Journal of Advanced Materials in Engineering (Esteghlal)

---

---

An Al-Mg-Si-Cu alloy was subjected to tensile testing, both under solutionized and ECAE-ed conditions, using strain rates of 10-4 s-1 to 10-1 s-1 at temperatures of 25 ˚C to 325 ˚C to investigate the dynamic strain aging (DSA) phenomenon in the alloy. Negative strain rate sensitivity (m) and increasing ultimate tensile stress were observed in the DSA region with increasing temperature . Regarding the activation energy of the phenomenon, it was suggested that the process is controlled by the interaction of Mg atoms with mobile dislocations at lower temperatures of DSA occurrence while at higher temperatures, the aggregation of Mg atoms and precipitates of a second phase decreases the amount of Mg atoms in the solid solution, resulting in the inverse DSA effect. Moreover, it was shown that at temperatures greater than 250 ˚C, the ratio of post-uniform to uniform elongation increases with increasing temperature or with decreasing strain rate due to the solute drag of Mg atoms in the Al matrix. Processing the alloy by ECAE transferred the negative m values to lower temperatures and decreased the tendency to DSA at higher temperatures. Calculating the mentioned ratio for the ECAE-ed specimens revealed that the post-uniform elongation dominates the uniform elongation at all examined temperatures and strain rates. Also, it was found that for ECAE-ed specimens, the ratio is not so sensitive to variations of temperature and strain rate.

---

Solid Assisted Melt Disintegration (SAMD) is a relatively new method for producing metallic powder particles in which the kinetic energy transferred from a rotating impeller to the melt via a solid medium causes melt disintegration. These droplets are then solidified and separated from the media to obtain metallic powder particles. In the present study, sodium chloride (NaCl) was used to produce Al-6wt%Si powder particles. A specified amount of NaCl was introduced into the aluminum alloy melt and the slurry was stirred following a specified time-temperature regime to disintegrate the molten alloy into droplets. This blend was quenched in water to solidify Al powder particles and to dissolve NaCl in water. The Al powder particles were then collected, washed, dried, and subjected to laser particle size (LPS) analysis and scanning electron microscopy (SEM). The effects of different time-temperature regimes on the size and morphology of the resultant Al-6wt%Si powder particles were investigated and the optimum conditions for obtaining the finest spherical particles were established. It was concluded that the finest and most spherically shaped Al powder particles could be produced by stirring the slurry at 690 °C for 5 min followed by water quenching.

---

In this research, a 3-D mathematical model is developed for simulating electromagnetic continuous removal of inclusions from molten metals. The model includes the computation of electromagnetic force field and fluid flow in the presence of electromagnetic forces. The results of flow field together with electromagnetic force field were further used for calculating the trajectory of inclusions in the molten metal. Parametric studies were performed to evaluate the effects of various parameters such as magnetic field intensity, inclusion size, and fluid velocity on inclusion removal efficiency in molten magnesium. In order to verify the mathematical model and visualize the trajectories of particles in the melt flow under electromagnetic force, a physical model was constructed. The predicted particle trajectories and separation in the physical model were compared with those obtained from experiments, which showed a relatively good agreement.

---

One of the main reasons for the blocking and sticking of the expendable layer in tundish plaster to the permanent layer and the subsequent increase in refractory consumption and associated costs is the use of low-melting phosphate binders. At high temperatures in continuous casting of steel, phosphate binders provide low-melting point melts which cause reactions between the two consuming and permanent layers, so that deskulling becomes difficult and the permanent layer is damaged. In this work, the using sulphate binders such as sulphamic acid and sulphates of aluminum, magnesium, ammonium, sodium, potassium, and calcium are studied as substitute binders. Some of the plaster properties manipulated by these different binders, namely cold crushing strength(CCS), Bulk Density (B.D), and Apparent Porosity (AP%), were measured according to ASTM. Studies by SEM and XRD showed that magnesium sulphate would be the best selection as a binder in tundish plaster. This binder provides strength at low temperatures, but dissociates to MgO and SO3 at high temperatures. SO3 evaporates and MgO is an oxide with a high melting point that does not react with the host oxide, usually MgO. No melting or reaction occurred and deskulling was easy without any damage to the permanent layer.

