نشریه فرآیندهای نوین در مهندسی مواد
پیاپی 41 (تابستان 1396)

The paper investigates influence of mechanical activation and heating rate (20°C/min and 40°C/min) on reactions occurrence in combustion synthesis process of nanostructured NiAl-Al2O3 composites by heating of Ni, NiO and Al powder mixture from 20°C to 1300°C. To study reactions occurrence, differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized. By heating the sample without mechanical activation, exothermic reaction of NiO reduction by Al and Ni-Al intermetallic phases production happened in the presence of molten Al; while mechanical activation caused occurrence of these reactions at lower temperatures and separately. By decrement in heating rate, reactions happened separately at lower temperatures. A mechanism for reactions occurrence during heating of mechanically activated sample is proposed.

In this study, the effects of cold rolling and intermediate and final annealing on the microstructure and tensile properties of Hastelloy X alloy was investigated. Three-stage cold rolling followed by intermediate annealing at 1175 ºC for 0.5 hr were performed on 10 mm thick strip at hot rolled and solution annealed condition to obtain the final thickness of 1.25 mm. The specimens prepared for tensile test within temperature range 660- 860 ºC, annealed at 1100-1200ºC for 1 hr. Microstructural investigation of the specimen’s solution annealed at temperature 1175 ºC indicated the matrix is austenite and dispersed particles are M6C carbides which are molybdenum rich precipitates. Hot tensile test results for specimens annealed at 1100, 1150 and 1200 ºC indicated a minimum ductility, at 760, 760 and 860 ºC, respectively. Tensile tests showed that the yield strength of the alloy had a weak temperature-dependence for temperature range 660- 860ºC, due to precipitation of molybdenum rich M6C carbides.

In the present study, Al-4 vol .% SiC composites were produced by mechanical alloying and the correspondence of the creep results were obtained from different methods (the advantages of lower time of test). The coefficient between impression and compression creep rate for stresses of 30 and 32.5 MPa and 35 MPa and impression stresses of three times of compression stresses (90, 97 and 111 MPa) were constant (2.5) in different microstructures. This constant coefficient showed that the condition of composite production was similar to the steady state condition of mechanical alloying process and has been proved with composite microstructure. According to the relaxation results, the different nano SiC distribution and the porosities lead to the variations in the steady state relaxation rate and the relaxation rate decrease with time was due to the work hardening mechanism. Also the high amount of coefficient showed that the effect of porosity was more than nano SiC in impression and relaxation rate increase.

in this study, magnetic powders Ba (Mg, Ti)xFe12-2xO19 and Ba (Zn, Cu)xFe12-2xO19 with x=0.5 using mechanical alloying process a high-energy mill was prepared. Continuing a sample of pure powder and two samples doped powder was produced.In order to evaluate the phase, morphological and magnetic properties by X-ray diffraction analysis (XRD), field emission scanning electron microscope (FE-SEM) and vibrating sample magnetometer (VSM) was used. X-ray patterns in temperature 1000°C confirming the composition was almost single phase barium hexaferrite. SEM represents a hexagonal plate morphology due to preferential growth of particles in the ab crystallographic directions, respectively. Magnetic studies revealed the presence of diamagnetic ions of zinc and copper in the structure of barium hexaferrite more effective than paramagnetic cations magnesium and titanium saturation magnetization and the coercivity is reduced parameters. high saturation magnetization (53emu/g) of the sample produced composition and the lowest power BaMg0.5Ti0.5Fe11O19 coercivity (50Oe) of the samples were obtained by combining BaZn0.5Cu0.5Fe11O19

In the present work, adhesion, leak rate and chemical compatibility of a series of borosilicate-based glasses, belong to ternary BaO–SiO2–B2O3 system, with AISI 430 alloys as interconnect were investigated for solid oxide fuel cell applications. Deformation behaviors of selected glasses at sealing temprature with time were characterized. Significant deformation was not appeared in the samples overtime at sealing temperature. In the next step, the leakage tests of AISI430/glass-ceramics couples were performed. Glass containing 32 % molar BaO (Ba32) had no gas leakage; a low leak rate of 10-7 to 10-8 Pam3s-1 was obtained for the glass with 37 % molar BaO (Ba37) and big leak of the system (10-3 to 10-4 Pam3s-1) for Ba42. Possible interfacial reactions between the as-received glass and cell ingredients and aging up to 100 h were also studied by scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy and X-ray dot mapping. The results showed the Ba32 and Ba37 glasses coupled with AISI430 had fine adhesion, remained stable under these conditions and were compatible with the interconnect. So, the use of these glass-ceramics will be successful in joining the ceramic electrolytes to the metallic interconnect.

