نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 17 (تابستان 1390)

Nowadays carbon thin films have been used in many application such as wear, electronic devices, biomaterials, and fuel cells.In this study, the properties of magnetron sputtered amorphous carbon films on 316L stainless steel have been investigated as a function of deposition time. The results show that structure of carbon films transforms from amorphous to nano-crystalline. Byincreasing the deposition time, the graphitic clusters increase and then decrease in the long deposition times because of rearrangement phenomenon. According to SZM model and AFM micrographs, the structure of carbon films is located in columnarzone I. Also with increase of deposition time, the electrical resistance of carbon thin films is raised due to intrinsic compressive stress that likely reduces charge careers mobility. The effects of deposition time on the corrosion resistance of carbon films is negligible.

Recently, studies on the bonding strength improvement in NiTi / polymer matrix interface have been aggrandized due to increase of using the intelligent composites in industrial and biomedical appliances. Chemical treatment of the surface is one of the suggested methods that was studied about NiTi / Silicone composite in this research. Pull-out test results showed using acidic and alkaline solutions such as H2O2 and NaOH increases the bonding between the metal strips and the polymeric matrix. SEM micrographs and EDS analysis showed that Sodium titanate performed on the metal surface increases the bonding strength to 11%. Performing oxide layer on the alloy had the same effect and increased the amount of adhesion strength from 332.90 to 625.58 kPa.Increasing surface roughness and friction that was occurred after chemical treatment, can be used in manufacturing of artificial muscles.

Copper base composite reinforced with Cr2O3, because of good electrical and thermal conductivity and strength in high temperature is suitable for contact materials. In this paper composites were made by mechanical alloying and internal oxidation. Inorder to estimate suitable time and ball to powder ratio of milling for mechanical alloying and to ensure of comlete internal oxidation of Cr after sintering, SEM micrograph and XRD analyses were carried out. Properties such as density, specific electrical resistivity and hardness of nanocomposite specimens were improved in compare with Cu(Cr) solid solution. Dry sliding wear test were carried out by using Pin on Disk equipment. As the sliding distance increased, volume loss of composites increased. Wear mechanism of composites were investigated by using SEM micrograph of worn surfaces of specimens. As the sliding distance increased, the dominante mechanism is abrasive, delamination and oxidation respectively.

In this research, a three-step process including spex ball milling, hydrogen reduction, and sintering was used to synthesize W- 15 wt%Cu nanocomposite. WO3 and CuO powders were ball-milled under air/stearic acid for 1, 2 and 3 hours. Then hydrogenreductionwas carried out at 650, 700 and 750°C for 15-90 min and sintering was performed at 1100, 1150, 1200 and 1250°C for 60 min. Morphology and grain size of the products were rigorously investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and nano-particle Zeta-sizer. Results obtained showed that, the mean particle size of the homogenous powders milled under stearic acid for 3 hour was about 63 nm. Hydrogen reduction at 700°C for 90 min resulted an average particles and clusters size of 72.9 and 445 nm, respectively. The results demonstrate that when sintering is carried out at 1200°C for 60 min, the tungsten-copper nanocomposite can be achived with a homogeneous structure and density of about 16.1 ± 0.1 g/cm3.

This paper discusses the application of black chromium coating on steel substrates applicable in solar power plants obtained from the optimum electroplating black chromium bath. Black chromium is one type of selective coatings that used usually in solarpower plants. As absorption and thermal radiation are related to black surface and undercoats respectively, the thickness of absorption layers should be lower than infrared wavelength so that undercoat shows its appropriate optical properties and decreasethe thermal radiation. Since copper have lowest thermal radiation which is due to their high conductivity and also their smooth and polished surfaces, in this research copper selected as an undercoat. The result proves that Electrodeposition of copper on steelsubstrates from sulfate baths is possible. Electrodeposition was carried out at room temperature. The plating time and concentration was variable to find the best coat at minimum amount of copper sulfate. Then Electrodeposition of black chromium was also carried out at different time, temperature and composition of black chromium bath. Adjusting the pH level was not a matter of importance after bath preparations. Adhesion and Uniformity of the coatings were investigated by Scaning Electron Microscopy (SEM).

In this study the effect of in situ Si3N4 formation on the microstructure changes of a cordierite body with nitride bonded was examined. Nano silicon powder was prepared by mechanical process in a high energy planetary ball mill in an Ar atmosphere.Different mixtures of the cordierite with nano silicon particles were prepared and sintered in a tube furnace at different temperatures in a nitrogen atmosphere in order to formation of nitride bonded cordierite composite. Result showed that by using nano siliconpowder formation of silicon nitride increased. It could be related to formation of Si3N4 before formation liquid phase of cordierite during sintering. On the other hand using nano silicon powder it should be possible to produce a high porous cordierite-Si3N4composite with a good thermal shock resistance.

To use steels require the correct selection heat treatment parameters in industreial applications. In martensitic stainless steels, carbides dissolution process in continuous heating and their precipitation in continuous cooling play a main role in their properties.In this study, at different temperatures and cooling rates, the thermal cycles were used on the AISI420 steel by dilatometery technique. The dilatometery results with microscopic investigations showed that the lower austenite grains size and muchconcentration alloying elements in austenite before and after dissolution of carbides, respectively, are parameters that caused alterations of martensite start temperatures (MS) in different austenitization temperature. Beside, precipitation of carbides decreaseswith increasing austenitization temperature and cooling rates under continuous cooling.

The effect of cold-rolling and subsequent heat-treatment on the microstructure and mechanical properties of Fe-Ni-Mn-Mo-Ti maraging steels containing 6% chromium were investigated. Optical and scanning electron microscopy, X-ray diffraction, tensileand hardness tests were used to study the microstructure, aging behavior and mechanical properties of the annealed steels. Cold rolling and annealing of homogenized Fe-Ni-Mn-Mo-Ti-Cr maraging steels resulted in the formation submicrocrystalline Fe2(Mo,Ti) Laves phase particles. A higher volume fraction of retained austenite was found after solution-annealling which transformed to martensite during tensile deformation, giving rise to uniform tensile ductility. This alloy shows moderate tensilestrength (900Mpa) along with high uniform 30% tensile elongation.