فهرست مطالب

Advanced Materials and Processing - Volume:8 Issue: 2, Spring 2020

Journal of advanced materials and processing
Volume:8 Issue: 2, Spring 2020

  • تاریخ انتشار: 1400/03/31
  • تعداد عناوین: 6
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  • Pages 1-2
  • Imed Boukhris * Pages 3-10
    In insulating materials, the accumulation of space charge is regarded as the main source of dielectric breakdown, which depends on their electrical lifetime. Within this work, a bipolar transport charge model is presented to study the phenomenon of electrical breakdown in low density polyethylene used for electrical insulation. Therefore, the sample thickness effect is observed on the charge dynamic and particular interest in the external current density is developed in the dielectric breakdown of the insulator, as a first witness. Distribution of the electric field is displayed by model results besides the net charge density in the insulator before and during the breakdown phenomenon. In fact, these distributions are highly related to the development of the external current density which reflects the breakdown phenomenon. In fact, these distributions are highly related to the development of the external current density which reflects the breakdown phenomenon. In fact, these distributions are highly related to the development of the external current density which reflects the breakdown phenomenon.
    Keywords: Space charge, Breakdown, Electrical lifetime
  • Masoud Arastouei *, Mohammad Khodaei, Seyed Mohmaad Atyabi, Milad Jafari Nodoushan Pages 11-19
    Bone tissue engineering serves as a solution to repair and rebuild the damaged bone. In this study, first, the akermanite nanoparticles were synthesized by the sol-gel method; then the polylactic acid (PLA) scaffold was made using the fused deposition modelling (FDM), and the akermanite nanoparticle booster was used to improve its properties. The image of the electron microscopy (TEM) from akermanite particles showed that the size of these particles was 100 nm. The microstructure and phases of the scaffold was examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results of the field emission electron microscopy (FESEM) and energy dispersive spectroscopy (EDS, map) showed that the nanoparticles had a uniform distribution in the polymer matrix. The results of the compression test also revealed that the addition of akermanite nanoparticles improved the strength of the polymer scaffold. The bioactivity test was performed by immersing the scaffolds in the simulate body fluid (SBF) and then was examined using (SEM). Formation of the hydroxyapatite crystals on the surface of the scaffold containing akermanite nanoparticles, showing that the addition of akermanite particles improved the bioactivity and mechanical properties of the scaffold; therefore, this scaffold could be a good choice for use in bone tissue engineering.
    Keywords: Akermanite, Polylactic Acid, Fused deposition modelling, scaffold
  • Mohammad Tabeahmadi, Reza Dehmolaei *, Sayed Reza Alavi Zaree Pages 20-31
    In this study, optimization of advanced square wave alternative current GTAW(ASW-AC-GTAW) parameters were conducted to improve localized corrosion resistance of AA6082-T651 aluminum alloy welds. To this objective, positive half cycle current(PHC), negative half cycle current(NHC), frequency(F) and positive half cycle current percentage(PHC%) were selected as main welding parameters and altered at three levels according to Taguchi method and L_9 (3^4) orthogonal array. To study the localized corrosion resistance of weld metals; potentiodynamic polarization test was performed on all samples and corresponding "Δ" "E" _"pit" (E_pit-E_corr )(mV) were measured and considered as evaluation criterion. Implementation of variance analysis(ANOVA) on measured data and "S" ⁄"N" (Signal-to-Noise) ratios indicated that the optimum levels of PHC, NHC, F, and PHC% were 300A, 190A, 2Hz, 40%, respectively. According to ANOVA of "S" ⁄"N" ratios, contribution of PHC, NHC, F, and PHC% to the results were 35.05%, 25.98%, 23.57%, and 15.27%, consecutively. Interval domain for average "Δ" "E" _"pit" calculated with 95% confidence level to be (379.4 , 386.54) (mV). confirmation sample was welded under optimum condition. The values of "Δ" "E" _"pit" of optimum sample were 381.13 and 385.47 mV. Both of this measurement fallen in the Interval domain. Therefore, the experimental results were in excellent agreement with analytical predictions. The regression model for predicting ΔE_pit values was obtained using multivariate nonlinear regression.
    Keywords: AA6082-T651 alloy, localized corrosion, Taguchi Method, Analysis of variance(ANOVA), regression method
  • Morteza Hadi *, Iman Ebrahimzadeh, Omid Bayat Pages 33-42

    Age hardening behavior and the related changes were studied to elucidate the hardening mechanism of an Ag–Cu–Pd alloy by Differential Scanning Calorimetry (DSC), hardness test, X-ray diffraction (XRD), scanning electron microscopic (SEM) observations and an energy dispersive spectrometer (EDS). The results showed that the hardness of the alloy was raised to 90% and 68% of its solution state value by isothermal aging at 300 ◦C and 400 ◦C, respectively. However, aging at 500 ◦C led to a decrease in the hardness of the alloy. Moreover, while age hardening at 300 ◦C occurred because of coherency strains between the (111) plane of Ag-rich and the (111) plane of Cu3Pd phases, the mechanism of aging at 400 ◦C was the formation of Cu3Pd superlattice with the L12-type crystal structure. In contrast, reduction of the Cu3Pd phase from the microstructure and formation of the Cu solid solution decreased hardness during aging at 500oC.

    Keywords: : Ag-Cu-Pd alloys, Age-hardening, Scanning Electron Microscopy, X-ray diffraction
  • Mohammad Mahdavi *, Mehdi Emamalizadeh, Arash Shokrolahi Pages 43-55
    In the present research, the ZrB2 nano-powders are synthesized at low-temperature through heating a mixture of ZrCl4, B2O3, and Na metal in a molar ratio of 1:2:4 at 650 to 950 ºC under argon atmosphere. The effect of various parameters involved in phase transformation and morphology of the ZrB2 nano-powders are investigated. Also, the influence of the reactant's stoichiometry and different factors bearing upon the granulation of ZrB2 particles was examined systematically. In particular, the effects of NaCl salt addition, as well as effective thermodynamic parameters in the above synthesis process, were studied. The morphology of samples is characterized with the help of scanning and transmission electron microscopy. The XRD results show the presence of ZrB2 single phase in the product. The obtained images indicate that the synthesized powders have a crystallite nano-metric size ranging from 11 to 26 nm. The TEM images and statistical size distribution also reveal the presence of narrow size distribution of ZrB2 nano-particles. Also, various enhancement parameters like temperature, reaction time, and diluent component on the quality of the synthesized ZrB2 nano-powders were explored and reported.
    Keywords: Ultrahigh-temperature ceramics, Zirconium Diboride, Low-temperature synthesis