مجله مواد نوین
سال ششم شماره 4 (پیاپی 24، تابستان 1395)

In this study, the effects of adding copper sulfate on the properties and corrosion resistance of electroless coating of nickel - phosphorus on aluminum substrates has been investigated. Samples after surface preparation were coated with adding different concentrations of copper sulfate (0.2 to 1 gram per liter) in nickel-phosphorus electroless baths. To examine the coating structure changes with different concentrations of copper sulfate, X-ray diffraction(XRD) was used. In order to evaluate the morphology of the surface , the optical microscope was used and to study the chemical composition and cross-section, the scanning electron microscope equipped with EDS analyzer was used. Vickers hardness was measured using the micro-scale. The corrosion resistance studies were carried out using Tafel polarization test in a solution of % 3/5 NaCl. Test results showed that increasing the amount of copper sulfate in electroless nickel-phosphorus plating bath increases the bath stability and reduce the deposition rate, morphology changes and crystallization of coverage and significant reduction in hardnes were resulted.also corrosion resistance of Electroless nickel-phosphorus coating significantly increased In the presence of copper , due to Reduce porosity and the passire state which was resulted.

Wear is a major cause of damage occurring in workpieces and industrial machins, especially in construction and mining industry. One of the most common and widely used alloys in the above-mentioned industries is Ni-hard 4 cast iron. In the present study, the addition of tungsten to Ni-hard 4 cast iron and its effect on the morphology, structure and wear resistance have been investigated. For this purpose, samples containing of 0, 0.3, 0.7 and 1.1 wt % tungsten were prepared by casting and then heat treatment was applied. After the heat treatment the effect of tungsten on the structure and wear behavior of different alloys in the as-cast and heat treated samples were examined. The structures of the samples were studied by optical microscope and scanning electron microscope furthermore EDS analysis was used to determine the distribution of chromium and tungsten in the different phases in the microstructure. The results showed that the tungsten was solved in the existing phases present in Ni-hard 4 cast iron and fishbone-type and spongy tungsten carbides were formed due to the long-range segregation of tungsten during solidification and also due to the eutectic reaction. Furthermore by applying heat treatment the tungsten carbides dissolved in the eutectic carbides and in various parts of the matrix had a higher potential for a more homogeneous nucleation of secondary carbides. In addition the distribution of the secondary carbide precipitations becomes finer and more uniform. The area fraction of the carbides increased by 4.23% and the average diameter of the carbides decreased from 47.2 to 20.6 μm. As a result the abrasion properties improves.

In this study, effects of using quenching in aqueous salt solution, on the corrosion behavior of Hadfield Manganese Steel was investigated. For making manganese steel according to ASTM A-128C standard, initially two Y-shaped aluminum models prepared and then castings made through Sodium Silicate/CO2 procedure by closed feeding method. Melting was conducted in non-core induction furnace. After the casting, both samples austenitized in 1100°C for 2 hours and then one block quenched in pure water and the other quenched in the aqueous 3.5% salt solution. To evaluate the corrosion behavior of samples, potentiodynamic polarization and electrochemical impedance spectroscopy methods in the 3.5% NaCl solution were used. The results of both methods indicates corrosion resistance of salt bath quenched sample is significantly higher than the other. This is due to:
a)-salt solution quenching medium decreased the amount of carbides in the microstructure and prevented the formation of galvanic cell.
b)- Quenching in salt solution increased the solubility of carbon in the austenite phase that caused the reducing the amount of grain boundaries.

Different constitutive models are used to model the hot deformation flow curves of different materials. In this research, the hot deformation flow stress of API X65 pipeline steel was modeled using the exponential law equation with strain dependent constants. The results of this model were compared with the results of a model which has recently been developed based on a power function of Zener-Hollomon parameter and a third order polynomial function of strain to power of m (m is a constant)). Root mean square error (RMSE) criterion was used for this purpose. It was found that the he exponential law equation with strain dependent constants has a better performance (lower RMSE) to model the hot deformation flow curves of API X65 pipeline steel. The results can be used further for mathematical simulation of hot deformation processes.

