Showing 64 results for Ai
A. Kermanpur, H. Ebrahimiyan, A. Heydari, D. Heydari, M. Bahmani,
Volume 14, Issue 4 (12-2017)
Abstract
Formation of stray grain defects particularly around re-entrant features of the turbine blade airfoils is one of the major problems in directional and single crystal solidification processes. In this work, directional solidification tests of the GTD-111 Ni-based superalloy were conducted at different withdrawal velocities of 3, 6 and 9 mm.min-1 using various stepped cylindrical and cubic designs. The process was also simulated using ProCAST finite element solver to characterize the crystal orientations. The phase transformation temperatures of the superalloy were estimated by the differential scanning calorimetry test. A process map was developed to predict the formation of stray grains in the platform regions of the stepped cylindrical and cubic specimens using the experimentally-validated simulation model. The process map shows critical values of the platform size, withdrawal velocity and initial sample size for the stray grain formation. The withdrawal velocity, platform size and initial sample size all had an inverse effect on the formation of stray grains.
A. Eivani, S.h. Seyedein, M. Aboutalebi,
Volume 15, Issue 1 (3-2018)
Abstract
In this research, samples of AlMg0.7Si aluminum alloy are deformed up to three passes using equal channel angular pressing (ECAP). Formation of a sub-micron structure after three passes of ECAP is demonstrated. Microstructural stability of the samples is investigated at temperatures of 300-500 °C. At 300 °C, fine recrystallized structure forms after 10 min which remains stable when the annealing proceeds up to 18 hrs. However, at 350 °C and higher, the microstructure is quite unstable. Even by 10 sec annealing, the samples exhibit recrystallized structure which turned to abnormal grain growth when temperature enhances to 500 °C and time up to 300 sec.
R. Jafari, Sh. Mirdamadi, Sh. Kheirandish, H. Guim,
Volume 15, Issue 3 (9-2018)
Abstract
In this research, the objective was to investigate the stabilized retained austenite in the microstructure resulting from the Q&P heat treatment since the primary goal in Q&P is to create a microstructure consists of stabilized retained austenite and martensite. For this purpose, a low-alloy steel with 0.4wt. % carbon was treated by quench and partitioning (Q&P) process. The Q&P was conducted at different quench temperatures to obtain a considerable amount of retained austenite, while partitioning temperature and time were kept constant. Through analysis of the XRD profiles, volume percent, carbon concentration, and lattice parameters of retained austenite and martensite were calculated. At quench temperature equal to 160°C, 12vol.% austenite was stabilized to the room temperature, which was the highest amount achieved. The microstructural observations carried out on selected samples, revealed that retained austenite has a nanoscale particle size, about 200nm. Distinguishing retained austenite in the SEM micrographs became possible by utilizing SE2 signals via the difference in phases contrast. Two types of morphology, film-like and blocky type, were identified by means of TEM and TKD and a schematic model was proposed in order to explain these morphologies
A. Ait Yala, N. Demouche, S. Beddek, K. Hamid,
Volume 15, Issue 4 (12-2018)
Abstract
Repairing a crack in a structure consists in reducing crack’s tips stresses by transferring loads trough a bridge made of the composite patch and the adhesive. This operation is impacted by four factors: shear modulus of the adhesive, the composite patch’s Young module and the thicknesses of these two materials. The design of experiments method allowed us to determine, the weight of each of the four factors and their interactions as well their best combination to obtain an efficient and lasting repair. The constraints relative to the stiffness ratio and the shear strain were taken into consideration in order to determine the best configuration that allowed the minimization of K.
