Papers by Author: M. Heydarzadeh Sohi

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Authors: M. Heydarzadeh Sohi, Shahin Khameneh Asl, Kazuyuki Hokamoto, M. Rezvani
Abstract: Five types of tungsten carbide based powders with different chemical compositions (WC-12Co, WC-17Co, WC-10Ni, WC-10Co-4Cr and WC- 20Cr-7Ni) were deposited onto ST37 mild steel substrate using high velocity oxy fuel (HVOF) spray technique. The feedstock powders and sprayed coatings were studied by using X-ray diffraction (XRD), and differential thermal analyzing (DTA). The results were shown during HVOF thermal spraying, WC-M powders become partially melted before being sprayed on the surface of the substrate with supersonic speed. In these types of coatings, the crystallographic structures are normally non equilibrium, because the cooling rates of the deposited splats are very high due to the cold substrate acting as a thermal sink. These partially melted powders are then rapidly solidified to an amorphous phase. XRD analysis showed that the amorphous phase was existed in all of the as sprayed coatings. The amorphous phase in WC-12Co, WC-17Co and WC-10Ni coatings was transformed to crystalline phases by heat treatment at high temperature. Heat treatment of these coatings at high temperature also resulted in partially dissolution of WC particles and formation of new crystalline phases. In cobalt base coatings, the new phases were eta carbide phases like Co6W6C and Co3W3C but in WC-10Ni coating a NiW intermetallic phase was formed. Heat treatment of WC-10Co-4Cr and WC-20Cr-7Ni coatings did not change the amorphous phases in these coatings. Differential thermal analysis of cobalt containing coatings revealed an exothermic reaction at approximately 880°C. This exothermic reaction may be related to the transformation of the amorphous phase to eta phases. On the contrary, DTA analysis of feedstock powders of these coatings showed an endothermic reaction at approximately 1000°C. DTA analyses of nickel containing cermets also showed similar results. Differential thermal analysis of chromium containing cermets did not show any noticeable exothermic or endothermic reactions.
Authors: M. Heydarzadeh Sohi, Mahmoud Nili-Ahmadabadi, A. Bahrami Vahdat, A. Amirsadeghi
Abstract: In this investigation the role of alloying elements on austemperability of heavy section ductile irons was studied. Four different chemical compositions were chosen in a way to specify an optimal chemical composition with suitable austemperability. Austempering was carried out at 315 and 350oC for 1 hour on specimens prepared from cast Y-blocks with 75 mm thickness. Metallographic examinations and hardness tests indicated that thickness of bainitic layer was positively dependant on the amount of the alloying elements which deferred pearlitic transformation in TTT diagram to the longer time. In addition, by increasing the amount of alloying elements, the morphologies of ferrite in bainitic structure changed from featherlike to acicular. According to the results of this study, in order to achieve a full bainitic structure (in the specimens whit 75mm thickness), the optimal amounts of alloying elements were: 0.35 % Mn, 0.22 % Mo, 1.1-1.4% Ni and 0.6% Cu. In addition, regarding to the thick sections of Y-blocks, graphite degeneration defect was also studied, and it was noticed that this defect could be completely eliminated by adding 50ppm of antimony.
Authors: Soheila Kharratian Khameneh, M. Heydarzadeh Sohi, Abolghasem Ataie, Saeed Mehrizi
Abstract: A study of the incorporation of barium hexaferrite nanoparticles into a CoFe matrix by means of electrodeposition over brass substrates has been performed. Barium hexaferrite nanoparticles were prepared by co-precipitation route using solution of iron and barium nitrates with a Fe3+/Ba2+molar ratio of 8, by addition of NaOH with a OH-/NO3- molar ratio of 2. X-ray diffraction (XRD) results indicated that in a sample synthesized from aqueous solution and annealed at 900 °C for 1 hour, BaFe12O19 was the dominant phase. Field emission scanning electron microscopy (FE-SEM) showed plate-like particles of barium hexaferrite by mean diameter of 300 nm and thickness of 45 nm. CoFe-BaFe12O19 nanocomposite thin films were then electrodeposited froma Co-Fe bath containing the barium hexaferrite particles obtained in the first stage of this work. Finally, FE-SEM equipped with energy dispersive spectroscopy (EDS) analyzer and XRD analysis was applied on the deposited films, to confirm presence of the nanoparticles in the film. The average crystallite size of the deposits was around 30 nm. It was also noticed that increasing the concentration of the particles in the electroplating bath, caused a rise in the BaFe12O19 content of the deposits but had no significant effect on the composition of the CoFe matrix.
