JOURNAL OF NEW MATERIALS
Year:2017 | Volume:7 | Issue:4 (28) |Papers Count:13

In this research, effects of heat input on microstructure, mechanical properties and corrosion behavior of 5083-H321 aluminum alloy welded joints using pulsed MIG process are investigated. AA5083 aluminum alloy is extensively used for many applications in the marine industries. Due to the environmental conditions and the presence of sea water in service, the corrosion behavior of this alloy, particularly the weld zone, has been studied by researchers. Due to lower heat input and the smaller heat-affected zone (HAZ), pulsed MIG welding process is used. The results showed that an increase in the heat input leads to a decrease in the cooling rate and an increase in the primary dendrite arm spacing in the weld metal. In the HAZ, grain size increases due to recrystallization and grain growth, with increasing the heat input. The results of tension and microhardness test show decreasing the mechanical properties in the HAZ. The weld metal in all samples exhibits a less resistance to pitting corrosion than the base metal and increasing the heat input do not have noticeable effect on the corrosion behaviors of the weld metal. However, by increasing the heat input, corrosion diagrams of the HAZ shift to the low currents which indicates an improvement in the corrosion behavior, due to the slower cooling rate and further dissolution of b phase.

In the present work, NiFe2O4 powder was synthesized by plasma arc discharge method. A mixture of iron and nickel powders with the appropriate molar ratio was prepared and formed into the cylindrical shapes. The synthesis process was performed under the air atmosphere with the pressure of 1 atm and the applied arc current of 400 A. After establishing an arc between the electrodes, the as-synthesized powders were collected and their structure, microstructure and magnetic properties were examined by XRD, FESEM and VSM, respectively. The XRD results show that the nickel ferrite with a spinel structure is successfully formed. The microstructural examinations reveal that the average particle size is about 120 nm. Saturation magnetization and coercivity of the as-synthesize powders are found to be 43.82 emu/g and 99 Oe, respectively.

In this study, Astsloy85Mo powder metallurgy steel specimens were surface melted using Tungsten Inert Gas (TIG) process. The effects of different parameters of the process on the microstructure, hardness, and wear resistance of the melted surfaces were studied using optical and scanning electron microscope equipped with EDS, Vickers hardness unit and pin on flat wear test machine. Surface melting resulted in structural refinement and the hardness of the melted layers reached to the values of up to 800 HV10, more than five times of that of the base PM steel which was about 150 HV10. Moreover, surface melting reduced the wear rate to 100 times lower than that of the base steel. It can be concluded that TIG can be used effectively for surface melting to improve the wear resistance of the Astaloy 85Mo powder metallurgy steel surface.

structural materials. On the other hand, graphite can easily react with oxygen even at temperatures as low as 400oC. The graded silicon carbide (SiC) characterized by compositional gradation over microsopic distances, is considered to be the most promising coating material. In this paper, the pack cementation technique was used to make a graded SiC coating on graphite at 1600oC. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis display that the coating obtained by the pack cementation is a dense structure consisting α-SiC and b-SiC with functionally graded structure. the mechanism of formation of SiC coating on graphite is explained by thermodynamics analysis and chemical equilibrium calculations using HSC Chemistry software 6.0.The reaction-path mechanism indicates in the early stages of the process, SiO and CO gas species can be formed during Al2O3 reaction with Si and C and at two reaction Si+C=SiC and SiO (g)+2C=SiC+CO (g) can be considered as main reactions for SiC coating formation. It was found that the composition of raw materials has not marked effect on the microstructure and property of SiC coating. In fact, this paper proposes a method for the analysis and simulation of pack cementation reactions using HSC Chemistry software package. The results of the simulation are verified by experimental results.

In the present study, optimization parameters for the tape casting is studied to produce a Yttria-stabilized zirconia (YSZ8) thick films for using as solid electrolytes in solid oxide fuel cell (SOFC). Taguchi designed experimental procedure was used to consider the characteristics of the slurry, such as the percentage of solid phase, binder and the ratio of plasticizers to the binder. The results indicated that the percentage of solid-phase have the greatest influence on the slurry viscosity and green density. Therefore the slurry containing the maximum possible solid-phase with the proper percentage of binder and plasticizers which provides an acceptable viscosity, can be selected as the proper slurry. This slurry is used to produce a relatively dense tape which sintered at 1450oC for 2 h. The density of sintered tape was 97% of theoretical density. The ionic conductivity of the sintered sample was determined with impedance measurement in temperature range of 300 to 800oC. The measured conductivities were 1.088×10-5W-1.cm-1 at 300oC and 2.27×10-2W-1.cm-1 at 800oC.