M. Karimi Sahnesarayi, H. Sarpoolaky, S. Rastegari,
Volume 16, Issue 2 (6-2019)
Abstract
In this study nanosized TiO2coatings on the 316L stainless steel substrate were prepared by means of dip-coating technique in which thickness of the coating layer increased byrepeating the coating cycles in two different routes: (I) dipping and drying,respectively, were repeated one, three and five times and finally the dried coated sample was heat treated (single); (II) multiple heat treatment performed after each dipping and drying cycle, respectively.The structural, morphological and optical characterizations of coatings as well as thickness of coatings were systematically studied.The photocatalytic activity of the various TiO2 coatings was investigated based on the degradation of an aqueous solution of Methyl orange.Moreover, thecorrosion protective properties of coatings were evaluated in both dark and UV illumination conditions based on the obtained polarization curves. The results indicated 1.75 times improvement in photocatalytic reaction rate constant, a two orders of magnitude decrease in corrosion current density in dark condition and about 140 mV electrode potential reduction under UV illumination with optimum coating preparation procedure, repeating the cycle from dipping to heat treatment three times, than the sample prepared with one time coating and heat treatment since this procedure provided not only high thickness and defect-free coating but also transparent one.
H. Fathi, B. Mohammad Sadeghi, E. Emadoddin, H. Mohammadian Semnani,
Volume 16, Issue 3 (9-2019)
Abstract
Abstract
In the present research, the behavior of 304L austenitic stainless steel in the deep drawing process has been studied at the room temperature through experimental and finite element simulation method. Magnetic method calibrated by XRD was used to measure induced-martensite. Martensite volume fraction in the various portion of the deep drawn cup under optimum Blank Holder Force (BHF) and in the rupture location was evaluated. Findings of the present study indicated that higher martensite volume fraction occurred in the flange portion in the drawn cup due to higher strain and stress concentration in this area. Also, rupture happened at the arc portion of the wall of drawn cup with higher blank diameter due to higher strain, work hardening and martensitic transformation. Both experimental and simulation results showed that maximum LDR of 2 obtained in the forming process. All experimental procedures were simulated by LS-DYNA software, employing MAT_TRIP, and experimental results were in good agreement with the FE simulation.
M. Hoghooghi, O. Jafari, S. Amani, G. Faraji, K. Abrinia,
Volume 16, Issue 4 (12-2019)
Abstract
Spread extrusion is a capable method to produce different samples with a wider cross-section from the smaller billets in a single processing pass. In this study, dish-shaped samples are successfully produced from the as-cast cylindrical AM60 magnesium alloy at 300 °C, the mechanical properties and microstructural changes of the final specimens are precisely evaluated. Due to the high amount of plastic strain, which is applied to the initial billet during the material flow in the expansion process, grain refinement occurred as a result of recrystallization and subsequently good mechanical properties achieved. Therefore, mean grain size reduced from 160 µm to 14 µm and initial equiaxed grains changed to the elongated ones surrounded by fine grains. Also, microhardness measurements indicate that hardness increased from 51 Hv to 70 Hv. Some fluctuations were also observed in the hardness profile of the sample which was mainly related to the bimodal structure of the final microstructure. Good mechanical properties, fine microstructure, and also the ability to produce samples with higher cross-section make the spread extrusion process a promising type of extrusion.
H. Jafarian, H. Miyamoto,
Volume 17, Issue 1 (3-2020)
Abstract
In the present work, accumulative roll bonding (ARB) was used as an effective method for processed of nano/ultrafine grained AA6063 alloy. Microstructural characteristics indicate considerable
grain refinement leading to an average grain size of less than 200 nm after 7 ARB cycles. Texture analysis showed that 1-cycle ARB formed a strong texture near Copper component ({112}<111>). However, texture transition appeared by increasing the number of ARB cycles and after 7-cycle of ARB, the texture was mainly developed close to Rotated Cube component ({100}<110>). The results originated from mechanical properties indicated a substantial increment in strength and microhardness besides a meaningful drop of ductility after 7 ARB cycles.
