نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 37 (تابستان 1395)

Metal hollow spheres are successfully used for manufacturing of cells and porosities in the cellular structures and metallic foams that important production methods of them are based on powder metallurgy. In this paper, steel hollow spheres are produced by powder metallurgy method and polystyrene beads are used as substrate materials. Polystyrene beads are separated from a polystyrene block and sorted by sieving. Then, mixture of sodium silicate, as binder, and iron powder was sprayed on prepared beads. After drying, a thin layer of iron powder was covered polystyrene beads. Finally, two different heat treatment processes to produce high strength steel hollow spheres was undertaken. These processes are involving the pyrolysis of polystyrene beads and sintering process. For shell thickness measurements, determination of porosity content and flaws evaluation, shell section of hollow spheres were studied by optical microscopy. Produced hollow steel spheres are nearly uniform thickness in shell. Size of iron powder particles, cupper content and type of coating of iron powder are strongly affected on shell thickness, porosity percent and shell flaws.

Interdigitated array electrods1 were prepared by nanolithography of gold on alumina substrate via PVD method. ZnOnanorods used as sensor were synthesized by hydrothermal method on a spotter-coated seed layer of zinc oxide. The synthesized nanorods were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Sensor functioning was investigated with regard to four alcoholic gases. In order to improve the sensing conditions, the sensitivity and response of ZnOnanorods in the temperature range of 50-300°C were studied. The working temperature of 47°C was selected as the optimal temperature and important variables such as sensitivity of the sensor, response time, and recovery time were obtained for the four testing gases at constant temperature and different concentrations. Results revealed that by usingZnO array nanorods,alcoholic gases with highsensitivity can be detected.

The temperature measurement of steel bar is a significant parameter in the hot-rolled steel processing. Furthermore, measuring of steel bar temperature at real time requires an automatic intelligent electronic system such as machine vision system. In this study, a machine vision system is proposed (designed)to provide appropriate images of the steel bar in furnace, process images based on discrimination thresholds and to extract feature (the temperature measurement of steel bar). The threshold limit value for three different temperature ranges; (1200°C -1500°C), (900°C -1200°C) and (600°C -900°C) are assumed to be 1, 2 and 3, respectively, to investigate and analyze variable lighting conditions in HSI color space using genetic algorithm (GA HSI). The performance analysis of proposed GA HSI reveals that color image segmentation by GA HSI and cluster analysis methodhave the same performance. Therefore, this method can overcome the effect of lighting conditions with acceptance of an error range.

The age-hardening curves of hardness measurements obtained for Ni-Span C 902 superalloy under different amounts of cold work, aging temperatures and times showed leveling and pronounced oscillations, indicating instability and reflecting a competition between the effect of sub-structure coarsening and the effect of solute drag and precipitation hardening. An artificial neural network (ANN) was used to model the nonlinear relationship between the parameters of the aging process and the corresponding hardness measurements. The predicted values of the ANN are in accordance with the experimental data. Results showed that the non-deformed and 50 pct cold rolled alloy exhibited a maximum hardness at a tempering parameter of 22 and 21, respectively.

In this Investigation two type of hard face coated electrodes (Fe-Cr-C) used as a hard facing alloys with different ratio Cr/C. The welding of hard facing electrodes were done in similar heat-input but in different of deposited layers on ST32 mild steel. The OES, OM, SEM and XRD techniques used for determining of chemical analysis and study of microstructure characteristics of hard face samples. In addition the thermal fatigue test were done at 600-25 OC for different samples and hardness test used for determining the hardness of hard face layers. The XRD examination Results indicated that microstructure of hard facing layer sample (AB electrode) includes primary carbides and eutectic (), the microstructure of hardfacing layer sample (SD electrode) includes austenite馪笢. The hardness result indicated that hardfacing samples (AB electrode) have maximum hardness which 52-58HRC and hard facing samples (SD electrode) with austenite martensite microstructure have minimum Hardness (30-50 HRC). The thermal fatigue Test results indicated, the highest fatigue life related to the sample that hard-faced with the SD electrode (Ø=4 mm) at a single layer and the lowest thermal fatigue life related to the sample that hard-faced with AB electrode (Ø=3.25 mm) at two layers. It was also found that there is an inverse relationship between hardness and thermal fatigue life of specimens.