---

The effects of mechanochemical treatment of monoclinic zirconia in high energy planetary ball mill on its phase transformation were investigated. The mechanical treatment in ball mill reduces the grain size, increases microstrain, and causes phase transition to metastable nanostructured tetragonal and cubic phases. XRD and TEM results show considerable amounts of amorphous phase during ball milling. Surface area measurements by BET method over long milling times reveal that ZrO2 particles are agglomerated with an amorphous phase as a binder. The mechanical treatment increases the reactivity of zirconia in chlorine gas. Annealing of ball milled zirconia in the chlorine atmosphere produces oxygen vacancy in zirconia (ZrO2-x) and causes the amorphous phase to be crystallized and to change into cubic and tetragonal phases. The chlorine atmosphere increases the stability temperatures of cubic and tetragonal phases to 800°C and 1000°C, respectively. In this situation, the energy of grain boundary and oxygen vacancy play important roles in the stability of tetragonal and cubic phases.

---

In cast aluminum and its alloys, the microstructure varies under different solidification conditions, causing variations in their mechanical properties. These materials are basically produced in sand and metallic molds or through die casting, each of which is associated with a unique solidification regime with significantly different cooling rates so that the resulting microstructure strongly depends on the casting method used. In the present study, the effects of such important solidification parameters as cooling rate, solidification front velocity, and thermal gradient at the solid-liquid interface on secondary dendrite arm spacing were investigated. By a directional solidification system, the mathematical relation between cooling rate and dendrite spacing was extracted for several commercially important aluminum alloys. A neural network model was trained using the experimental values of cooling rates and secondary dendrite arm spacing. Reliable prediction of these values was made from the trained network and their corresponding diagrams were constructed. A good agreement was found between simulation and experimental values. It is concluded that the neural network constructed in this study can be employed to predict the relationship between cooling rate and dendrite arm spacing, which is difficult, if not iompossible, to accomplish experimentally.

---

In the present study phase transformation of silicon and silica during milling in different atmospheres was investigated. The silicon powder was subjected to high energy ball milling in ammonia (25%) atmosphere. The milled powder was subsequently annealed at 1200 ◦C for 1 hour. In another test a mixture of AlN and amorphous silica (micro silica) was subjected to high energy ball milling. The milled powder mixture was subsequently annealed at 1200 ◦C for 2 hours. Phase analysis of the as milled and annealed powders was performed by X-ray diffractometery (XRD). Powder morphology was also examined using a scanning electron microscope (SEM). Results showed that ball milling of silicon in ammonia formed an amorphous phase which transformed to quartz on further milling. After annealing quartz, cristobalite and another oxide phase called O phases were developed on XRD patterns. Ball milling of AlN and amorphous silica led to the transformation of amorphous silica to stishovite phase. This process was completed after annealing..

---

The initial stages of the  precipitation in a dilute Ni-Al binary alloy, Ni-11.6 at.%Al, were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electron diffraction and electron microscopy (FEG-SEM and TEM) techniques. Three samples were similarly solution treated and then cooled to room temperature under different cooling rates, 170، 25 and 0.03oCs-1. The results indicate a clearly homogenous  nucleation during rapid quenching which takes place via simultaneous ordering and phase separation. However, by decreasing the cooling rate to 25oCs-1 the nucleation mechanism changes to heterogeneous on the preferred nucleation sites. The capability of the mentioned empirical techniques for studying the initial stages of the γ′ is another subject which is studied in this article.

---

In this study, Mo-14Si-10B and Mo-57Si-10B (at%) elemental powders were separately milled using an attritor mill. Mechanically alloyed powders were agglomerated and annealed. Then, powders of Mo-Si-B as alloyed (with composites) and agglomerated (without composites) were plasma sprayed onto plain carbon steels. The samples, both coated and non-coated, were subjected to isothermal oxidation tests. Metallurgical characteristics of powders and coatings were evaluated by SEM and XRD. Plasma-sprayed Mo-Si-B coatings (with phases of MoSi2, Mo5Si3, MoB and Mo5SiB2) greatly improved the oxidation resistance of the plain steel substrates, but plasma-sprayed Mo-Si-B coatings (without any phases) did not significantly improve the oxidation rate of substrates. Also, the kinetics and composition of the oxide-scale have been found to depend on the alloy composition.

