Journal of Advanced Processes in Materials Engineering
Year:2012 | Volume:6 | Issue:2 (21)|Papers Count:12

In this paper, zirconia (ZrO2) nanopowders synthesized via a sol-gel process was investigated at different temperatures. The formed zirconia powders were characterized using BET surface area (SBET) analyzer, Fourier transformer infrared (FT-IR) spectroscopy, thermogravimetric/differential thermal analysis (TG/DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The results showed that this route led to the formation of tetragonal zirconia phase (t-ZrO2) with high crystallinity at 800oC, then the formed tetragonal phase was transformed to monoclinic zirconia phase (m-ZrO2) at temperatures ranging from 800 to 1200oC. The SBET analyzer results revealed that BET surface area of the calcined nanopowders decreased with increasing the heat treatment temperature and consequently increased in the average particle size. Microstructural characterization by SEM depicted that the morphology of the synthesized zirconia nanopowders have changed according to the heat treatment history.

Friction stir welding (FSW) is a new solid-state welding process that can be used to weld aluminum alloys such as Al-2024 that are hard to weld by conventional fusion welding. The grain refining in the stir zone occurs during friction stir welding. The mechanism of grain refining in the stir zone is interest for researchers. The effect of rotational speed and feed speed on the grain size in the stir zone of the 2024 aluminum alloy was investigated in this study. Also the mechanism of grain refining in the stir zone identified. It is found that the grain size of the stir zone increases with the increasing of rotational speed and decreasing of feed speed during FSW. Also it was specified that the mechanism of grain refining in the stir zone is continues dynamic recrystallization (CDRX).

Among the Aluminum-Magnesium alloys, 5083 alloy has specific characteristics such as high mechanical features, good weldability, and the most important of all its excellent resistance to corrosion under water. These characteristics caused 5083 alloy to be used widely in the marine industries. One of the welding methods for this alloy, especially suited for thick plates, is GMAW welding method. In welding process of this alloy, in order to eliminate surface moisture and to avoid porosity, lack of fusion and possible distortion, preheat is needed. In this project Al5083-H321 alloy test plates were welded in six different preheat temperatures with GMAW method, using ER5183 filler metal, to investigate the effects of preheat temperature on microstructure. Optical metallugraphy, macrography and scanning electron microscope equipped with EDS, were used to examine the microstructure of this alloy, and also to determinate the effect of changing the preheat temperature on the size of grains, and created precipitations in weld metal and heat affected zone. Finally three kinds of precipitation included precipitations rich in Magnesium (Al-Mg), rich in Iron and Manganese (Al-Fe-Mn) and also precipitations rich in Silicon and Magnesium (Al-Mg-Si) were observed in this alloy. Besides, increasing the preheat temperature caused an increase in the amount of created precipitations and the size of grains and the heat affected zone (HAZ).

This paper presents a comparative study on the atmospheric corrosion of steel, at two sites, in Iran. Corrosion rate values, time of wetness and the level of pollutants, namely of SO2 and chlorides, in both atmospheres, were determined for the first year of exposure in order to establish the aggressiveness of the atmospheres. The results obeyed well with the empirical kinetics equation of the form C=Ktn.

TWIP steels are a family of high Mn austenitic steels posses both high strength and high ductility among aotumotive body steels. In the present paper, the effect of addition of Mo on improving of mechanical properties of a TWIP steel (Fe-33Mn-3Si-2Al) is investigated. To do this, different amount of Mo were added to the chemical composition of steel and the resulted mechanical properties, microstructure and crystallographic phases were examined after casting, hot rolling and annealing. The results showed that addition of Mo enhances the mechanical properties; however, the optimum strength was obtained by addition of 0.3% Mo. This resulted to a 50% increase to ultimate strength and 40% decrease in grain size.

The loss of light intensity due to the size of crystals and variety between refraction index of glassy and crystalline phases has limited the use of transparent glass-ceramics in optical applications. In this investigation, the effect of b-quartz s.s. and b-eucryptite nano-crystals on light scattering loss have been investigated in lithium alumino-silicate glass-ceramics using Mie and Rayliegh scattering theories. The comparison between theoretical and experimental results of scattering illustarates that precipitation of b-quartz s.s. nano-crystals is reduced the scattering loss due to the almost same refraction index with the glassy matrix. The produced glass-ceramics in this investigation transmit more than 90% of incident light photons and accordingly, they are suitable for optical applications.

Hydroxyapatite (HAp) has an important role play in the bone tissue engineering because of ability for bone regeneration. In this paper, first, hydroxyapatite nanocrystal powder has been made of bovine bone by thermal analysis at 900oC and then HAp porous with 40, 50 and 60%wt produced by polyurethane sponge replication method. Then scaffolds have been coated by poly-hydroxybutyrate (P3HB) in 30sec and 1min times. In terms of phased studies, morphology and specifying agent groups, it has been used of characterization devices as XRD, SEM, TEM and FT-IR, respectively. Finaly has been presented a scaffold with 90% of porous level in size numbers of 100 and 400mm. As the porosity and morphology of scaffold have indicated, the most excellent scaffold was of 50% wt of HAp which can be utilized in bone tissue engineering.