Nano-composite coating of Ni-Co/SiO2 is produced by the direct current electrochemical deposition method on the steel substrate. The analyze of X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) are prepared by a nickel-cobalt alloy coatings and Nano-composite coating of Ni-Co / SiO2 that the electrochemical condition were the same in all of them and their grain size and their surface morphology were compared and analyzed. The grain size of Nano-composite coating was less than the alloy coating and surface morphology of the Nano-composite coating was finer and smoother than the alloy coating. The hardness of Nano-composite coating was more than alloy coating. If the electrolyte temperature be 50 degrees Celsius, then the Nano-composite coating of Ni-Co/SiO2 will have the maximum hardness. Adding surfactant to the electrolyte prevents agglomeration of nanoparticles and thus, increases the amount of particles in the coating and the micro-hardness of the Nano-composite coating of Ni-Co/SiO2.The effect of SDS was more than CTAB for the produced coating and the most optimal value for the SDS concentration in the electrolyte was 0.3 grams per liter.

Pzyrygrm flexible base alloy Fe-36Ni in the cast condition and the presence 05/0 and 04/0 wt% wt% aluminum, titanium in the temperature range ° C1150-850 with strain rate s-101/0 were studied. Microstructural studies showed that the addition of aluminum, aluminum-containing deposits such as aluminum oxide structure significantly increases. This strain has been focusing deposits suitable locations, as well as Qflshdn grain boundaries that are leading to the loss of flexibility. Titanic also formed deposits of titanium dioxide and titanium nitride grain size reduction and enhanced flexibility Pzyrygrm.

The relatively new solid state welding process friction stir welding (FSW) was applied in this research work to join similar and dissimilar aluminum alloys AA5754-H22 and AA6063-T4. Different welding rotational speed and transverse speed applied. The joint which was fabricated using tool rotational speed of 2000 rpm and transverse speed of 4 mm/min yielded the best mechanical properties. Soundness of joint was proved by non-destructive tests such as visual inspection and radiography. The global mechanical behavior of the similar welds is very similar to that of the base material. For dissimilar weld important losses in ductility was reported. Microstructural evaluation of fractured surface showed that ductile fracture was the major fracture mechanism of similar and dissimilar welds.

In this study, to achieve the appropriate composite of natural apatite-diopside with desired bioactivity properties, the various compounds containing 10, 20, 30 and 40 wt.% diopside were prepared and compressed under the two-steps sintering heat treatment. Then the mechanical strength, density and bioactivity of the samples were evaluated. Scanning Electron Microscope (SEM), X-ray energy dispersion spectroscopy (EDS) and X-ray diffraction analysis (XRD) were used in order to sample's characterization. Results showed that the sample with 20 wt.% diopside had the highest strength (63 MPa), and the SEM images and EDS spectrum confirmed that the apatite diposits is formed on the surface of this sample after 28 days immersion in simulated body solution (SBF). Ion measurment showed the decrease in concentration of Ca ions from 100 to 93 ppm and P ions from 31 to 28 ppm which indicates the formation of apatite on the sample. By considering the obtained results, the composite sample containing 20 wt.% diopside and 80 wt.% natural hydroxyapatite as a ceramic nanobiocomposite with desirable mechanical properties along with appropriate bioactivity could be introduced for medical purposes such as orthopedic.

In the current research, the effect of silver (Ag) nanoparticles on the crystallinity of polyethylene was investigated. For this purpose, Ag nanoparticles were synthesized using chemical reduction method and characterized by X-ray diffraction (XRD), UV–visible spectroscopy, and transmission electron microscopy (TEM). The mean particle size of Ag NPs was determined about 21.7 nm. The polyethylene-silver Nano composites (PESNs) containing different Ag contents (5, 10, 20 and 30 wt%) were fabricated by mechanical milling method. After the characterization of samples by XRD and scanning electron microscopy (SEM), effect of Ag nanoparticles on the crystallinity of polyethylene was investigated by Nara and Komiya method. Results show that the crystallinity of polyethylene increases from 63.64% to 77.67% as Ag NPs content increases from 0 to 30%.

