Showing 111 results for Mo
M. Naseri, M. Alipour, A. Ghasemi, E. Davari,
Volume 15, Issue 1 (3-2018)
Abstract
One of the interesting state-of-the-art approaches to welding is the process of friction stir welding (FSW). In comparison with the fusion processes, FSW is an advantageous method as it is suitable for the non-fusion weldable alloys and polymeric materials joining. Regarding the materials pure solid state joining, it also provides joints with less distortion and enhanced mechanical properties. In the present work, a three-dimensional (3D) model based on finite element analysis was applied to study the thermal history and thermomechanical procedure in friction stir welding of high density polyethylene plate. The technique includes the tool mechanical reaction and the weld material thermomechanical procedure. The considered heat source in the model, includes the friction among three items: the material, the probe and the shoulder. Finally, the model was validated by measuring actual temperatures near the weld nugget using thermocouples, and good agreement was obtained for studied materials and conditions.
F. Farzan, H. R. Shahverdi, F. Malek Ghaeni,
Volume 15, Issue 2 (6-2018)
Abstract
Recently, wear resistant properties of metallic glasses has attracted a lot of interest. Because the surface of metallic glasses are prone to phase transformation, finding the effects of test condition on structure and wear behavior of metallic glasses is important. In this research, by using an automated electrospark deposition (ESD), a layer of Fe
51Cr
18Mo
7B
16C
4Nb
4 was deposited on AISI 316l stainless steel. Metallographic,
scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS) analyses of the coating were conducted for measuring the thickness and analyzing composition of the coating. X-ray diffraction (XRD), Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) investigations showed that the structure of the coating was amorphous. Ball on disc wear tests were conducted in dry and wet conditions and Ringer’s solution was chosen as the wetting agent. The wear test results showed that the coefficient of friction in dry condition was lower than the wet condition and wear modes were fatigue and corrosive wear in dry and wet conditions respectively. SEM and EDS analyses showed different features and elemental inhomogeneity on the surface of the dry wear track, which were not detectable in wet wear track. In addition, activation of diffusion process and formation of carbides and borides were observed on the wear track in dry condition.
S. Gholami Shiri, Y. Palizdar, . A. Jenabali Jahromi, Eduardo F. de Monlevade,
Volume 15, Issue 3 (9-2018)
Abstract
The relation between microstructure and the fracture mechanisms of δ-TRIP steel with different Nb-content has been investigated using complementary methods of light microscopy, SEM, EDS, EBSD, X-ray phase analysis and tensile test. The results revealed a close dependency between the presences of constitutive phases i.e. ferrite, bainite, retained austenite and martensite and the mode and characteristics of fracture. All samples revealed almost different fractography pattern which could be associated to the effect of Nb microalloying element. The different fractography patterns were consisted of dimple rupture, riverside and Wallner lines pattern. The proportion of the cleavage fracture in comparison of dimple rapture increased by increasing the Nb-content due to the increase of primary martensite in the microstructure.
H. Esfandiar, S. M. Hashemianzadeh, S. Saffary, S. Ketabi,
Volume 15, Issue 3 (9-2018)
Abstract
Gold nanoparticles have become common in many applications of biotechnology due to their specific properties. Shape and size are important attributes which affect their solubility in water. In this study, the outcomes of Monte Carlo Simulation for the solvation of gold nanorods in aqueous solution with the different radii, in terms of solvation free energy, are discussed. Simulation results show a negative solvation free energy for all the samples with radii of 4 to 9Å. The results show that the absolute values of solvation free energy for gold nanorods with smaller radius are larger, which indicate the dependency between the gold nanorods solvation and their radius.
M. Abbasalizadeh, R. Hasanzadeh, Z. Mohamadian, T. Azdast, M. Rostami,
Volume 15, Issue 4 (12-2018)
Abstract
Shrinkage is one of the most important defects of injection molded plastic parts. Injection molding processing parameters have a significant effect on shrinkage of the produced parts. In the present study, the effect of different injection parameters on volumetric shrinkage of two polymers (high-density polyethylene (HDPE) semi-crystalline thermoplastics and polycarbonate (PC) as a representative of amorphous thermoplastics) was studied. Samples under different processing conditions according to a L27 orthogonal array of Taguchi experimental design approach were injected. Effect of material crystallinity on the shrinkage of injected samples was investigated. Obtained results revealed that semi-crystalline thermoplastics have larger shrinkage values in comparison with amorphous thermoplastics. Shrinkages of injected samples were also studied along and across the flow directions. Results showed that the flow path can dramatically affect the shrinkage of semi-crystalline thermoplastics. However for amorphous thermoplastics, results showed an independency of obtained shrinkage to flow direction. Analysis of variance (ANOVA) results illustrated that cooling time was the most effective parameter on shrinkage for both PE and PC injected samples; followed by injection temperature as the second important parameter. The optimum conditions to minimize shrinkage of injection molded samples are also achieved using signal to noise ratio (S/N) analysis.