M. Azadi, M. Ferdosi, H. Shahin,
Volume 17, Issue 1 (3-2020)
Abstract
In this paper, the effects of solutioning and various aging heat treatment processes on the microstructure, the hardness and electrochemical properties of a duplex stainless steel (DSS) were studied. The evaluation of the microstructure and phase compositions were carried out by the optical microscopy (OM) and the X-ray diffraction (XRD), respectively. Electrochemical behaviors of specimens were evaluated by both potentiodynamic polarization and electrochemical impedance spectra (EIS) tests at temperatures of 25 and 60 ºC. The obtained results showed that the solutioning heat treatment increased corrosion rates with respect to the blank specimen. The aging process at 490 ºC for 20 hrs increased the volume percent of the carbide phase to the highest value (25.1%) which resulted in an increase of the hardness value to 170 VHN. The specimen which was aged at 540 ºC for 10 hrs with the Cr7C3 size of 22.8 µm, exhibited the higher corrosion resistance at both temperatures of 25 and 60 ºC with respect to other aged specimens. In addition, the temperature of 60 ºC promoted the anodic reactions in 3.5 wt% NaCl solution which decreased impedance modulus values significantly. Consequently, the carbide size was more effective parameter than the carbide content in predicting electrochemical behaviors of such alloys.
S. Mortezaei, H. Arabi, H. Seyedein, A. Momeny, M. Soltanalinezhad,
Volume 17, Issue 3 (9-2020)
Abstract
Dynamic Recrystallization (DRX) is one of the likely mechanisms for fine-graining in metals and alloys. The dynamic recrystallization (DRX) phenomena occurs in different thermo-mechanical processing (TMP) conditions for various metallic materials. DRX depends on various materials and thermo-mechanical parameters such as temperature, strain rate, strain, stress and initial microstructure. in the present study, the restoration mechanism of the 17-7PH stainless steel has been investigated using a hot compression test under different conditions of thermo-mechanical treatment. The microstructural characteristics and the behavior of the hot deformation of the under study steel are investigated using flow curves and microstructure images obtained from optical microscopy. The results show that the maximum and steady state stresses are significantly affected by the strain rate and the deformation temperature. So that, the flow stress increases with decrease in the deformation temperature and increase in the strain rate. Microstructural studies confirm the occurrence of DRX as a restoration mechanism in the microstructure for the two phases of austenite and ferrite.
A. Kazazi, S. M. Montazeri, S. M. A. Boutorabi,
Volume 17, Issue 4 (12-2020)
Abstract
In the present study, austempering heat treatment was performed on compacted graphite aluminum cast iron with the chemical composition of 4.8%wt Al, 3.2%wt C, 0.81%wt Ni, 0.37%wt Mn, and 0.02%wt Mg. This study aims to investigate the effect of aluminum additions and removal of silicon on the kinetics of austempering transformation of Fe-3.2%C alloy. The cast samples were austenitized at 900 °C for 120 min and the isothermal austempering heat treatment was performed at 200 °C, 300 °C and 400 °C for 5, 30, 60, 120 and 180 minutes, respectively. Kinetics of this transformation was studied by X-Ray diffraction (XRD) analysis. The effect of temperature and time on the microstructure and hardness of the austempered samples was investigated and discussed. The presence of Al was seen to prolonged formation of the carbides from high carbon austenite, and that expanded the process window in the austempering transformation. Besides, the lower bainitic ferrite phase was observed in the austempered samples at 200 °C and 300 °C. Increasing austempering temperature to 400 °C changed the lower bainite to upper bainite structure. The volume fraction of austenite reached its maximum level (34.6 %) after austempering the samples at 400 °C for 30 minutes.