In this research the AA 6061-T6 aluminium alloy plates were welded by friction stir lap welding method. The effect of welding speeds on micro- and macro-structures and mechanical properties was investigated. The welding process was conducted by welding speed in the range 20-60 mm/min at constant rotation speed of 1000 rpm. The results showed that with increasing of welding speed, tensile shear strength and joint efficiency were increased from about 126 to 132 MPa and from about 40.6 to 42.5 (%), respectively. Although average micro-hardness of the weld nugget zone (WNZ) rather than the heat affected zone (HAZ) were increase with increasing welding speed, the average grain size in the WNZ and in the HAZ was decreased from about 43 to 32 µm and from about 99 to 87 µm, respectively. Due to increasing welding speed, the EPT with an increase in welding speed the hooking and thinning defects were gradually restricted from the WNZ to the WNZ/TMAZ interface. The fracture mode within the highest tensile shear strength joints was denoted as plate separation along the hook throughout the stir zone.

In this paper wrought aluminum sheets with thickness of 5 mm were square butt welded by friction stir lap welding (FSLW) and gas tungsten arc lap welding (GTALW) methods to campare their corrosion behavior.
of the welding zone was probed by tafel polarization curve. Optical metallography (OM) and scaninig electron microscop (SEM) were used to study morphology. Energy dispersive spectroscopy (EDS) were used to analysis different zone of the welds. EDS analysis proved deposits of iron and silicon in samples. FSLW and GTALW resulted in equiaxed grains of about 5 and 18 micrometr respectively, while GTALW caused dendritic structure of the welded region. To assessment mechanical properties, micro hardness test were accure. Resistance to corrosion was greater for the FSLW grains than the GTALW structure. In both cases, susceptibility to corrosion attack was greater in the welded region than the base metal section. . microhardness of FSLW specimen were grater than GTALW specimen.

Magnesia–Doloma refractories are considered as a mixed product of alkali products i.e. sintered (fused) magnesia and doloma in which 50-80wt% magnesia is contained. These refractories enjoy some advantages such as high slag resistance corrosion, high-temperature performance, potential for production of pure molten iron and low cost due to abundance of magnesia and doloma resources in access. However, poor resistance of hydration can be cited that may constrain the amount of this refractory in various industrial applications. in this work the effect of nano-sized Fe2O3 on microstructure and hydration resistance of MgO-CaO refractories with 35wt.% CaO were investigated. MgO-CaO refractories with 35wt.% CaO content were prepared by using dolomite and magnesite calcined as starting material and nano-sized Fe2O3 as additive. Samples were uniaxially pressed in to briquettes at a pressure of 90 MPa. Briquettes after drying at 110 for 24 hr were sintered at 1650 for 3 hr. Hydration resistance was measured at 25oC in 95% relative humidity through the weight gain after 72 hr. according to the results, with the addition of nano-sized Fe2O3, bulk density and hydration resistance of the samples increase while apparent porosity decreased. Densification of MgO-CaO refractories was promoted with increase of nano-sized Fe2O3 content. nano- sized Fe2O3 addition lead to formation low melting phases such as C2F(2CaO.Fe2O3), CF(CaO.Fe2O3) and C3A(3CaO.Al2O3). Formation of this low melting point surrounding the CaO and MgO grain and grain boundaries and promoted densification of MgO-CaO refractories. The nature of nano-sized Fe2O3 promoting densification is promoting the liquid phase sintering.

Single layer and functionally graded coatings of hydroxyapatite and TiO2 particles were deposited on Ti-6Al-4V titanium alloy substrate by electrophoretic deposition technique (EPD). The coatings chemical composition and morphology were investigated using energy dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM) and X-ray diffraction (XRD) methods. The results showed in HA/TiO2 functionally graded coating, the composition varied from inner layer to top layer as 100 %wt TiO2 to 100 %wt HA. To investigation biocompatibility of the coatings, the culture Wharton’s Mesenchymal Stem Cells was used. The results showed the HA/TiO2 functionally graded coating and HA single layer coating were more biocompatible in comparison to TiO2 single layer coating. The adhesion strengths of the coatings were measured by shear testing and the results showed that the HA/TiO2 functionally graded coating has more adhesion strength (~31 MPa) compare to HA single layer.