In this study WC-Co coating was produced on low carbon steel substrate by electrolytic plasma processing (EPP). EPP is an emerging, environmentally friendly surface engineering technology. Cermet coatings can improve tribologycal properties of steel substrates. Cermet coatings which were provided by EPP not only have suitable surface features, but also have unique morphology which causes good adhesion to the substrate. The samples were coated by applying direct current and voltage of 110 volt. Morphology and cross-sectional observations and also wear path were studied by scanning electron microscope (SEM). Results of energy dispersive spectroscopy (EDS) indicate the presence of tungsten, carbon, cobalt and iron in the coating. Wear tests have been carried out with a pin on disc device and SAE52100 pin. Based on the results of this test, samples which were coated with WC-Co, show higher wear resistance and lower friction coefficient (0.7). Worn path images reveal that the dominant mechanism of wear is abrasive.

Tea compost was assessed as a biosorbent by using a continuous up-flow fixed-bed column for removing of Pb2+, Co2+, Ni2+ and Cu2+ ions from aqueous solutions. The effects of various parameters such as pH, contact time, metal concentration, flow rates and amount of adsorbent on the process was investigated. The adsorption efficiency was found to be pH dependent, increasing by increasing of pH. Maximum removal of ions was obtained at pH=5 for tea compost. The equilibrium time was attained after 30 min and desorption studies was performed using diluted HNO3 (1 M) from tea compost. The results illustrated that adsorbed metal ions could be recovered under acidic conditions. Investigations the kinetics of the process were performed considering pseudo second-order model. This model predicted chemiosorption as the adsorption mechanism of the process. In addition, Thomas, Bohart-Adams and Yan kinetics models were studied The Thomas and Bohart-Adams model appeared to describe the experimental results better. Langmuir, Freundlich and Temkin models were tested for describing the equilibrium data. The Freundlich isotherm illustrated the best description of the cobalt, copper, nickel and lead adsorption mechanisms on tea compost. Results showed is more the in 30 min efficiency of tea compost column biofilter in removing heavy metals that can be remove than 95%.

In this study, the early stages of copper electrode position on molybdenum substrate from slightly acidic electrolyte were studied by cyclic voltammetry (CV) and chronoamperometry. The electrochemical deposition of copper on molybdenum substrate was investigated from the view point of thermodynamic, kinetic, and nucleation and growth mechanism. According to the CV analysis, the electrodeposition of copper on molybdenum substrate was determined to be irreversible process with diffusion controlled and it was confirmed by Randles-Sevcik equation. Diffusion coefficient of copper species at pH=3 and 4 was determined by Randles-Sevcik and Cottrel equations and their results were in agreement with each other. Using Scharifker-Hills model, the current transients of copper were analyzed. The copper nucleation mechanisms were evaluated as a function of solution pH and deposition potential. It was found that at pH=3 and 4, the nucleation mechanism of copper on grounded substrate was mixed, while with increasing the pH and potential, the nucleation mechanism shifts toward 3D instantaneous. Soaking of substrate in NH3 and then HCl solution after grounding did not change the nucleation mechanism. Etching the substrate in solution containing H2SO4, HNO3 and HCl after grounding changed the nucleation mechanism from 3D instantaneous to 3D progressive.

According to the industry’s need to an appropriate bonding process for components made of AISI 321 austenitic stainless steel, which is used in power-plant parts such as turbines, transient liquid phase (TLP) bonding of AISI 321 steel using MBF-30 and MBF-20 interlayers was studied in this research. TLP bonding was performed in a vacuum furnace at 1050, 1100 and 1150oC for 30-120 minutes. The microstructural studies were conducted on the joints using an optical microscope and an scanning electron microscope (SEM). Phase analysis of the joints was also performed a SEM/EDS and XRD system. To investigate the distribution of elements across the joints, line scan analysis was used. The shear strength test and the microhardness measurement test were conducted on the joints, in order to study the joints’ mechanical properties. The minimum time or complete isothermal solidification at 1050, 1100 and 1150oC was obtained as 75, 45 and 30 minutes, respectively. At the incomplete isothermal solidification condition, Fe-B, Cr-B, Ni-Si and Ni-B phases were observed at the joint centerline and diffusion affected zone (DAZ). With increasing bonding temperature and time, more homogenous joint, lower hardness at the different zones of the joints and higher shear strength were obtained. The maximum shear strength for MBF-30 interlayer was obtained as 99 and 98 percent of that of the base metal, and for MBF-20 interlayer was obtained as 95 and 94 percent of that of the base metal, respectively.

