مجله مواد و فناوری های پیشرفته
سال سوم شماره 3 (پاییز 1393)

Safety، economical and environmental problemsin automotive industry are leading to the development of advanced high strength steels (AHSS) with improved mechanical properties. One of the newest and most promising heat treatments for the production of AHSS is quenching and partitioning (Q&P) process. The application of this new process in various times and temperatures leads to interesting combinations of mechanical properties including high strength and good ductility. In this study،variations of mechanical properties influenced by variation of partitioning time and temperature on 1. 5142 steel was investigated. The results showed that application of Q&P process on the steel causes severe increasing of hardness. Increasing of partitioning time and also temperature leads to decreasing of hardness and increasing of elongation. With increasing of partitioning time، tensile strength initially increases and then decreases،However، increasing of partitioning temperature leads to decreasing of strength and increasing of elongation and ductility.

Ti5Si3 has gained significant attention as a high temperature structural material due to its unique combination of properties. In the present work nanostructured Ti5Si3 based alloys and composites were synthesized by using mechanically activated self-propagating high-temperature synthesis (MASHS). For this purpose، Ti، Si and Al were mixed according to nominal compositions of Ti62. 5Si37. 5، Ti62. 5Si30Al7. 5 and Ti62. 5Si22. 5Al15 and milled by high energy ball milling for 3 and 6 h. The milled powders were pressed to form pellets and then green compacts were placed in a tube furnace to synthesize. The samples were characterized by X-ray diffraction (XRD) analytical technique and scanning electron microscope (SEM) equipped with an energy-dispersive spectrum (EDS) analyzer. The results have shown، Ti5Si3 were synthesized in all samples as main phase. Ti3Al is synthesized beside the Ti5Si3 in the Ti62. 5Si22. 5Al15 composition. Crystallites size of Ti5Si3 which had been synthesized by MASHS process was measured by Williamson-hall method. Results howed the entire MASHS product have crystallites size under 100 nm. The EDS results have shown that significant amount of Si can be replaced by Al in the Ti5Si3 structure.

In this study، firstly hydroxyapatite powder using natural method and bovine bone was synthesized at temperature of 900 ° C. Then it was synthesized reproducibiliby from foam ceramic scaffolds with 0، 3، 6 and 9 wt% and 50 wt% titania hydroxyapatite wet grinding method (slurry). In order to detect the changes of phase and chemical bonds was used diffraction of X-rays and infrared light spectroscopy. Microstructure and morphology of the nano composites was examined by scanning electron microscopy. According to the results، the volume fraction of porosities were obtained about 80-85%. The compressive strength was measured 0. 14 to 1. 321 MPa. Results indicate that the best type of scaffold physical properties such as porosity and shrinkage after sintering about low percentages of titanium dioxide، the 3 and mechanical properties suitable، the high percentage of titanium dioxide is the 6 percent.

Induced thermal stresses during quenching of micro and nano-structured ZrO2 coatings from 1250oC to 20oC has been modeled using finite element method. Thermal stresses distribution of coatings has been also calculated. Results show that thermal stress in x-direction is zero at the edges of both micro and nano-structured samples. It is also concluded that shear thermal stress of nano-structured coatings is 33% lower than its value in micro ones. In addition، shear stresses in TGO layer were also calculated and the results show these stresses are 35% lower than micro ones. Modeling results validates long life time of nano-structured coatings.

In present study friction stir welding of commercially pure aluminum foams manufactured by accumulative roll-bonding process was investigated at rotational speeds of 500، 700، 900 and 1100 rpm and advancing speed of 25 mm/min. All welds were carried out bead on plate. Optical microscopy and microhardness tests were used to investigate the weldments microstructure and weld regions hardness، respectively. Aluminum foam porosity and density variation of weld region at different rotational speeds were evaluated by Archimedes’ principle. Results showed that increasing rotational speed at a constant advancing speed causes an increase in weld region density and a decrease in weld defects. Moreover، microhardness results showed that increasing the rotational speed results in an increase in weld region hardness.