---

The addition of ZrO2 particles to the HA coating has received considerable attention because ZrO2 particles increase the bonding strength between HA coating and substrate. In this study, nanostructured hydroxyapatite (HA)/yttria stabilized zirconia (YSZ) coatings were prepared by a sol–gel method. It was found that at 950ºC, the dominant phases were HA and tetragonal (t)-zirconia in 3YSZ, cubic (c)-zirconia in 8 YSZ and t-c-Zirconia in 5YSZ phases with the small amounts of β-tricalcium phosphate (β-TCP) and CaZrO3. The crystallite size of the coating was about ~20-30 nm for tetragonal and cubic zirconia grain size and 40-80 nm for hydroxyapatite grain size. Crack-free and homogeneous HA/YSZ composite coatings were obtained with no observable defects. In vitro evaluation in 0.9% NaCl showed that Ca2+ dissolution rate of composite coatings was lower than that of pure HA coatings. The decrease in electrochemical performance of these coated samples in comparison with the uncoated type 316L St.St could be associated with chloride ion and water penetration into the coating, transport of ions through the coating, and the subsequent electrochemical reactions at the coating–metal interface.

---

In this study, forsterite nanopowder was prepared by mechanical alloying and post-heat treatment method. Bioactive properties of forsterite nanopowder were studied by immersing the powder in the SBF. Nanostructure forsterite bulk dense form was prepared by the two step sintering method. It was found that pure forsterite nanopowder with 25-60nm particle size was produced. The results of soaking of forsterite nanopowder in the SBF showed that forsterite nanopowder is bioactive. Also, forsterite dense bulk with the optimal hardness of 940 Hv and fracture toughness of 3.61 MPa.m1/2 was produced. These findings suggest that forsterite nanostructure ceramics possess good biocompatibility, bioactivity and mechanical properties and could be suitable for orthopedic and dental implant materials.

---

In this research, the reaction kinetics of TiH2 powder in contact with pure aluminum melt at various temperatures on the basis of measuring the released hydrogen gas pressure was studied. To determine the mechanism the reaction, after Solidification of samples, interface of TiH2 powder in contact with melt was studied. The results showed that PH2-time curves had three regions. In the first and second regions, the rate of reaction conforms to zero and first order, respectively. In the third region, hydrogen gas pressure remains constant and the rate of reaction becomes zero order. In the first and second regions, the main factors controlling the rate of reaction are diffusion of hydrogen atoms within titanium lattice and chemical reaction of titanium with aluminum melt, respectively. Based on the main factors controlling the rate of reaction, three temperature ranges can be considered for reaction mechanism, a) 700-750ºC, b) 750-800ºC and c) 800-1000ºC. In the temperature range (a), the reaction is mostly chemical reaction control. In the temperature range (b), the reaction is diffusion and chemical reaction control, and in the temperature range (c), the reaction is mostly diffusion control.

---

Charpy impact energy of functionally graded steels in the form of crack arrester configuration was investigated. Functionally graded steels which contain layers of ferrite, austenite, bainite and/or martensite could be produced by electroslag remelting. The results showed that notch tip position and the distances of notch with respect to the bainite and martensite layers significantly affect the impact energy of the specimens. Generally, the plastic deformation zone ahead of a crack in a functionally graded material depends on the position of the notch tip where according to the direction of gradient slope may increase or decrease. The closer the notch tips to the brittle phase, the smaller the impact energy of the specimen and vice versa. The effect of plastic zone size on impact energy of functionally graded steels was notionally investigated.

---

In the last decade, Calcium Titanate has been introduced as a bioceramic with acceptable mechanical and biological properties for orthopaedic implant applications. In this study, CaTiO3 nano-structure coating was produced by sol-gel dip-coating route for biomedical applications. Calcium nitrate and titanium isopropoxide were used as a precursor. After coating process, the specimen was subjected to rapid thermal annealing (RTA) at 800°C. The phase structure, functional groups and surface morphology of coating were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Uniform crack-free nano-structured coatings were obtained with perovskite crystal structure.

---

Fabrication of biomaterials with ability to form a bond with bone tissue for bone skeletal system repair is one of the biomaterial science aims. Bioactive glasses containing CaO-SiO2-P2O5 are among the most important groups used in biomedicine and dentistry such as bone defect repair and maxillo-facial reconstruction. The aim of this work was preparation and characterization of nano particle bioactive glass with optimum bioactivity. Bioactive glasses with three different compositions (45S, 49S and 58S) were prepared via sol- gel technique. X- ray diffraction (XRD) technique and X- ray fluorescent (XRF) method were utilized for the phase analysis and also to investigate the chemical composition of the obtained bioactive glass nanopowders. Transmision electron microscopy (TEM) and Scanning electron microscopy (SEM) were utilized to study the structure, morphology and particle size of synthesized bioactive glass nanopowders. In order to investigate the bioactivity, the prepared bioactive glasses were immersed in the simulated body fluid (SBF) solution at 37◦C for 30 days. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were utilized to recognize and confirm the apatite layer on the prepared bioactive glass nanopowders. TEM images showed that the prepared bioactive glasses had the particle sizes less than 100 nanometers. SEM, FTIR and XRD confirmed the formation of bone-like apatite layer formed on the bioactive glass nanopowders surface, confirming the bioactivity of synthesized bioactive glass nanopowders. It was concluded that the amount of apatite on the 45S bioactive glasse was greater in comparison with 49S and 58S bioactive glasses. It is notable that by optimizing the chemical composition, bioactive glass nanopowder could be used in applications such as repair of bone defects and bone replacement.