In this research the (Fe,Ti)3Al-Al2O3 nanocomposite was synthesized via the reduction of Fe2O3 by Al during mechanical alloying (MA). For this purpose the Al, Ti and Fe2O3 powders were mixed with molar ratio of 3:1:1in a planetary ball mill. The structural and morphology of powder particles during different milling times were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). In order to study the thermal behavior of powder particles, Heat treatment and differential thermal analysis (DTA) were done. It was found that, the reaction of nanocomposite formation is occurred in two stages during MA. The first and second reactions were reduction of Fe2O3 by Al and (Fe,Ti)3Al formation, respectively. The crystallite size and internal strain of powder particles for Al2O3 phase after 100 h of MA, were 20 nm and 3%, respectively. Also ball milling for long time led to the reduction of Fe2O3 by Al before Al melting during DTA.

This work aimed at manufacturing and characterizing of titanium scaffolds which is coated with Akermanite for using in bone tissue engineering. In order to creating titanium scaffolds, the primary titanium powder was prepared with spacer particle elements (sodium chloride). Akermanite coating was prepared through sol-gel method and applied on the scaffold. The prepared structure was evaluated using scanning electron microscopy (SEM). Coated scaffolds were evaluated after heat treatment by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). In terms of assessing the bioactivity of titanium scaffolds, the samples were immersed in simulated body fluid (SBF). Scanning electron microscopy images of the uncoated and coated titanium scaffolds was prepared after 3,7,14 and 21 days immersing in simulated body fluid (SBF); X-Ray Diffraction analysis (XRD) confirmed the peaks of Akermanite phase in coated samples. According to the results, our study showed that coating of Akermanite on Ti scaffold can increase the bioactivity of titanium scaffolds. The final conclusion of this study confirmed that titanium scaffolds coating with Akermanite will be a suitable and useful choice in bone tissue engineering.

Recently, with decreasing energy resources, it is favorable to use new materials to increase efficiency. High heat flux coating is one of the porous coatings that are created on base plate with pressure less sintering of powders. These coatings increase surface, besides increasing bubble nucleation sites and permeability. Porosity volume, deboning strength and permeability are the most important physical property of these coatings that affected by powder size and powder morphology as well as sintering conditions. In this research, the effect of powder morphology on physical properties (porosity, deboning strength and permeability) of High Heat Flux porous coatings was investigated. Spherical, dendritic and irregular powders by using a polymeric binder were created on Cu base plate in an atmospheric control furnace (H2-N2) with specified heat treatment cycle (without any pressure). Porosimetery test was carried on porous coating samples. Results for spherical, dendritic and irregular powders were 24.5, 49.5 and 58% respectively. For mentioned samples, deboning strength was, 1.4, 0.52 and 0.82 (kN). Permeability of samples was in 3.3×10-12 to 4.8×10-12 (m2) range. Results show that maximum permeability and porosity were belonged to the irregular powder with minimum strength and spherical powder with maximum strength has minimum permeability and porosity.

In this research, a combination of Ferro- chromium powders (variable amount) and ferromolybdenum and graphite (constant amount) were coated on the st37 carbon steel substrate through Gas Tungsten Arc Welding (GTAW). In order to study properties of the layer established under the layer, scanning electron microscope (SEM), EDS element microanalysis and microhardness assessment have been used, and x-ray diffraction analysis (XRD) specified that microstructure of the samples consists of austenite and (Cr,Fe)7 , C3 carbides. In addition, it was specified that by the increase of carbon and chromium containing hard face layers, a part of carbon is spent on the formation of Cr7C3 chromium carbide, and the remainder has played a role in the formation of molybdenum carbide and chromium led to the increase of hardness. Results of the wear test specified that the highest wear resistance relates to a sample containing 13.45 chromium percentage. SEM investigation of worn surfaces in the samples specified that wear mechanism was plowing type, cutting type and cracking type.

To improve the properties of the organic coatings ceramic nanoparticles can be applied. In the present study, inorganic-organic nanocomposite coating contains SiC nnoparticles and alkyd resin was applied on the stainless still substrates. In this regard 1, 2 and 3 wt% of SiC nanoparticles were used to prepare the nanocomposite. In order to achieve a homogeneous mixture of nanoparticles and polymeric resin, magnetic stirrer and ultrasonic device were used. The coatings were deposited on the substrates by dipping technique. To study the morphology thickness and surface of the coatings, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used. The corrosion resistance of the coatings was investigated by polarization Tafel test, electrochemical impedance spectroscopy (EIS) and salt spray. Corrosion test results showed a reduction of corrosion current and an increasing in the corrosion resistance of substrate with nanocomposites coating and the sample with 3 wt% nanoparticles was selected as optimum sample by reducing current density from 9/2×10-6 to 2/2×10-9. The results of adhesion test by cross-cut method showed the reduction of coating separation from 9% to 4%. The coating thickness of sample was measured about 20 μm.