G. Chandraprabha, T. Sankarappa, T. Sujatha,
Volume 15, Issue 4 (12-2018)
Abstract
Polythiophene (PTh) and cobalt nanoparticles (Co-nps) were prepared by chemical oxidation and modified polyol processes respectively. Composites were made by mixing them in the proportions, PTh1-xCox; x = 0.1, 0.2, 0.3, 0.4, 0.5. Morphology of the samples has been studied by SEM technique. Dielectric properties with temperature and frequency as variables were investigated. Dielectric constant and loss factor decreased with frequency and increased with temperature. AC conductivity was estimated from the dielectric data. Ac conductivity decreased with increase of Co-nps in the composites which indicates that electrically insulating effect has been induced by Co-nps. Small polaron hopping mechanism is found to be the conduction mechanism operated. Activation energy for ac conduction decreased with increase of frequency and weight percent of Co-nps in the composites. Electric modulus was determined and its analysis leads to the estimation of dielectric relaxation time. Relaxation time decreased with increase of temperature for all the five composites. For the first time PTh-Co nanocomposites have been reported for dielectric properties and ac conductivity as a function of frequency and temperature.
A. Allahverdi, Z. Padar, M. Mahinroosta,
Volume 16, Issue 2 (6-2019)
Abstract
It is demonstrated that the addition of organo-modified Na-bentonite (OMB) particles to Portland cement mortar can promote its physical and mechanical properties. A series of experimental works on some important physico-mechanical properties of Portland cement mortars mixed with various dosages of hydrophobic OMB were performed. The obtained results confirm that the OMB provides a dense packing effect. An optimum replacement level of around 3.5% (by weight) at an increased water-to-cement ratio of 0.53 results in an almost 11.43% increase in 28-day compressive strength along with about 20.78 and 16.20% reductions in total volume of permeable pore space and water absorption, respectively. Also, at the optimum replacement level, an increase of about 2.72% is taken place in dry bulk specific gravity.
M. Akbarzadeh, M. Zandrahimi, E. Moradpur,
Volume 16, Issue 2 (6-2019)
Abstract
Molybdenum disulfide (MoS2) is one of the most widely used solid lubricants. In this work, composite MoSx/Ti coatings were deposited by direct-current magnetron sputter ion plating onto plain carbon steel substrates. The MoSx/Ti ratio in the coatings was controlled by sputtering the composite targets. The composition, microstructure, and mechanical properties of the coatings were explored using an energy dispersive analysis of X-ray (EDX), Xray diffraction (XRD), and nano indentation and scratch techniques. The tribological behavior of the coatings was investigated using the pin-on-disc test at room temperature. With the increase of doped titanium content, the crystallization degree of the MoSx/Ti composite coatings decreased. The MoSx/Ti coatings showed a maximum hardness of 13 GPa at a dopant content of 5 at% Ti and the MoSx/Ti composite films outperformed the MoSx films. Moreover, the films exhibited a steady state friction coefficient from 0.13 to 0.19 and the main wear mechanisms of the MoSx/Ti coating in air were abrasive, adhesive, and oxidation wear.
S. Mirzaei, H. Saghafian, A. Beitollahi, J. Świerczek, P. Tiberto,
Volume 16, Issue 3 (9-2019)
Abstract
In the present research, rapidly solidified Fe85.3B11P3Cu0.7 ribbons were prepared by melt spinning process. The microstructural variation as well as magnetic properties of the as-spun and annealed ribbons were characterized by X-ray diffraction (XRD), transmission Mossbauer spectroscopy and alternating gradient field magnetometer (AGFM). The results show two separated distinct exothermic peaks during heating resulting from the phase transition from amorphous to α-Fe and then to Fe3B, respectively. The study of magnetic properties in the amorphous and nanocrystalline states revealed that annealing the amorphous ribbons at 440˚C for 10 minutes gives rise to a significant increase in saturation magnetization (220 emu/g) which makes this alloy a good candidate for power applications.