---

In this work, NiCu and CoCu alloy nanowires were prepared by electrodeposition within nuclear track-etched polycarbonate membranes with the nominal diameter of 30nm. Electrodeposition was carried out under potentiostatic control with three electrodes. In order to grow CoCu nanowires and NiCu nanowires, an electrolyte containing salts of Co and Cu, and an electrolyte containing the salts of Ni and Cu were used respectively. Then, the potentiodynamic behavior of each electrolyte was investigated by its CV curves, and the optimum potentials for the deposition of Ni, Co and Cu were selected according to these curves. A TEM microscope was used to study the structure of the nanowires. The results showed that the crystalline growth is polycrystalline and the diameter of the wires is about 80 nm. Apart from that, some nanowires were deposited under different deposition voltages. EDX analysis showed that the atomic weight of Ni and Co in all samples vanishes in the potentials between -0.5V to -0.8V which indicates that pure Cu atoms are deposited at these voltages. Deposition of Ni and Co starts at more negative voltages such as -0.9 and -0.85 V, respectively.

---

In order to increase the efficiency and working life of mettalic interconnects used in solid oxide fuel cells, protective coatings with high electrical conductivity are used. In this study, AISI 430 ferritic stainless steel was coated in a cobalt-base pack mixture by pack cementation. The effect of oxide thickness on the area specific resistance (ASR) was investigated by applying isothermal oxidation at 800 °C and non-isothermal oxidation at a temperature range of 400 – 900 ºC. Results showed that the formation of MnCo2O4 and CoCr2O4 Spinels during oxidation improved electrical conductivity. The increase of isothermal oxidation time and temperature increases the oxide thickness, and consequently the ASR increased.

---

In the present study, in-situ synthesis of carbon nanotube/hydroxyapatite nano composite powder with stable homogeneous dispersions of carbon nanotubes (CNTs) was carried out using surfactant as dispersing agent. By applying sol-gel method, dispersion in the hydroxyapatite matrix and its effects on the microstructure were investigated. The chemical and phase composition, structure and morphological and size analyses were performed using XRD, FT-IR, SEM, TEM/SAED/EDX, Raman, UV-Vis spectroscopy and differential scanning calorimetry (DSC). The influences of different dispersing agents (sodium dodecyl sulfate, SDS) as a benchmark for future dispersion experiments) and excitation wavelength are discussed and the results are compared to the commonly used UV-Visible spectroscopic analysis. The results indicated that synthesis of hydroxyapatite particles in the presence of the carbon nanotubes had the best homogenization of the carbon nanotube dispersion and faster crystallization of hydroxyapatite, and the use of SDS for dispersion carbon nanotubes at hydroxyapatite matrix rendered formation of hydroxyapatite coating on CNTs surface. The average crystallite size of heat-treated (at 600°C) samples, estimated by Scherrer,s equation, was found to be ~50-60 nm that was confirmed by TEM.

---

In this research, DTA and TGA curves of titanium hydride powder in air with the heating rates of 5, 10, 20, 25, 30ºC/min were drawn, and XRD patterns of titanium hydride powder during heating rate 10ºC/min were prepared. Results showed that hydrogen comes out of titanium hydride in air during seven stages. And, by increasing heating rate, the mechanism of hydrogen emission from titanium hydride is almost fixed. Upon computation of activation energy of these stages, it was revealed that the mechanism does change at different temperatures. According to DTA curve at 10ºC/min, at temperatures lower than 460ºC, the mechanism is controlled by internal diffusion, at temperatures between 460-650ºC, it is controlled by physicochemical process, and at temperatures higher than 650ºC, it is controlled by chemical reaction. By increasing heating rate, the mechanism is changed at higher temperatures.