In this study, ordered ZnO/CeO2 nanocomposite arrays were synthesized within the monolithic cordierite honeycomb using a simple, green and cost effective hydrothermal method. Primary ZnO seeds with (0 0 2) texture were grown within honeycomb’s channels by dipping technique and subsequent heating of the substrates at 350˚C. The average diameter of ZnO seed particles was estimated to be 60 nm from SEM micrographs by the use of Digimizer software. Highly aligned, compact and homogenous ZnO nanorod arrays with the diameter of 200 nm were formed in monolithic cordierite honeycomb by a novel two-step hydrothermal method at 80 oC. ZnO nanorod arrays were used as a core for the preparation of ceria coating. A ceria coating was deposited on ZnO nanorods in the second step of hydrothermal synthesis. Formation of ZnO and ceria phases was also confirmed by X-ray diffraction results.

In this study, the pitting corrosion behaviour of Al-Nano ZrO2 Nano composites fabricated by Accumulative Roll bonding (ARB) process was investigated. Strips of 1050-aluminum alloy of length 250 mm, width of 40 mm, and thickness of 1 mm annealed at 623K in ambient atmosphere and analytical grade of ZrO2 powder with an average size of 40nm were used as raw materials. The Al-Nano ZrO2 composite was produced in 5 cycles. For electrochemical measurements, the square specimens of 10mm×10mm×1mm were cut, connected to copper wires and cold mounted. The open circuit potentials (OCP) of the specimens were measured after 24h immersion in the artificial seawater (3.5wt% NaCl), then Cyclic Polarization test were carried out at range of -0.25 / 1 v with respect to OCP and scan rate of 1mV/s. The results of Cyclic Polarization test indicated that when rolling cycles increase, the Eb and Eb-Erp decrease. The repassivation improved by decrease in Eb-Erp. SEM images represent the decrease and uniform distribution of pits on the surface of samples by increasing the rolling cycles.

In this study, the effect of cooling rate and copper addition was taken into consideration in non- equilibrium eutectic transformation of binary Al-Cu melt via cooling curve analysis. For this purpose, melts with different copper weight percent of 2.2, 3.7 and 4.8 were prepared and cooled in controlled rates of 0.04 and 0.42 °C/sec. Results show that, latent heat of alloy highly depends upon the post- solidification cooling rate and composition. As copper content of alloy and cooling rate increase, achieved non- equilibrium eutectic phase increases that leads to release of much latent heat and appearing of second deviation in cooling curve. This deviation can be seen in first time derivative curve in the form of a definite peak.

At present, Continuous casting is the most important method of producing ingot in the world. The controlling parts of melts are shroud, stopper and submerged entry nozzle (SEN), which are special refractories. Among the special refractory components, SEN is very important. The duty of SEN is pouring the liquid steel from tundish to crystallizator. The aim of this study was to investigate the causes of corrosion and failure of the soundless SEN that used in continuous casting of Saba Steel Company. At the beginning, different sections of a sound and soundless SEN were prepared. Bulk density, apparent porosity, XRD, XRF and scanning electron microscopy was performed in this research. The results showed that unsuitable coating applied on the surface of SEN and less graphite content of zirconia graphite body of SEN are the major causes of failure so that the soundless and sound nozzle has 8 and 10 graphite percent, which leading to decreased resistance to thermal shock and corrosion.

Thermal conductivity, specific heat capacity, enthalpy, entropy and free Gibbs energy of Zn55Al and Zn5Al alloys with additive erbium were studied using a new device according to cooling newton's law. It was observed that with increasing temperature, specific heat capacity, enthalpy and entropy of the alloys increase. A sharp reduction in thermal conductivity and specific heat capacity showed that in all the systems, there is the second order phase transformation about temperatures of 520 to 530 K. The thermodynamic factors are calculated.