نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 45 (تابستان 1397)

In this study, the mechanical properties of dissimilar welding of austenitic stainless steel AISI 347 to low alloy steel ASTM A335 prepared by gas tungsten arc welding process using direct current electrode negative polarity have been investigated. For this purpose, two filler metals including ER309L and ERNiCr-3 were used. In order to achieve suitable structure and excellent mechanical properties in the mentioned joints, controlling of the heat input and preheating were among the effective and controllable parameters. The microstructure of the base metals and weld metals, were evaluated using optical microscopy and scanning electron microscopy was used to analyze fracture surface. Microstructural evaluations showed that a two-phase structure consisting of dendritic and inter-dendritic regions with primary austenite solidification in ERNiCr-3 weld metal, and the primary skeleton-shaped ferrite with austenitic matrix in the 309L weld metal was observed. Also mechanical properties including the bend test, ultimate strength, impact resistance and hardness were investigated. All the specimen underwent ductile fracture in HAZ in the tension test. The maximum fracture energy related to the ERNiCr-3 the welded specimen. The maximum and minimum hardness corresponded to the ERNICr-3 and ER309L, respectively. Finally, it can be calculated that for the joints, between the austenitic stainless steel AISI 347 to low alloy steel A335, the ERNICr-3 filler provided the optimum qualities.

In this study, silica obtained from the rice hush was used to synthesis of Al2O3/SiC nanoparticles. The rice husk is an agricultural residue abundantly available in rice producing countries such as Iran. For this reason, the ash obtained from the burning of the rice hush which contains more than 93% silica, and aluminum and carbon powders with the molar ratios of 3:4:6 were mixed and then pressed into pellets by using a cylindrical die under a pressure 50MPa. In order to conduct the Self-Propagation High-Temperature Synthesis (SHS), the produced pellets were placed in an electrical furnace at 850oC under the argon gas atmosphere. Then, a planetary ball-milling for 4, 8, 12, 16 and 24h was used to decrease the particle size of the synthesized composite. The results of XRF, XRD, SEM and DLS investigations shown that the rice hush ash can be used to fabricate Al2O3/SiC nanoparticles via SHS and ball-milling and the size of synthesized particles after ball milling for 4-24h is in the range of 870-65nm.

This present research was related to electrical conductivity of RGO-ZnO-TiO2 nanocomposite in comparison RGO-ZnO nanocomposite . In order to carry out this research, at first graphene oxide was synthesized by using modified Hummer method and reduction of graphene oxide (reduced graphene oxide(RGO), was done by UV light and temperature. TiO2 and ZnO nanoparticles were synthesized by sol-gel method.XRD,FTIR and DRSUV were used to investigate these nanoparticles.
For sample preparation ,dip coating method was used and all particles were coated on the surface of FTO respectively. for investigation of adding TiO2 nanoparticles on the electrical conductivity and amount of band gap of RGO-ZnO nanocomposite, electrochemical impedance spectroscopy and talc plot were used .
The results of comparison between these 2 samples showed that adding TiO2 nanoparticle to RGO-ZnO nanocomposite reduced band gap from 3.22 to 3.11 and increase resistance from 2.8*104Ω to 5.76*104Ω . with study of level energy of RGO, ZnO and TiO2 nanoparticles ,the reason of increasing resistance related to higher ZnO energy level in comparison to TiO2 energy level and electron Inability to overcome of this level energy in the absence of UV light .with putting this sample under UV light could be reduced this resistance.

In this research, closed-cell aluminum foams reinforced by SiC particles were fabricated using direct melt-foaming method and CaCO3 as a blowing agent. The effect of adding reinforcement particles on mechanical properties of foams was investigated by adding different volume percentages of SiC particles (3%, 6%, and 10%). To obtain the mechanical properties of produced foams, uniaxial compression test was carried on samples at different temperature (100°C, 200°C, 300°C, and 400°C) and constant strain rate equal to 0.1s-1. The compression tests result show that at the constant temperature, the yield stress, Plateau stress and energy absorption stresses of composite foams will increase by increasing the volume percentage of SiC particles and decrease with increase in temperature. Reinforcement particles also increase the number of indentation in the stress-strain curve of foams, which reflects increasing brittleness of the foams’ cell wall.