In the past decade, researchers have focused on the nano and micro composites for improving the tribological properties of epoxies. Hence, in the current work, tribological properties of milled E-glass, S-glass, and high strength carbon fiber reinforced epoxy composites have been studied. As received fibers were chopped and milled by an attrition mill, and their morphologies were evaluated by Scanning Electron Microscope (SEM). The epoxy composites were prepared simply by mixing and stirring 1wt.% of the milled fibers with a conventional hot-cure epoxy resin. Pin-on-Disc tests were performed on the composite samples to evaluate their tribological properties, especially their friction coefficients and wear rates. The governing wear mechanisms of the as test samples were determined through the SEM images of the worn tracks. Shore-D hardness test was conducted for comparing the hardness variations. Results show that not only the friction coefficient of the milled S-glass fiber reinforced epoxy composite is decreased magnificently from 0.524 to 0.066 in comparison to pure epoxy, but also it has a higher hardness and its wear rate is the same as the pristine ones. Moreover, the wear rate of the milled carbon fiber reinforced epoxy composite is reduced 13% in comparison to the pristine epoxy. The current study shows that the friction coefficient of the E-glass fiber reinforced epoxy composite is a little lower than that of the pristine one, but both of them have the same wear rate.

The unique properties of boron powders will make an attractive prospect for practical applications in many industrial fields. Therefore, investigation of the effective agents on preparation of this material is very important. In this research, the effect of milling atmosphere on synthesis process of the boron nanopowders and properties of final products was investigated in a planetary ball mill. The process was performed using stoichiometric amounts of B2O3 and Mg powders as reactants (7.3 g). Milling was carried out at room temperature with a ball-to-powder weight ratio (22:1) and with a rotation speed of 520 rpm, in argon and air atmospheres for 9h, separately. Milled powders were leached by hydrochloric acid (25 wt%) and distilled water (twice) and the final products were dried. According to the obtained results, the amount of final product and its purity were more in the argon atmosphere than air. The EDS analyses results showed that boron powder can be prepared with the purity of about 90% in the mentioned conditions in the argon atmosphere. In addition, XRD analysis revealed that the product has a non-crystalline structure. Also, SEM observations confirmed the particle size distribution of between about 48 to 81 nm.

In this paper, sandwich rolling of a thin steel sheet with aluminum layers and its conventional rolling process have been investigated and compared. Stainless steel SUS304 for the sheet and aluminum 1050 for the output layers have been used. Both the rolling procedures have been analyzed by the finite element (FE) method with work harden material behavior and FE model has been verified using the experimental results. Then strain, pressure distribution, required rolling force and moment for the rolling processes have been compared. The affect of the sandwich rolling parameters such as deformation ratio, tension forces, friction factor and roll radius have been investigated. Results show that the FE model is in good agreement with the experimental results. Uniformity of the strain distribution in the steel layer for the sandwich rolling is better and the rolling force is considerably smaller than the conventional rolling process but the rolling moment is larger in the sandwich rolling. In the sandwich rolling, by increasing the deformation ratio, output layers thickness decrease linearly. Applying the tension forces on the sheet causes the rolling force decreases and affect of the back tension is more than the front tension. By increasing the friction coefficient, maximum pressure point (neutral point) transmitted to the entrance of the roll gap and uniformity of the strain distribution decreases. Increasing the radius of the rolls, increases the rolling pressure and transmits the neutral point to the entrance of the roll gap without much change in the thickness of the layers.

Nanocomposite gears based on Polyamide 6/Polypropylene (PA6/PP 67/33) blend containing 2.5 to 10 (wt%) of nano-CaCO3 and 5 (wt%) of maleated polypropylene (PP-g-MAH) as compatibilizer were prepared by injection molding. The wear and temperature of gears were characterized against the time by employing a gear testing rig. The ends of gears working lives at which the permanent deformation was happened and, as a consequence, power transmission interrupted, under output torque 14.8 Nm were obtained. The inclusion of nano-CaCO3 led to the 5 °C reduction of gears working temperatures. The maximum life under the torque of 14.8 Nm, was observed in nanocomposite gears containing 2.5 (wt%) of nano-CaCO3 was nearly 2.5 times higher than that of neat PA6 gears. The raise of gears durability by inclusion of CaCO3 nanoparticles was attributed to the improvements of gear teeth flexural and wear resistances.