A novel nanocomposite based on graphen oxide and beta cyclodextrin molecules was constructed and used for electrochemical detection of curcumin, chlorpromazine and clomipramine. The obtained beta cyclodextrin- graphen nanocomposite was characterized by Fourier Transform infrared (FTIR) spectroscopy, high resolution transmission electron microscopy (HRTEM) and electrochemical impedance spectroscopy (EIS). FTIR results showed that beta cyclodextrin molecules are attached to graphene sheets with hydrogen bonding. HRTEM images showed single layers of graphene oxide nanosheets and the homogenous distribution of betacyclodextrin molecules on to the surface of graphen oxide sheets. The fabricated sensor represents good electrochemical response toward oxidation of these drugs via differential pulse voltammetry. For curcumin, chlorpromazine and clomipramine oxidation peak current was recorded at 0.48, 0.61 and 0.31 V.

This paper reports the successful synthesis of nano structured forsterite (Mg2SiO4) scaffold with high compressive strength for tissue engineering application. Forsterite slurry was prepared and pre-cut foams were immersed in the slurry for 5 min. The saturated foams were then annealed at various times and temperatures using the two step sintering method. The compressive strength and porosity of the scaffolds were in the range of 0.03-24.16 MPa and 58-88% depends on the heat treatment process, respectively. The J samples consisted of grains in the range of 24 to35 nm and micron size pores that could be detected by SEM observation.

Magnesia-doloma refractories are alkali products from sintered (or fusion) doloma and magnesia fusion), which have 50-80 wt. % MgO. These refractory have many advantages such as high corrosion resistance against slag, high temperature performance, ability to produce clean meet, and cost-effective (due to the abundance of dolomite and magnesite ores in Iran). However, the use of this type of refractories has been faced with restrictions due to poor hydration resistance in various industries. In this study, the effect of adding zirconium oxide nanoparticles on microstructure and hydration resistance of magnesia – doloma refractories containing 35 wt. % CaO is evaluated. Cylindrical samples were pressed under pressure 90MPa, and after it were dried and fired at 110oC for 24 h and, heated t0 1650oC with 5min /oC the for 3 h. Results show that the positive effect of adding zirconium oxide nanoparticles on the sintering temperature samples, due to the larger atomic radius of Mg than Ca thus lower the bond strength of Mg-O tend replacement Ca2+ with Zr+4 cations network with CaO greater than Mg2+ in MgO networks and the formation of calcium zirconate phase (CaZrO3). According to the result it can be found thet in doloma free CaO reduced by creating (CaZrO3) phase, as well as cavities formed by replacing the cationic in the network, increased the diffusion and sintering process which it led to creates a more dense structure and hydration resistant improvement.

In this research, the ARB process was used to produce Cu/Al/Al2O3 nano-composite. For this purpose, the rolling process was performed in multistep. In the beginning step, the surface of Al and Cu plates were prepared and then in the second step, three pieces of Al plates were put between four pieces of Cu plates and the boundary of plates was filled with alumina powder. In the third step, these layers were shaped as sandwich layers and rolled. The sandwiches were then cut into half and surface treatment was performed on them. Then, two halves of the composite were overlaid together and then rolled again. The rolling process was conducted for nine cycles. Microstructure and mechanical properties of each composite were analysed during each rolling cycle. Microstructural analysis was carried out via optical microscopy (OM) and scanning electron microscopy (SEM). Mechanical properties at various cycles were evaluated by tensile and hardness tests. Phase analysis of the samples was performed by using X-ray diffraction (XRD) analysis. Additionally, the corrosion behaviour of the composites was investigated at different cycles. The obtained results showed that by repeating the rolling cycles, the thickness of reinforced aluminium layer decreased and this layer was distributed in the final cycle as a consequence of fracture. In addition, Al2O3 powder was uniformly distributed into the matrix. By increasing the number of the cycles, the structure of the composite was crashed and approximately decreased to 31.26 nanometers in the final cycle. By using the ARB process, the amount of ultimate tensile strength and hardness of composite increased to 420 Mpa and 140 HV as compared with the aluminium plates (252 MPa and 55 HV), respectively. The dominant form of corrosion in this composite is pitting corrosion and thus, the resistance of products prepared via the ARB process against the pitting corrosion is low.