E. Shahmohamadi, A. Mirhabibi, F. Golestanifard,
Volume 16, Issue 3 (9-2019)
Abstract
An accurate prediction of reaction kinetics of silicon nitridation is of great importance in designing procedure of material production and controlling of reaction. The main purpose of the present study is to investigate the effect of temperature on the kinetics of reaction bonded silicon nitride (RBSN) formation. To achieve this, nitrogen diffusion in the silicon nitride layer is considered as a reaction controlling factor and sharp interface method based on this theory is used to develop the analytical model. In the developed model, the variations in the size of silicon particles are calculated for the whole reaction. In the experimental phase, the extent of nitridation is measured for different reaction temperatures and 4 different reaction times and then, the occurrence of full nitridation is shown by EDS analysis. Furthermore, an analytical approach was established for describing the kinetics of compound formation and the performance of the developed model is evaluated through statistical analysis. There was good agreement between experimental data and predictions of the developed model which demonstrates the accuracy of considered presumptions and reaction mechanisms. An accurate prediction of reaction kinetics of silicon nitridation is of great importance in designing procedure of material production and controlling of reaction. The main purpose of the present study is to investigate the effect of temperature on the kinetics of reaction bonded silicon nitride (RBSN) formation. To achieve this, nitrogen diffusion in the silicon nitride layer is considered as a reaction controlling factor and sharp interface method based on this theory is used to develop the analytical model. In the developed model, the variations in the size of silicon particles are calculated for the whole reaction. In the experimental phase, the extent of nitridation is measured for different reaction temperatures and 4 different reaction times and then, the occurrence of full nitridation is shown by EDS analysis. Furthermore, an analytical approach was established for describing the kinetics of compound formation and the performance of the developed model is evaluated through statistical analysis. There was good agreement between experimental data and predictions of the developed model which demonstrates the accuracy of considered presumptions and reaction mechanisms.
A. Ostovari Moghaddam, A. Shokuhfar, A. Cabot,
Volume 16, Issue 4 (12-2019)
Abstract
Metal sulfides containing non-toxic and earth abundant elements have emerged as new environmentally friendly thermoelectric materials. In the present work, a new, fast and large scale route to synthesise bulk nanostructured Co1-xCuxSbS paracostibite is presented. Stoichiometric compositions of Co1-xCuxSbS nanoparticles with 0 ≤ x ≤ 0.08 were first processed by high energy ball milling for 3 h, and then annealed at different temperatures between 400 ºC to 650 ºC for 1 h. The phase transitions and diffusion process during annealing were thoroughly studied by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Agglomerated nanoparticles with sizes in the range from 40 nm to 80 nm were obtained after 3 h of ball milling, and remained below 100 nm after annealing and hot pressing. The thermoelectric properties of hot pressed samples, including the Seebeck coefficient (S), electrical conductivity (σ) and thermal conductivity (k), were measured from room temperature up to 723 K. All the samples exhibited a p-type semiconductor character at room temperature and underwent a transition from p-type to n-type conduction above 473 K. a maximum ZT value of 0.12 was obtained for Co0.06Cu0.04SbS4 at 723 K.
R. Latifi, S. Rastegari, S. H. Razavi,
Volume 16, Issue 4 (12-2019)
Abstract
In the present study, Zirconium modified aluminide coating on the nickel-base superalloy IN-738LC was first created by high activity high temperature aluminizing based on the out-of-pack cementation method. Then, Zr coatings were applied to simple aluminide coatings by sputtering and heat treatment in order to study the effect of Zr on the coating microstructure and oxide spallation. Microstructural studies were conducted by using scanning electron microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and x-ray diffraction (XRD) microanalysis. The results indicated that zirconium modified aluminide coating, like aluminide coating, has a two-layer structure including a uniform outer layer of NiAl and an interdiffusion layer in which zirconium is in a form of solid solution in the coating. Furthermore, the 300nm Zr-coated NiAl demonstrated an excellent scale adhesion, a slow oxidation rate and lower amounts of some other elements such as Ti and Cr in its oxide layer leading to a pure aluminide oxide layer.