Mahnaz Mohammadzadeh Mianji, Hossein Sarpoolaky, Mehrnoush Shafiei Sararoudi,
Volume 18, Issue 1 (3-2021)
Abstract
Translucent porcelain with appropriate workability has been considered beneficial for light and shadow to be used in the production of ceramic artworks. In addition, using low firing temperature encourages more artists to use this body. The soft-paste cellulose composite porcelain is composed of similar amount of high Borax/Calcia leadless frit and Kaolin with 3% Vee gum T as a plasticizer. In order to increase workability and green strength, five units of soft-paste porcelain (SP) slip was mixed by one unit bleached bagasse pulp of sugar cane slip in volume and then cellulose containing soft-paste porcelain (CSP) slip was made. The samples were formed by hand, dried and then fired at the optimum temperature of 1120 for 5 hours. Results showed that the SP sample became self-glazed after firing while cellulose increased porosity in CSP. Microstructure analysis showed a large amount of glass phase, which improved translucency of the bodies. Moreover, mullite needle-shaped crystals were derived from the flux-penetrated clay because of less viscous molten body matrix. XRD results clearly showed that the fritted soft-paste porcelain consists of quartz, mullite, anorthite and albite in the fired state. Spectrophotometry showed that adding cellulose to the porcelain body slightly increased translucency in the wavelength ranges 400 to 500 nm.
Amir Mostafapour, Milad Mohammadi, Ali Ebrahimpour,
Volume 18, Issue 2 (6-2021)
Abstract
A full factorial design of experiment was applied running 36 experiments to investigate the effects of milling parameters including cutting speed with three levels of 62.83, 94.24 and 125.66 m/min, feed rate with three levels of 0.1, 0.2 and 0.3 mm/tooth, cutting depth with two levels of 0.5 and 1 mm and machining media with two levels, on surface integration properties of magnesium AZ91C alloy such as grain size, secondary phase percent, surface microhardness and surface roughness. In all cases, a fine grained surface with higher secondary phase sediment and microhardness obtained comparing the raw material. According to analysis of variance results, the most effective parameter on grain size, secondary phase percent and microhardness was cutting depth and the most effective parameter on surface roughness was feed rate. although the grain size in all machined samples was smaller than that of the raw material but due to the dual effect of cryogenic conditions, which both cool and lubricate and reduce the temperature and strain rate at the same time, the direct effect of this parameter on grain size was not significant. Also, the all interaction effects of parameters on grain size and microhardness were significant.
Mahdi Alishavandi, Mahnam Ebadi, Amir Hossein Kokabi,
Volume 18, Issue 2 (6-2021)
Abstract
Friction-Stir Processing (FSP) was applied on AA1050 Aluminum Alloy (AA) to find the highest mechanical properties among 28 combinations of the rotational and traverse speed (800-2000 rpm and 50-200 mm.min-1) and four different tool probe shapes (threaded, columnar, square and triangle). To this aim, the AA standard sheet went through a single pass of FSP. The 1600 rpm and 100 mm.min-1 with threaded tool probe was chosen as the best combination of rotational and traverse speed. Grain size at the Stirred Zone (SZ) was studied using Optical Microscopy (OM). The results showed that the SZ’s grain size was refined from 30 μm down to about 12 μm due to dynamic recrystallization during FSP. The processed sample exhibited improved hardness, yield stress, ultimate tensile strength, elongation up to 65, 80, 66, and 14%, respectively, compared to the annealed AA sample. Studying fractographic features by OM and field emission scanning electron microscope (FESEM) revealed a dominantly ductile fracture behavior.
Mala Siddaramappa, Haraluru Kamala Eshwaraiah Latha, Haraluru Shankaraiah Lalithamba, Andi Udayakumar,
Volume 18, Issue 4 (12-2021)
Abstract
Indium tin oxide (ITO) nanoparticles were synthesized by green combustion method using indium (In) and tin (Sn) as precursors, and Carica papaya seed extract as novel fuel. This paper highlights effect of tin concentration (5%, 10% and 50%) on microstructural, optical and electrical properties of ITO nanoparticles (NPs). The indium nitrate and tin nitrate solution along with the fuel were heated at 600 °C for 1 h in muffle furnace and obtained powder was calcinated at 650 °C for 3 h to produce ITO NPs. The above properties were investigated using XRD, FTIR, UV-Vis spectroscopy, SEM, TEM and computer controlled impedance analyser. The XRD, SEM and TEM investigations reveals the synthesized NPs were spherical in shape with an increase in average grain size (17.66 to 35 nm) as Sn concentration increases. FTIR investigations confirms the In-O bonding. The optical properties results revealed that the ITO NPs band gap decreased from 3.21 to 2.98 eV with increase in Sn concentration. The ac conductivity of ITO NPs was found to increase with increase in Sn concentration. These synthesised ITO NPs showed the excellent properties for emerging sensor and optical device application.
