apatite layer.

Flattened wires are used in electronic industries, spring, saw blades and piston rings. In this process, deformation is inhomogeneous because of wire initial geometry. It is important to predict the geometry of flattened roll wire during production, Thus in this research brass wires inhomogeneously deformed using flat rolling in various height reductions. Also flat wire rolling simulated using ABAQUS software. Flat rolling process simulation and geometrical experiments data and the results of previous researchers compared and the accuracy of presented relationship and simulation results investigated. Also new experimental relation developed to study the cross section and length of flattened wires. It is found that presented relationships related to the properties of investigated materials. New empirical relation for length prediction has a good accuracy especially in more reductions.

Effect of applied voltage and electrolyte composition on electrochemical machining (ECM) of intermetallic compound Nitinol is studied. Oxide film breakdown of Nitinol is firstly defined with the use of cyclic polarization test. Anodic dissolution of Nitinol alloy (50%Ni-50%Ti) in three different solutions basically consist of NaCl is carried out in a potentiostat machine. Machining voltage varied from 2 volts to about 30V (potentials higher than Etranspassive). Machining rate (produced current density); current vs. time curve characterization and final surface finish was of interest for study. It seems that Multi Attribute Decision Making can be used for selection of suitable electrolyte and voltage of ECM. Comparing parameters, the best electrolyte and applied voltage was of 300 gr/Lit NaCl + 2.4 gr/Lit NaF and 22 to 26 volts. Roughness exsiting over the surface is related to Nitinol microstructure.