A. Bahrami, F. Kazemi, J. Abdolahi Sharif,
Volume 17, Issue 1 (3-2020)
Abstract
Kinetic models are the most important instruments for predicting and evaluating the performance of flotation circuits. To determine the kinetic order and rate of flotation of a gilsonite sample, flotation experiments were carried out in both rougher and cleaner stages. Experiments conducted using the combinations of petroleum-MIBC, gas oil-pine oil, and one test without any collector and frother. Five first order kinetic models were applied to the data obtained from the flotation tests by using the Matrix Laboratory software. Statistical analysis showed that the classic first order model perfectly matched the rougher and cleaner results performed using petroleum-MIBC combination. The kinetic constants (k) were calculated as 0.04 (s-1) and 0.01 (s-1) for the rougher and cleaner, respectively. Rougher and cleaner tests without collector and frother also matched with the modified gas/solid adsorption and rectangular models with the k values of 0.05 (s-1), and 0.01 (s-1), respectively. The relationship between flotation rate constant, maximum combustible recovery and particle size were also studied. The results showed that the maximum flotation combustible recovery and flotation rate were obtained with an intermediate particle size both in the rougher and cleaner flotation processes. The combustible recovery and flotation rate in the rougher flotation process were higher than that in the cleaner flotation process.
A. Hasanvand, M. Pourabdoli, A. Ghaderi,
Volume 17, Issue 1 (3-2020)
Abstract
The main problem of cobalt oxide as a thermochemical heat storage material is its slow re-oxidation kinetics. In addition, redox (reduction and oxidation) behavior of as-received Co3O4 is degraded with increasing the number of redox cycles. To overcome this drawback, Al2O3 and Y2O3 were added to Co3O4 and effect of mechanical activation time (2, 4, 8, and 16 h) on the redox behavior (weight change value/rate, redox reversibility, reduction and re-oxidation values, and particle morphologies) of Co3O4-5 wt.% Al2O3 and Co3O4-5 wt. % Y2O3 composites was investigated using thermogravimetry method. The composites were studied by SEM, EDS, and X-ray map analyses before and after redox reactions. Results showed that increasing the mechanical activation time improves the redox kinetics of Co3O4-5wt. % Al2O3 in comparison with as-received Co3O4. Although, the alumina-containing samples, activated in short time showed the better redox kinetics than samples activated in long time. It was found that increasing the activation time to more than 8 h for alumina-containing samples reduces the redox kinetics due to decreasing the positive effect of Al2O3 in controlling the particle size growth and sintering. In the case of Co3O4-5wt. % Y2O3, an increase in activation time generally reduced the redox kinetics. As a result, redox reactions in a 16 h-activated Co3O4-5wt.% Y2O3 composite was completely stopped. In addition, results showed that weak performance of Co3O4-5 wt. % Y2O3 is related to intensive sintering and growth of cobalt oxide particles during redox reactions
E. Shahmohamadi, A. Mirhabibi, F. Golestanifard,
Volume 17, Issue 1 (3-2020)
Abstract
In the present study, a soft computing method namely the group method of data handling (GMDH) is applied to develop a new and efficient predictive model for prediction of conversion percentage of silicon. A comprehensive database is obtained from experimental studies in literature. Several effective parameters like time, temperature, nitrogen percentage, pellet size and silicon particle size are considered. The performance of the model is evaluated through statistical analysis. Moreover, the silicon nitridation was performed in 1573 k and results were evaluated against model results for validation of the model. Furthermore, the performance and efficiency of the GMDH model is confirmed against the two most common analytical models. The most effective parameters in estimating the conversion percentage are determined through sensitivity analysis based on the Gamma Test. Finally, the robustness of the developed model is verified through parametric analysis.
F. Hosseinabadi, A. Rezaee-Bazzaz, M. Mazinani, B. Mohammad Sadeghi,
Volume 17, Issue 1 (3-2020)
Abstract
An experimental–numerical methodology was used in order to study the microstructural effects on stress state dependency of martensitic transformation kinetics in two different TRIP800 low alloy multiphase steels. Representative volume elements extracted from actual microstructure have been utilized for simulating the mechanical behavior of mentioned steels. The mechanical behavior for each constituent phases required in the model has been taken out from those reported in the literature. A stress invariant based transformation kinetics law has been used to predict the martensitic phase transformation during deformation. Crystallographic and thermodynamic theories of martensitic phase transformation have been utilized for estimating the constant parameters of the kinetics law, in a recently performed investigation, but the sensitivity of the transformation to the stress state remained as an adjusting parameter. The results of the current work show that the stress state sensitivity of martensitic phase transformation in the investigated steels is microstructure-dependent and the value of this parameter is almost equal to half of the bainite volume fraction. Therefore, the volume fraction of bainite in the low-alloy multiphase TRIP800 steels can be used as a first postulation for the value of the martensitic phase transformation sensitivity to the stress state and the microstructure based model previously developed for calculating the mechanical behavior of the TRIP800 steels can be utilized as a virtual design tool for development of TRIP steels having specific mechanical properties.