Saleheh Abbaspoor, Farhang Abbasi, Samira Agbolaghi,
Volume 19, Issue 2 (6-2022)
Abstract
Single crystals of double crystalline block copolymers of poly(ethylene glycol) (PEG)-b-poly(ε-caprolactone) (PCL) and PEG-b-poly(L-lactide) (PLLA) were grown from dilute solution in homo- and mixed-brush systems. Crystallization behavior of biodegradable one end-restricted crystallizable PCL and PLLA chains in homo- and mixed-brush nanostructures were investigated. Chemical and physical circumstances of crystallizable brushes were altered. Physical environment was adjusted by amorphism/crystallinity and rigidity/flexibility of neighboring brushes. Chemical environment was manipulated by interaction and miscibility of various brushes. Distinct single crystals were grown with mixed-brushes of amorphous-crystalline (polystyrene (PS), poly(methyl methacrylate) (PMMA), PCL and PLLA, double crystalline (PCL/PLLA), and rod-crystalline polyaniline (PANI)/PCL or PLLA. Surrounding was only effective on hindrance or nucleation commencement of crystallization for crystallizable brushes and had no effect on crystallization features. Novel three-layer fully single crystalline nanostructures, whose characteristics were fixed via changing the crystallization temperature, were also developed. For long crystallizable tethers, crystallization increased both brush and substrate thicknesses.
Nur Mohammad Hosseini, Zahra Bahri, Asghar Azizi,
Volume 19, Issue 4 (12-2022)
Abstract
The beneficiation of coal tailings is usually difficult by common oily collectors in the flotation process, so
it is necessary to use a suitable method for clean coal recovery from coal tailing dams. Thus, this study was aimed
to investigate the behavior of dissolved air flotation by zero prewetting time for the clean coal recovery and to
optimize the conditions of zero prewetting time for an effective flotation. In this regards, the effects of the process
parameters, i.e., pH, frother type, collector type on the rougher flotation recovery of coal tailings were assessed and
optimized. Additionally, Fourier transform infrared (FTIR) spectroscopy was used to understand the functional
groups of oily collectors on the surface of floated products. The findings indicated that the frother type and the
interactive effects between the type of frother and collector had the most effect on the performance of flotation. It
was also found that under the optimal conditions (150 g/t Methyl isobutyl carbinol, 1500 g/t gas oil, and pH 4), the
combustible recovery, yield reduction factor, and flotation efficiency index of coal reached to 67.79%, 0.056%, and
37%, respectively. Meanwhile, the FTIR analysis confirmed that the less adsorption of gas oil collector occurred in
the presence of SDS (Sodium dodecyl sulfate) as frother due to the interaction of SDS and collectors
Sravanthi Gudikandula, Ambuj Sharma,
Volume 19, Issue 4 (12-2022)
Abstract
The lean duplex stainless steels (LDSS) have excellent features due to the microstructural phase
combination of austenite and ferrite grains. These steels have low Ni and Mo contents which can reduce the cost
and stabilize the austenite fraction in the microstructure. In recent years, welding is used to enhance the
microstructural behaviour of LDSS. In this paper, Gas tungsten arc welding (GTAW) was performed on LDSS
S32101 with different heat energy inputs and varying welding currents. The influence of heat inputs (0.85 and 1.3
kJ/mm) on welded samples was investigated to study the microstructural behaviour, phase balance, and mechanical
& corrosion performance. The microstructures studies were carried out using an optical microscope, scanning
electron microscope and X-ray diffraction. The effect of Heat input led to the significant microstructural evolution
in weld metals with high austenite reformation. The microstructure of weldments consisted of inter-granular
austenite (IGA), grain boundary austenite (GBA) and Widmanstatten austenite (WA). Important mechanical
properties such as tensile strength and micro-hardness were investigated to understand the performance of
weldments. The polarization method was used to understand the corrosion behaviour of weldment in a 3.5% NaCl
solution. The experimental results showed enhanced properties of welds that could be suitable for industrial
applications.