In this research, the corrosion of API 5L 42X steel in contact with rock wool thermal insulation at four temperatures 20, 40, 60 and 80oC is investigated. For this purpose, the tafel polarization, cyclic polarization and weight loss examinations were used. Electrochemical and weight loss tests were conducted in insulation’s leachate and in contact with wet insulation, respectively. Furthermore, in order to confirm of corrosion tests results, the corrosion products that obtained from weight loss measurements at 20 and 80oC, were evaluated by X-ray diffraction (XRD) analysis. The results of tafel and weight loss examinations for 20oC showed that rock wool insulation alone had little talent in the corrosion creation on steel samples, which this outcome of the alkaline nature of it’s leachate and low chloride ion concentration in this insulation. In weight loss measurements due to formation of a close system, by the increase of temperature from 20 to 80oC, the corrosion rate continuously was increased, while such behavior because of formation of an open system was not observed for tafel tests in the temperature range of 60 to 80oC. Cyclic polarization tests and microscopic observations of samples surface after weight loss measurements have shown that the increasing of temperature is increased the tendency to localized corrosion.

Important characteristics such as high strength to weight ratio, toughness, ductility, fatigue strength, wear resistance, high heat conductivity, excellent damping capacity and low notch effect sensitivity beside low production costs result in that Austempered Ductile Irons (ADI) to be so significant for designers and metallurgists. Retained austenite, which is enriched with carbon during isothermal austempering transformation, is the main reason of these unique properties. According to the intricate, costly and inaccurate typical method for determining the amount of retained austenite volume fraction, the purpose of this investigation is presenting an artificial neural network based model to estimate this phase by utilizing an extended database of published authoritative data. Therefore, 2141 data (including 10 inputs; %C, %Si, %Mn, %Ni, %Cu, %Mo, austenitizing time, austenitizing temperature, austempering time, austempering temperature and an output; retained austenite content after austempering) were used for generating a Multi Layer Perceptron (MLP) neural network with 3 to 10 cells in a hidden layer. Activation functions in hidden layer are forms of non-linear, continuous and differentiable sigmoid tangent and output functions are linear. Evaluation test results showed that the selected synthesized MLP-ANN can easily and precisely estimate the amount of retained austenite according to chemical composition and heat treatment parameters, with a negligible error.

The SiO2-CaO-MgO-Al2O3 glass-ceramic with TiO2 additive was prepared via sinter-crystallization method. The thermal behavior of the glasses investigated by means of differential thermal analyser. The sinterability evaluated by measurement of linear shrinkage and density. The sintering carried out at different temperatures from 850 to 1150oC. The experimental results showed that sintering is complete at 1150oC. The addition of TiO2 showed a positive effect on the sinterability behaviour of the sintered glass -ceramic. The only observed crystalline phase was diopside that detected by X-ray Diffraction. Due to the different volume variation of diopside during the crystallization, the crystallization induced porosity, was formed in glass- ceramic. The microstructure of the glass-ceramic was examined by scanning electron microscopy (SEM). The formation of porocity was confirmed by micro structural observation.

The aim of this paper is to produce gypsum product with improved properties. At first the building material with the mixture of gypsum and various additives are tested according to the standard conditions (ASTM test 1369). Absorbed water and cold crushing strength ware measured. Regarding the results, the used additive materials were divided into two branches for decreasing the density and increasing the strength. Samples were studied by choosing one of additives mainly and the effect of the ther were divided into two branches for decreasing the density and increasing the strength. additive considered. XRD and SEM studies were performed. Isinglass improved the properties, but decreased the hydration rate, which could be partly improved by sodium chloride. The best composition was 100g gypsum, 15g cement, 5g pulp, 15g isinglass and 20g sodium chloride.

In most cases, the steel blades used for cutting various types of plastics, rubbers, metals and woods, are made of high carbon steels. By performing the surface hardening heat treatment, makes the hardface layer of these blades for cutting applications. The St37 steel used as a substitute and 4 different electrodes types were used and the hard face layers were fabricated by SMAW process.The results of the chemical analysis were done on the weld metal of the electrodes shows that presence of about 0.5% carbon with different amounts of carbide formeres elements had made different hardness and the wear resistance. The Fe-Cr-Mo-V-W hardface alloy with code "WD" had the highest hardness and wear resistance than does the others. The microstructure of "WD" hardface layers obtained martensite, austenite and alloy carbides. In addition the "WD" sample has the higher hardness and wear resistance in comparison with heat treated hardened CK70 steel samples and can replace for cutting blades applications.