مجله مواد و فناوری های پیشرفته
سال هشتم شماره 2 (تابستان 1398)

Barium hexaferrite compositions with different cation substitutions are known as one of the most studied materials to produce microwave absorbing composites. In the present research (Mg,Ti) substituted barium hexaferrite with chemical formula of BaFe9(Mg1.5Ti1.5)O19 have been studied. In order to investigate the effect of particle size and powder percent, micron-size (about 3μm) and nano-size (below 100nm) were synthesized via a modified sol-gel method by controlling the ingredients ratio and calcination temperature. Chemical phase formation and morphological studies were performed by XRD and SEM, respectively. In order to investigate the microwave absorption quality of the samples, ferrite/acrylic resin composites with different powder weight percents were produced. As a criterion of the microwave absorption capability, the reflection loss (RL) plots were measured at X and Ku band by the Vector Network Analyzer system and metal back method. It was found that nano-size particles have better microwave absorption efficiency and the results of the investigation may be used to enhance the design of microwave absorbing composites and their absorption performance.

In this research, susceptibility of the formation of liquation and solidification cracks during the electron beam welding of the Zhs6u superalloy was investigated. The aim of this research is obtaining of the desirable parameters of the electron beam welding for the repair process and investigation of the effect of different values of heat input on properties and microstructure of HAZ and weld area. After the pre-weld heat treatment cycle, all test samples were welded by different values of current and welding speed and by the constant value of voltage. Microstructural investigations revealed the detrimental effect of the increase in the heat input on the susceptibility of the formation of the solidification cracks in the weld region of the samples. The microstructure of the weld region was consisted of the matrix phase including and phase, eutectic phase and the carbide phase with Chinese scripts morphology. Chemical composition of these phases was similar to the chemical composition of the equivalent phases in the base material, but the morphology of the phases was completely different.

In this study, the corrosion resistance of Nickel nanocrystalline layers induced by Surface Mechanical Attrition Treatment (SMAT) in 10% NaOH was investigated. Nickel nanocrystalline layers were studied by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Optical Microscopy and roughness test. XRD patterns showed that the peaks intensities were found to decrease due to peak broadening by increasing the treatment time. However, after 60 min, the intensity of the peaks was increased. Nickel nanocrystalline layers induced by SMAT showed better corrosion resistance than that of bulk Ni in all treatment times.

In this study, the effect of strainin thermomechanical two-step aging heat treatment on mechanical properties and electrochemical corrosion resistance of Al-2024 alloy has been investigated. These results were compared with normal aging T6. For this research, samples of Al-2024 alloys were placed at ambient temperature during normal aging under different percentages of strain, and then aging treatment was completed. Four strains of 10%, 30%, 50% and 65% were applied on the samples by rolling machine. The results of tensile test with low strain rate, potentiodynamic polarization curves and optical microscopy indicated that the sample with 50% strain offered optimum combination of microstructure, mechanical strength and corrosion resistance. This is due to the fine and uniform distribution of precipitates that cause increasing of yield strength, tensile strength and corrosion resistance by 27%, 10%, and 83%, respectively, in comparison with T6 heat treated[MP2D1] . Therefore applying strain of 50%, can increase the corrosion resistance with maintaining high strength in two-step aging and thermomechanical heat treatments.

In this study, a nanocrystallite Cu-20Zn-10Al prealloyed powder was produced by mechanical alloying method from elemental powders and nanostructured samples prepared via liquid phase sintering process. The different milling times and process control agents were considered as milling parameters to determine of optimum conditions. The milled powder was investigated by means of X-ray diffraction measurements, scanning electron microscopy, particle size analysis by means of laser technique and simultaneous thermal analysis. Then the milled powder at various milling times was cold compacted at 600 MPa and sintered at different temperatures ranging from 760 to 790 °C according to liquid phase temperature measuring by diffraction thermal analysis. Microstructural characterization, compaction and densification, micro-hardness measurement and X-ray diffraction measurements were conducted from consolidated samples at different sintering temperature and milling times. The results show that a Cu-Zn-Al homogenous supersaturated solid solution with a crystallite size of 2.4 nm (by Stearic acid as PCA) was obtained after 56 h of milling time. Furthermore, the maximum densification occurred at 775 °C with a milling time of 56 h.

In this research, Li2TiO3 ceramic was sintered via heating procedures of conventional and microwave sintering. The maximum density of 3.08 g/cm3 at 1200˚C with 3 h holding time and 3.12 g/cm3 at 1300˚C without any holding time was achieved through conventional and microwave sintering, respectively. The thermal behavior was investigated using DTA-TG, phase analysis was performed by XRD technique, and microstructures were observed by FE-SEM. Also microwave measurements were performed using Network Analyser. XRD investigations showed a higher intensity of (002) peak located at 2θ=18.46˚ in microwave sintered part attributed to higher degree of cation ordering and superlattice formation. Microstructural investigations by SEM revealed the finer microstructures of microwave rather than conventionally sintered parts. The maximum microwave characteristics were measured εr= 20.29 and Q×f = 26191 GHz for parts sintered in a conventional furnace at 1200˚C and εr= 20.86 and Q×f = 25610 GHz for parts sintered in microwave at 1300˚C.

Due to ultra-high flexural flexibility, shape memory effect, high damping properties, corrosion resistance and good biocompatibility, the nitinol alloys (NiTi) are widely used in the manufacture of medical and biocompatible materials, such as stent, orthopedic implants and surgical instruments. But one of the most important problems of NiTi alloy is the release of nickel ions due to the destruction of the surface, which these ions can interfere with the enzymatic processes involved in protein synthesis and cell proliferation. The applied coating and ion implantation is one of the most important methods for improving the surface and behavior of the NiTi alloy. In this study, surface of NiTi alloy was modified by carbon plasma immersion ion implantations (CPIII). Then nanomechanical properties of coating were surveyed by atomic force microscopy (AFM) with nano-indentation, nano-scratch methods, and also corrosion behavior was investigated by polarization test in 0.5 M NaCl solution. The results indicate a completely homogeneous, uniform and free surface imperfection with a carbon ion implantation depth of about 50 nm, and decreased average surface roughness from 34to 25 nm. The ion implantation process resulted in increasing the hardness and elastic modulus of 80.7% and 21.8%, respectively, and reducing the average friction coefficient from 0.21 to 0.16, and also making dominant the shear wearing mechanism, with a 85% increase in corrosion resistance efficiency.

Here, nanostructured lead zirconate titanate (PZT) thin films were deposited on Au/SiO2 substrates through the polyol-based sol-gel process using chloride precursors and a dihydric alcohol. Propylene glycol was used as both the chelating agent and the solvent to prepare high-quality PZT thin films. Our polyol-based method exhibited several advantages: The process is cost-effective because of the low cost of the precursors, also, unlike the conventional alkoxide-based method, the prepared PZT sols were stable for several years, and the perovskite PZT phase could form at low temperature, within 450 -575°C, according to DTA/TG results. Thus, once the substrate was prepared, PZT layers were deposited by spin coating the sol, followed by ambient drying and pyrolysis at 450°C. The final PZT thin films were annealed at 575°C. X-ray diffraction (XRD) analysis confirmed crystallization of the PZT perovskite structure at 575°C in the annealed nanostructured films. Both optical and SEM images showed that PZT films are uniform and crack free. The EDS analysis confirmed that the films consist of the PZT components.