Hassan Tarikhum, Basil A Abdullah, Furqan Almyahi, Mazin Mahdi,
Volume 20, Issue 2 (6-2023)
Abstract
In this study, poly(3-hexylthiophene) (P3HT) and fullerene Indene-C60 multi-adducts (ICxA) were blended to create a formulation as a solution and thin films, which were prepared under ambient conditions. The optical properties of various compositional ratios were studied using UV-Visible absorbance and photoluminescence (Pl) measurements. The energy gaps of the prepared thin films and solutions were determined, and their values increased with increasing fullerene ratio because of the isolation of P3HT chains from their neighbors. Intensity ratio (IC=C/IC-C) with a small value in addition to a low value of full width at high maximum (FWHM) of Raman spectra are associated with increased conformation and high aggregation of composition. Furthermore, according to X-ray diffraction (XRD) results the 1:0.8 and 1:0.6 ratios have the largest crystallite sizes in comparison to the other ratios. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels for blends by electrochemical measurements were determined, which are sandwiched between those of the pure materials. In ambient conditions, binary organic photovoltaic cells (OPVs) at different ratios of the photoactive layer were evaluated. The device with a ratio of 1:0.6 had the best performance, with power conversion efficiency (PCE) of 1.21 %, open circuit voltage (VOC) of 0.53 V, short circuit current density (JSC) of 5.71 mA.cm-2, and fill factor (FF) of 39.5 % at a small Vloss of 1.39 V.
Fabio Edson Mariani, Gabriel Viana Figueiredo, German Barragan, Luiz Carlos Castelleti, Reginaldo Teixeira Coelho,
Volume 20, Issue 3 (9-2023)
Abstract
Elevating component performance through advanced surface coatings finds its epitome in the domain of laser cladding technology. This technique facilitates the precision deposition of metallic, ceramic, or cermet coatings, accentuating their superiority over conventional methods. The application spectrum for laser-clad metallic coatings is extensive, encompassing critical components. Central to the efficacy of laser cladding is the modulation of laser parameters—encompassing power, speed, and gas flow—which decisively influence both process efficiency and coating properties. The meticulous calibration of these parameters holds the key to producing components endowed with refined attributes while ensuring the sustainable continuation of the process. As such, this study embarks on an empirical investigation aimed at transcending existing process limitations. It delves into the characterization of laser-clad WC-17Co coatings on AISI H13 and AISI 4140 steels. The importance of WC-17Co coatings lies in their capacity to enhance wear resistance, extend component life, reduce maintenance costs, and improve the performance of various industrial components across diverse sectors. On the other hand, the substrates have pivotal roles. AISI H13 is lauded for its exceptional hot work capabilities, while AISI 4140 steel is renowned for its robust strength and endurance. Through rigorous evaluation, the resultant deposited coatings offer crucial insights into the efficacy of manufacturing parameters. Employing a comprehensive suite of analytical techniques including laser confocal microscopy, Vickers microhardness assessment, and micro-adhesive wear testing, the study thoroughly characterizes the samples. The outcomes underscore the achievement of homogenous coatings marked by elevated hardness and exceptional wear resistance, thereby signifying a substantial enhancement over the substrate materials.