The aim of this research is fabrication of NbAl3-based nanocomposite via mechanical alloying in order to increase its toughness and high-temperature strength. For this purpose, mixtures of 49 wt.% of aluminum and 51 wt.% of niobium oxides were mixed and mechanically alloyed. Phase evolutions, microstructure and morphology of powder particles during milling were studied using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In order to study the thermal behavior of powder particles, annealing treatment and differential thermal analysis (DTA) were carried out. It was found that the reaction between aluminum and niobium oxide is explosive and during this reaction NbAl3-based nanocomposite reinforced by Al2O3 particle is formed. The as-blended powders were studied by DTA and the results showed that in this condition NbAl3/Al2O3 composite is formed within two stages. At the first step, Nb2O5 is reduced by aluminum. At the second step, the retained aluminum is reacted by niobium and finally NbAl3/Al2O3 composite is formed. Observations by TEM revealed formation of nanostructure and nano-sized reinforcement particles.

In this study, metallurgical properties lap joint of pure copper and 6065 aluminum alloy with friction stir welding technique were investigated. To purpose the metallurgical properties of joint optical microscopy, X-ray diffraction analysis (XRD), energy dispersive X-ray (EDS) and Vickers hardness junction of micro gauge were used. The results shows that due to the direct contact between aluminum alloy and tool shoulder, the microstructure change of AA6065 was more than copper. With increasing tool rotation speed the microstructure size of AA6065 and copper became smaller and with increasing linear speed and cooling rate, the microstructure size of base material became more. The results shows that the structured layers were formed in stir zone which with increasing heat generation they geometry became thinner and stretcher. The combination of base materials in high tool rotation and low travelling speed caused the CuAl2 and Cu9Al4 intermetallic compounds were formed in base metal interface. For changes in microstructure size and formation of intermetallic compounds, the hardness of stir zone was more than other area of joint. The maximum hardness of joint area was 111 Vickers which allocated to the joint that welded with 1130 rpm and 24mm/min tool speed.

Fast pin connecting to the steel parts to fasten cables and wires to the pipelines, anchors inside the cements to the steels structures and bolts inside the tanks is possible just using stud welding method. In this method an electric arc is established between pin and base metal, and partially melt their surfaces, then by applying a pressure, pin and base metal will be jointed. Some parameters such as surface roughness, time of electric arc, the thickness of base metal and current, affect the quality of stud welding. In this research, steel pins are connected to a steel base metal at three different surface roughness and three different current using stud welding method. Results of scanning electron microscopy (SEM) indicates that when the surface of base metal is rough, the interface of joint increases from 50 to 95 percent by increasing the current from 160 to 200 ampere. But that when the surface of base metal is smooth, the interface of joint between pin and base metal decreases from 95 to 50 percent by increasing the current from 160 to 200 ampere. Also the interface of pin and base metal solidify in martensitic form, and the results of microhardness measurement confirms the higher harness of the interface regarding base metal and pin. According to the results of tension test, the maximum strength (400 MPa) was related to the P60-200A sample.

Recycling of industrial scrap of IN317LC superalloys via ESR process is investigated in this article. The purpose of this study is reach to the best chemical composition, microstructure and mechanical properties according to AMS5377E standard. Different levels of TiO2 (0, 3, 6 wt %) were added to 70CaF2-30Al2O3 ESR slag. The results show that in slag wih 3 wt % TiO2, Ti loss compensate by Oxidation-Reduction reaction between slag and melt. As a result of the variation of slag activity, oxygen and nitrogen of the recycled ingot reach to 14.3 and 16 ppm, respectively. In addition, this ingot has the maximum level of γ' particle with minimum size because of high level of (Ti) of this recycled alloy, the good microstructure and the stress rupture life of 47 hr obtained. In the recycled ingot by 6 wt % TiO2, despite of compensation of Ti loss and increase of Ti level, the mechanical properties reduced as a result of reduction of γ' volume fraction.