M. Ghasemian Safaei, Dr. S. Rastegari, R. Latifi,
Volume 17, Issue 2 (6-2020)
Abstract
In this study, Si-modified aluminide coating on nickel-base superalloy IN-738LC was prepared using a pack cementation method with various powder compositions at 1050 °C for 6 h. The cyclic oxidation test was conducted at 1000 °C followed by cooling at room temperature for 200 h and 20 cycles. The effect of powder composition and the way of cooling on the coatings microstructure and oxidation behavior were studied. Investigations carried out using a scanning electron microscope (SEM), EDS analysis, and XRD. Microstructural observations revealed that the coating thickness of 293 and 274 µm was achieved in the case of using pure Al and Si powder and alloyed Al-20wt.%Si one in the packed mixture, respectively. It was also found that utilizing pure Al and Si powder with NH4Cl as an activator in the pack led to the formation of silicide coating, owing to the higher diffusion of Si, which showed superior cyclic oxidation performance.
S. Manafi, S. Joughehdoust,
Volume 17, Issue 2 (6-2020)
Abstract
In this research, calcium titanate (CaTiO3) hollow crystals have been successfully prepared via hydrothermal method. Titanium tetrachloride, calcium chloride dihydrate and potassium hydroxide were used as Ti, Ca and precipitating agent, respectively. The hydrothermal synthesis was performed at different temperatures and time durations. The negative amount of the Gibbs free energy shows the reactivity of the reaction at room temperature. Characterization of CaTiO3 was carried out using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The optimum condition for preparing CaTiO3 is the sample kept in an autoclave at 300 ℃ for 3 h that requires less energy and time which consists of a high degree of crystallinity. In this research, tetragonal CaTiO3 hollow crystals have been successfully prepared via hydrothermal method. TiCl4, CaCl2.2H2O, and KOH were used as Ti, Ca and precipitating agent, respectively. The hydrothermal synthesis was performed at different temperatures and time durations. Characterization of CaTiO3 was carried out using SEM, HRTEM, and XRD. The sample kept in the autoclave at 300 ℃ for 3 h well crystallized and required less energy and time for synthesis. The powder has a homogenous dispersity of crystals with the range of nanometer to micrometer sizes which makes it a good candidate as a photocatalyst material
S. Agbolaghi,
Volume 17, Issue 2 (6-2020)
Abstract
Confined and unconfined crystallizations of poly(3-hexylthiophene) (P3HT) were studied in the solution-grown supramolecules and melt-grown systems using a differential scanning calorimeter. The carbon nanotube (CNT) and reduced graphene oxide (rGO) and their functionalized (CNT-f-COOTh and rGO-f-TAA) and grafted (CNT-g-PDDT and rGO-g-PDDT) derivatives were employed to develop the samples. The absorbance, structure details via Scherrer formula, fusion enthalpy (ΔHm) and crystallinity (Xc) were measured in two distinct confined/unconfined crystallization environments. Although the functionalized-CNT/rGO precursors partially reduced the crystallite qualities with respect to the pristine CNT and rGO ones in the solution-grown supramolecules, they did not affect the structural properties in the melt-grown samples. Grafted carbonic materials could be considered as appropriate seeds for the arrangement of P3HTs in both solution and melt crystallizations. The best absorbances, larger and more compact crystals, and higher melting point, ΔHm, and Xc values were recorded for the pre-developed CNT-g-PDDT/P3HT stem-leaf (6.09–22.51 nm, 3.52–13.89 Å, 239.8 °C, 30.86 J/g and 83.40%) and rGO-g-PDDT/P3HT coarse-patched (5.96–20.76 nm, 3.57–13.95 Å, 237.6 °C, 29.13 J/g and 78.73%) supramolecules. Although the melt-grown CNT-g-PDDT/P3HT (201.4 °C, 215.3 °C, 16.22 J/g and 43.84%) and rGO-g-PDDT/P3HT (205.4 °C, 218.8 °C, 18.06 J/g and 48.81%) nanostructures were not as perfect as the respective solution-grown nano-hybrids, they were well-arranged with respect to the CNT/P3HT, CNT-f-COOTh/P3HT, rGO/P3HT and rGO-f-TAA/P3HT samples
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.