The present work studies new proposed formation of Titanium Dioxide for fabricating Dye sensitized solar cells، (DSSCs). Titanium Dioxide was synthesized by hydrothermal method. Deposition of the layers performed with electrophoretic method. In addition، materials used to synthesis are inexpensive. Two structures have been synthesized in different spheres of nanometer dimensions with diameter in rang 400-500 nm and the other with nano pore in rang 20-50 nm. The efficiencies of these Cells are reliable and repeatable. Morphologies and crystal structures were studied by Scanning electron microscopy and XRD pattern respectively. The obtained power conversion efficiencies for DSSCs sensitized with these processes were 3. 8 and 6. 1 percent respectively. shear stresses in TGO layer were also calculated and the results show these stresses are 35% lower than micro ones. Modeling results validates long life time of nano-structured coatings.

Titania (titanium oxide) is one the compositions that is photo-activated under UV radiation. It is shown the adding of tungsten oxide improves this property at the artificial light. In this research، the titanium sol was made by alkoxide precursor. Sodium tungstate di-hydrate was used as tungsten oxide precursor. Sodium tungstate di-hydrate was added to titanium sol in different percentage. Dip-coating method was used by means of preparation of coatings on 316L stainless steel substrate. Crystal structure and morphology of the coatings was investigated by XRD and FE-SEM، respectively. Bound characterization of coatings was carried out by FTIR. Potentiometery method and tafel polarization tests were used to characterization of photocathodic protection properties of coatings. The XRD results showed that the entrance of tungsten oxide into titania structure decreases its crystallites size. In the other hand، the FE-SEM results indicated that the tungsten oxide addition improves the coatings morphology. The bond between the Ti-O and W-O have confirmed by FTIR investigations. In addition، it was observed that the increase of weight percentage of tungsten oxide improves the photocathodic protection properties of coatings.

In this study Nanofibers of polycaprolactam (Nylon 6) /zinc doped hydroxyapatite (HAP) were synthesized via electrospinning method. Hydroxyapatite nanoparticles containing 4 at % zinc were synthesized via chemical precipitation method. XRD and FTIR of the synthesized powders indicated that non-stoichiometric and single phase hydroxyapatite was formed. The results also showed that Zn cations have been incorporated in atomic structure of HAP. The average of particle size and crystallite were calculated 43 and 16 nm respectively. Polymeric solution was prepared throughout dissolving of 20 wt% polycaprolactam in formic acid. To synthesize the composite nonofibers، 2 wt% of synthesized ceramic powders were added to polymeric solution. Influence of voltage (15-30 kV) and flow rate (0. 1-0. 5 ml. h-1) on diameter and morphology of nanofibers were investigated. The results of SEM images showed that fibers with average diameter of 100-300 nm were formed، and also zinc doped hydroxyapatite particles were homogenously distributed between nano fibers. The results indicated that increasing of the applied voltage over 30 kV caused to romaine ticker fibers as ribbon shaped. Results also showed that the average of fiber diameter increased with decreasing the flow rate resulting in heterogeneous distribution of HAp nanoparticles. The agrigate of Zn doped HAP was formed separately when the flow rate was set to 0. 1 ml. h-1.

In this paper Fatigue behavior of various samples of Ti-6Al-4V titanium alloy were investigated using standard rotating-bending test. scanning electron microscopy (SEM) and optical microscopy (OM) were used to study the microstructure، crack propagation analysis and also to determine the chemical composition of different phases. The results revealed that the tested samples have the fatigue limit and fatigue life equal to 490 MPa and 1. 2×107 cycles، respectively. In addition، the microstructural studies showed that the nucleation and propagation of fatigue cracks occur both from surface and internal bulk of the samples. Furthermore cracks deviate from their expected direction in case of facing β phase

Aluminum and its alloys due to favorable properties such as low density and high strength to weight ratio، have found many applications in industries، particularly the automotive and aerospace. In this study، the production process of aluminum alloy 7014 using mechanical alloying in a high energy planetary mill، at a weight ratio of powder to bullet 1:20، under argon atmosphere was investigated. According to the XRD results and XRY-MAP images and also the changes in lattice parameter، with increasing milling time gradually aluminum solid solution containing zinc and magnesium elements was created and aluminum alloy 7014 after a three-hour milling established. Also، effect of milling time on crystalline size، was investigated by milling at different times (4، 6، 8، 10، 15، 20 and 25 h). finally، the crystalline size of about 11 nm was reported on 15 hours of milling. Also the Alloy hardness value increased with increasing milling time، so 130 Vickers was reported after 15 hours of the milling.