Authors: Hassan Ghorbani, M. Heydarzadeh Sohi, Mohammad Javad Torkamany
Abstract: In the present work Ti-6Al-4V titanium wrought alloy was initially sprayed with TiC-15 wt% Ni powder, before being liquid phase surface treated by pulse Nd-YAG laser. Microstructure, chemical composition and phase analysis and hardness of the treated layers were studied by using field emission scanning electron microscope (FE-SEM), energy dispersive spectrometer (EDS), X-ray diffraction analysis (XRD) and micro-hardness test respectively. The result showed that the treated layers had ultrafined dendritic structure containing nanosize TiC particles and their hardness were as high as 982 HV0.03 respect to 350 HV0.03 for the base material.
Authors: Shahin Khameneh Asl, M. Heydarzadeh Sohi, Kazuyuki Hokamoto, Mitsuhiro Matsuda, Ryuichi Tomoshige, Minoru Nishida
Abstract: In this work, WC-17Co powder was thermally sprayed onto mild steel using HVOF spray technique. The coated specimen was heat treated at 1100°C in a vacuum chamber and was then studied by using transmission electron microscopy (TEM). Post heat treatment resulted in recrystallization of the amorphous phase, formed during thermal spraying, into low carbon eta phase like Co6W6C. TEM results of the heat treated specimens showed that these new nucleated eta phases had very clear crystallographic structure without any crystalline defects. Heat treatment could also transform high carbon carbides like WC and W2C in the as sprayed samples to high carbon eta phases like Co3W3C. High density of dislocations and staking faults noticed in TEM of these phases might be an indication of possible shear mechanism in formation of these carbides.
Authors: M. Heydarzadeh Sohi, S. Shahbazi, A. Halvaee
Abstract: In this study tungsten inert gas (TIG) surface melting of pre- plasma sprayed WC-14%Co low carbon steel has been studied. Surface melting was performed under different heat inputs by using various TIG parameters including intensity and kind of current. Microstructure and microhardness of surface alloyed specimens were then studied. Eutectic structures containing tungsten-rich carbides were shaped in a matrix including martensite lath, when high heat input was used. Decreasing at heat input affected the microstructure of the alloyed layers, and high amount of faceted tungsten-rich carbides (Fe3W3C) were formed in fairly low heat input. Microhardness of melted layers highly improved in comparison with that of the substrate.
Authors: Arsalan Ravanbakhsh, Fereshteh Rashchi, M. Heydarzadeh Sohi, Rasoul Khayyam Nekouei
Abstract: In this study, the ZnO thin film was synthesized by means of anodic oxidation method. A basic solution containing NaOH and NH4Cl as additive was used for the process. Effect of time and voltage on the microstructure of the obtained thin film has been studied. Characterization has been performed using grazing incidence X-ray diffraction (GIXD), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). Nanostructured thin film has been obtained with different morphologies according to different process parameters. FESEM analysis indicated that as the process time increases, the morphology of the film changes from grooved surface into flaky porous structure. It was also evident that hexagonal shaped simonkolleite formed during the process which was then transformed into zinc oxide and zinc chloride by heat treating.
Authors: Shahin Khameneh Asl, M. Heydarzadeh Sohi, S.M.M. Hadavi
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