فصلنامه علوم و مهندسی سطح ایران
پیاپی 8 (زمستان 1388)

This paper considers the effects of plasma nitriding parameters including screen hole size, top lid type (screen or iron plate), temperature and composition of the treatment gas, on the surface properties of DIN 1.6580 low-alloy steel. Nitriding was carried out at 520, 550 and 580°C for 5 hr in the gas mixture of (N2/H2); 3:1 and 1:3. The properties of nitrided specimens were assessed using metallographic techniques, XRD, Micro-hardness measurements, and SEM. X-ray diffraction analysis confirmed the formation of and during the nitriding process. The findings show that the thickness of the compound layer increases with the increase in the treatment temperature and nitrogen percentage in the gas mixture moreover increase in the screen hole size has no effect on the compound layer thickness in the screen top lid condition but that an increase in the screen hole size at the same temperature results in an increase in the thickness of the compound layer in the iron plate top lid condition. The results of micro-hardness measurements indicate that surface hardness increases with the increase in the temperature and nitrogen volume in the treatment gas. It was also found that hardness values obtained using screen top lid are relatively greater than those obtained using iron plate top lid.

In this research nitrogen concentration depth profile in the nitriding process of pure iron has been analytically modelled. The compound region was considered as two separated layers including epsilon (ε) and gamma prime (γ') nitrides over an alpha (α) diffusion zone. The analytical model was constructed based on the binary Fe-N phase diagram system below 590oC and up to 11 wt% nitrogen. Considering relevant initial and boundary conditions, the Fick's second diffusion law was applied for three separated ε, γ' and α zones in a semi-infinite domain. Nitrogen depth profile equations were obtained related to nitriding temperature, time and diffusion distance from the surface. The modelling results were compared with the experimental data from literature and a good agreement was confirmed. Application of the present models indicated that increasing nitriding temperature from 500 to 580oC leads to increasing the maximum nitrogen concentration at the γ'/α interface, higher nitrogen distribution in α diffusion zone and deeper nitrogen diffusion in the substrate. At a certain nitriding temperature, increasing nitriding time up to 10h has a significant effect on the nitrogen distribution, but longer periods have no considerable influence.

In this work the shape and arrangement of dynodes were studied in an electron multiplier tube using the focusing role of electrostatic fields. Since the kind and particularly the work function of the emitting surface of dynode is effective in the number of out coming electrons, therefore dynodes made from curved pieces of hard aluminum were coated with a thin layer of MgO for its low work function in pressure of 10-6 torr. As it will be explained later vacuum coating was performed in several methods. In the absence of applied voltage the ratio of out coming electron current to incident electron current of each dynode was obtained, then one minus each ratio number was plotted against the extractor voltage. Using this diagram the absorption coefficient was found to be equal to 0.134. The ratio of out coming electron current to incident electron current of each dynode was plotted, from these diagrams the multiplication factor of dynodes coated with MgO was found to be equal to 3.7

The sample used in the photo/dark measurement was fabricated in the sandwich Al/Polyamide/TiOPc/Oxadiazole/ITO/Glass. Nanostructure Titanium Oxide Phthalocyanine with the average particle size about 25 nm (TiOPc) is used as Charge Generation Material (CGM). Photoreceptor absorption spectra shows that there are some peaks at wavelengths 282,402,578 and 762 nm and there is no absorption in the region of 402-578 nm. Photo/dark induced discharge curve shows 67% contrast is achieved at 345 ms.

Field effect transistor is of importance in the integrated circuit. The metal electrode is on a silicon dioxide layer and is grown on a silicon substrate. We used silver as the electrode. The structural properties of a single silver layer on top of the silicon oxide film has been studied using synchrotron radiation, sensitive to changes in a chemical environment, permits high resolution photoelectron spectroscopy of nano thickness silver film on top of oxide. The local variations of the demonstrated a good uniformity of coverage oxide film and the weaker electrical field across the thinner oxide film (< 2 nm) respect to thicker oxide film.

In this paper microstructure, phase formation and Vickers hardness profile of the hardfaced layer, Co-based alloys (Stellite-6) filler metal on 410 martensitic stainless steel specimens with 309austenitic stainless steel interlayer were investigated. Gas Tungsten Arc Welding (GTAW) cladding was carried out for deposition. The specimens were investigated by an X-ray diffractometer, energy dispersion spectroscopy (EDS), scanning electron microscopy (SEM) and hardness test. According to the analyzed results, the microstructure of the clad layer consists of eutectic structure, and undissolved carbides dispersed in the matrix of the Co-based alloy with dendritic structure.The dendrites have epitaxial growth. Diffusion of carbon from the liquid Stellite to the austenitic stainless steel took place along grain boundaries resulting in the formation of chromium carbide “arms” that penetrated along the austenite grain boundaries in the interfacial region. The dilution of the clad layer by Fe from the substrate decreases hardness, wear and corrosion resistance. The interlayer resulted in a decrease in the dilution of Fe and increase in hardness

In this paper we improve the limited diffusion aggregation model to study and simulate effects of doping type and current density on the structure of porous silicon.For doping type effects, sticking coefficient and for current density effect, a mean field parameter was applied to the limited diffusion aggregation model. The results of our simulasion show that sticking coefficient influences pore thickness, while mean field parameter controls the tree or rod characteristic, of pores. These theoretical findings are in agreement with experimental abservations.

In this paper, a mathematical relation is presented to determine fracture toughness of Ni-P coatings related to its thickness on the basis of experimental data. For this purpose, Ni-P coatings with various thickness were deposited on the steel substrate and then heat treated for 1 hr in 400 oC. Fracture toughness of the coatings was estimated 1-3 MPa√m by Vickers indentation method. It was found that thick coatings have lower Kc compared to thin ones. Fracture toughness relations (models) were analysed as different functions. Mean square relative error (MSRE) was calculated for final (models). The results showed less MSRE as well as good agreement between model I (Kc=f(t,t2)) and the experimental data

In this resead solar mirrors were made from silver nano layers on a white glass substrate. In this regard the DC magnetron sputtering was used for diposition of silver. ITO layers were used to enhance the adhesion of the main layer. The layers were characterized by spectrophotometery, RBS and XRD. It was observed that IR reflection was enhanced with the increase in Ag thickness. However increase in ITO layer and substrate temperature, and decrease in grain size, decreased the IR reflection.