The inhibiting action of Schiff base and polyethylene glycol (Salpn-PEG) complexes on low-carbon steel corrosion in 0.5 M sulfuric acid was examined using weight loss, potentiodynamic polarization and spectroscopy electrochemical impedance (EIS) techniques. Schiff base N, N’-bis(salicyladehyde)-1,3-diaminopropane (Salpn) was synthesized by salicylaldehyde and 1,3- diaminopropane. PEG/Salpn complex with weight ratio 1:4, 2:4 and 3:4 of Salpn and PEG were prepared in methylene chloride solvent by a simple deporotonation procedure. Obtained Results show that PEG/IMZ complex is very effective corrosion inhibitor of carbon steel in the acid environment in compare with PEG, Salpn and noncomplex form of them. Maximum corrosion inhibition was obtained for PEG/Salpn complex with weight ratio 1:4 of Salpn and PEG. The inhibition efficiency increased with the increase in the temperature up to 45°C and decrease in higher temperatures. Results from all the corrosion tests were examined using SEM and are in reasonable good agreement. Adsorption thermodynamic data (〖K 〗_ads and 〖∆G〗_ads ) was calculated using the weight loss data

In this research, the effect of substrate on the formation of chromium- and vanadium carbide coating was studied by thermal reactive diffusion. The substrate of H13 steel was coated in two kinds of metal and oxide bath with molar ratio of Cr/V=3 for 14 hour at 1000˚C. Carbide coatings including chromium carbide (Cr3C2, Cr7C3), vanadium carbide (V8C7) and the complex carbide phase of Cr2VC2 were formed on H13 steel. The thickness of the carbide coating was 8.5±0.5 µm and 6.5±0.5 µm, respectively in metal bath and oxide bath. The amount of vanadium- to chromium- rich regions in the carbide coating was less than the ratio of vanadium to chromium content in the metal bath. The results of coating in the present study was compared to the results of coating in a similar condition on Ck45 steel. The type of substrate had an important role on the coating thickness and the phase distribution of vanadium- and chromium- rich regions. However, the element distribution in the coating was not affected by the kind of substrate.

A surfactant assisted Co-Precipitation method was employed for the synthesis of magnesium aluminate spinel with nanocrystalline size and high specific surface area. Calcination operations were performed in 800-1000° C for two hours. Different percentages of samarium were doped to magnesium aluminate spinel to examine the properties of magnesium aluminate spinel. The prepared samples were characterized by thermal gravimetric and differential thermal gravimetric analyses (TG/DTA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM), and photoluminescence spectrum (PL). XRD results showed that nanocrystals of magnesium aluminate spinel were influenced by the type of surfactant in 800° C. The results of luminescence spectrum show that by increasing the amount of samarium after 0.15 of weight percentage, concentration suppression happens and reduces the intensity of luminescence properties.

In this study, tantalum (Ta) thin film was deposited on Si(100) and 316L stainless steel (SS) substrates by DC magnetron sputtering. The structural properties of Ta film were investigated by X-ray diffraction analysis. In addition, the scanning and transmission electron microscopies as well as atomic force microscopy were used to study the cross-section and the morphology of the coating. The corrosion behavior of the bare and Ta-coated 316L SS was evaluated by potentiodynamic polarization test. The electrochemical impedance spectroscopy was employed to study the corrosion mechanisms. The results revealed that the structure of Ta coating on either Si and SS substrates is a mixture of αβ phases, while pre-deposition of a thin tantalum nitride seed layer causes to the deposition of pure α-Ta and decrease the sheet resistance from 90 µΩ.cm to 15 µΩ.cm. Microscopic evaluations shows that the Ta coating is compact, homogeneous and defect-free, exhibiting a columnar structure with a surface roughness of less than 6 nm. Furthermore, the corrosion studies show that the Ta coating perform as a physical barrier between corrosive electrolyte and substrate and, in this way, provide a protective efficiency of more than 70%. In this regard, the diffusion of corrosive electrolyte toward the substrates through open porosities was found to be the corrosion mechanism of the Ta coating and the porosity index of the coating was calculated to be about 6%.