مجله مواد و فناوری های پیشرفته
سال چهارم شماره 1 (بهار 1394)

Ti/Al2O3 nano-composites were fabricated using friction stir processing. In order to achieve nano-composites with different volume fraction and size of reinforcements، the rotating tool was travelled on the substrates along the grooves with various widths that were filled with 20 or 80nm sized Al2O3 powders. Nano-composites with Al2O3 volume fraction of 1. 8 to 5. 7% were resulted. Optical and transmission electron microscopy showed that the most effective factor on refining matrix grain size is the inter-reinforcements distance or in other words their volume fraction and dispersion. In addition، microstructural characterization and micro hardness and mechanical testing revealed that in addition to reinforcements، reduction of matrix grain size and interactions related to reinforcements/sub-grain features such as grain boundaries and dislocations are responsible for the enhancement of mechanical properties of the fabricated nano-composites.

In this study، titanium nitride (TiN) phase was deposited on the surface and into porous structure of three-dimensional graphene (3DG) by chemical method. This method consists of immersing of 3DG into a solution containing Ti ions and annealing under ammonia atmosphere. In this paper، effect of annealing temperature on type of synthesized phases، their morphology، and stoichiometry was investigated. For this purpose، the samples were annealed at three different temperatures of 750، 800، and 850 °C and analyzed by XRD، SEM and XPS. The results showed that increasing of annealing temperature results in increasing of lattice parameter and crystallite size، while decreasing of oxygen content inside TiN structure. Annealing at 850 °C was resulted to the most stoichiometric composition with titanium/ nitrogen atomic ratio of 1. 09.

In this research، the Ti-48Al/Ti2AlC and Ti-48Al (8Nb) /Ti2AlC composites were synthesized by means of mechanical alloying and hot pressing. Firstly، the mixture of elemental powders were subjected to mechanical alloying for 75 h and then to produce bulk samples، the milled powders were hot pressed for 1 h at 1000. Oxidation tests were carried out in air at 1000? to compare the oxidation behavior of samples. Synthesized and oxidized samples were studied by scanning electron microscopy، energy dispersive spectroscopy (EDS) and X-ray diffractometry (XRD). According to X-ray diffraction patterns، the presence of γ-TiAl and Ti2AlC phases were detected for produced samples and no phases on the base of Nb were formed. The results showed that the oxidation resistance of alloy was improved by niobium addition. The growth of rutile was suppressed by substitution Nb for Ti in TiO2 lattice. Furthermore، scale composition changed with addition of niobium that was related to the stabilization of nitride layer.

The wettability at the metal – ceramic interfaces is important in many applications، such as metal matrix composites (MMCs). The objective of the present paper is to study wetting phenomenon of aluminium base on reactios at interfacial. The effects of alloy elements such as Mg and the processing temperature on wettability were investigated theorically. The reactive wetting is governed not only by the interfacial reaction intensity،، but also by the physical and chemical properties of the resulting interface،. The calculated wetting contact angles from physical and chemical model are approximately in agreement with experimental values.

In this paper we synthesized two new organic days (dye 1 and dye 2) based on thioindigo with phenothiazine as the electron donor group. We used acrylic acid and cyanoacrylic acid as the electron acceptor anchoring group in dye 1 and dye 2 respectively. The proposed dyes were synthesized from phenothiazine as the starting material by standard reactions and characterized by different techniques such as melting point، FTIR، 1HNMR، elemental analysis and UV-Visible spectroscopy after purification. Spectrophotometric measurements of the synthesized dyes in solution and on a TiO2 substrate were carried out in order to assess changes in the status of the dyes. The wavelength of maximum absorption for dye1 and dye 2 in solution are 499 nm and 505 nm and on TiO2 films are 523 nm and 527 nm، respectively. Finally، the proposed dyes used as sensitizer in a dye solar cell structure and their photovoltaic properties investigated. The Conversion efficiency for dye 1 and dye 2 are 2. 34% and 3. 07%، respectively.

In the current study، nanocrystalline Finemet soft magnetic cores were processed and their thickness was improved by the hot pressing technique. Besides، the effect of hot pressing on the microstructure and soft magnetic properties of the amorphous precursor was compared with the conventional annealing method. First، amorphous Finemet ribbons were produced through the melt-spinning method. Thermal behavior of the amorphous Finemet ribbons and crystallization of the anocrystalline phase was studied by Differential Scanning Calorimetry. Thus، the proper crystallization temperature of the amorphous phase was specified about 550 ºC. To crystallize the nanocrystallime phase from the amorphous matrix، the produced ribbons were either annealed conventionally at 550 ºC for 30 min or hot pressed at the same temperature for 60 min، under a controlled H2/Ar atmosphere، a 30% H2، 70% Ar mixture. The formed phases were specified by X-ray diffraction، and microstructure of the formed alloy was evaluated by scanning electron microscopy. It was shown that، both methods result in the formation of α-FeSi nanocrystals embedded in an amorphous matrix. The average size of the formed α-FeSi nanocrystals was calculated by using the MAUD software، came out to be 17 and 12 nm، for annealed and hot pressed samples، respectively. Hence، hot pressing results in crystal size reduction، compared with the conventional annealing method. Moreover، this processing method can decrease the soft magnetic properties of the amorphous precursor. However، the produced cores exhibit good soft magnetic properties (Hc~ 8 Oe، σ~ 130 emu/g).

Microwave dielectric ceramics are irreplaceable components used in devices and systems utilized at microwave frequencies for example mobile and satellite communication systems. In this study the effect of the addition of different amounts of BaZrO3 on the microstructure and microwave dielectric properties of a composition based on Ba (Zn1/3Nb2/3) O3 (BZN) ceramic، i. e. (0. 9-x) Ba ([Zn0. 6Co0. 4] 1/3Nb2/3) O3–0. 1Ba (Ga1/2Ta1/2) O3–xBaZrO3 where x=0-0. 1، has been investigated. Density increased with an increase in BaZrO3 content up to x=0. 08 and then decreased. XRD analysis showed the presence of BZN phase together with a small amount of anunknown second phase for ceramics with x=0، 0. 02 and 0. 04. However، microstructural investigations through optical microscopy showed that ceramics with x=0. 06، 0. 08 and 0. 10 also contained a second phase which could not be detected by X-ray diffraction technique because a small amount of the second phase was present. No super structure peak was observed for ceramics with different BaZrO3 levels. Quality factor for the sample with x=0. 08 was 4366 GHz which was very low. The measurement of quality factor for other samples was not also possible due to their low Q values. As mentioned before? showed that all samples contained a second phase; therefore، the low values of quality factor observed for all samples could be attributed to the presence of the second phase.

In the present study، zinc selenide powder sintered by SPS method successfully completed. The effects of temperature and pressure parameters of SPS on the bulk density were investigated. To measure the density، Archimedes method، to investigate the microstructure، optical microscopy and SEM and to phase study، XRD were used. The results indicated that temperature and then pressure are the most effective and the maximum density (99. 3%) and minimum density (91. 1%) was obtained at 1100 ° C، 70 MPa and 1000 ° C، 30 MPa respectively (25 min soaking time). Also the phenomenon of plate’s crystallographic orientation was observed by XRD and was confirmed by SEM.