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256 results on '"Khalaj, Gholamreza"'

18. Design of explosively welded Fe-Al multilayer laminated composite pipes: A critical microscopy analysis of stand-off distance and post-weld heat treatment effects on interface properties

Author

Jandaghi, Mohammadreza, Pouraliakbar, Hesam, Moverare, Johan, Fallah, Vahid, Khalaj, Gholamreza, Jandaghi, Mohammadreza, Pouraliakbar, Hesam, Moverare, Johan, Fallah, Vahid, and Khalaj, Gholamreza

Abstract

This study examined the microstructure and mechanical properties of explosively welded (EXW) Fe-Al multilayer laminated composite pipes, specifically SS321/AA1050/AA5083, with varying stand-off distances (SD) and post-weld heat treatments (PWHT). Findings revealed that higher collision forces at higher-SD produced a wavy interface with finer grains at the AA1050/AA5083 interface. In contrast, lower-SD yielded a smooth, flat interface. At the SS321/AA1050 interface, collision energy resulted in the formation of an uneven composite reaction layer comprising multiple intermetallics. Analysis of the SS321/AA1050 interface revealed that an increase in the PWHT temperature results in diffusion toward the reaction layer, transforming the unevenly Al-rich and Fe-rich phases into a uniform Al85(Fe,Cr,Ni)15 solid solution. The increase in the fraction of this phase made the reaction layer more brittle. At the AA1050/AA5083 interface, PWHT at higher temperatures caused a significant hardness decline extending further from the interface in samples with higher-SD. On the SS321 side of the laminated composite, higher SD resulted in higher kernel average misorientation (KAM) and increased hardness. Despite a decrease in hardness after PWHT at 350 degrees C, the hardness gradient from the matrix to the interface in laminates with higher SD remained relatively unaffected, whereas the lower SD counterparts experienced a noticeable stress relief.

Published
2024
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20. Electrochemical synthesis and characterization of Cu2O nanoparticles: Effect of electrolyte composition.

Author

Ahmadi, Hamidreza, Khalaj, Gholamreza, Soleymani, Farzad, Moalem, Mohammadhossein, Pourabdollah, Majid, and Mahmoudan, Morteza

Subjects
NANOPARTICLES, PARTICLE size distribution, ELECTROLYTES, NANOPARTICLE size, CETYLTRIMETHYLAMMONIUM bromide, X-ray diffraction
Abstract

This research studied the effect of electrolyte composition NaCl, Na2SO4 and CTAB (cetyltrimethylammonium bromide, C19H42BrN) on the electrochemical synthesis of Cu2O nanoparticles. The NaCl concentration was varied in three levels of 58.5, 117 and 175.5 (g/L); the Na2SO4 concentration was changed in three levels of 24, 32 and 48 (g/L) and the CTAB concentration was adjusted in four levels of 2, 4, 6 and 15 (g/L). The current density and temperature were kept constant at 0.4 (A/cm2) and 70 °C, respectively and the cathode-anode distance was set at 2.5 cm. The morphology, composition, particle size and distribution of the samples were examined by FESEM, XRD and DLS. The results indicated that increasing the concentration of electrolyte NaCl and Na2SO4 enhanced the purity of Cu2O. The Cu2O crystals were smaller than 100 nm and formed as polycrystalline. Moreover, higher concentration of NaCl than Na2SO4 led to a better result. CTAB effectively inhibited the growth of Cu2O nanoparticles and the particle size decreased with increasing CTAB. The optimal result was achieved in the sample with 4 (g/L) CTAB and 175 (g/L) NaCl. Cu2O nanoparticles with high purity and crystal size of 27.87 nm were produced. [ABSTRACT FROM AUTHOR]

Published
2024
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36. Enhancement of low-zinc phosphate coatings with addition Ni2+and Mn2+cations: Structure, corrosion resistance and paint adhesion

Author

Heydarian, Adel, Najafi, Abolhassan, and Khalaj, Gholamreza

Abstract

Multi-cation phosphate coatings are used in various industries today to enhance the properties of the painting process. This study explored the impact of adding nickel and manganese ions to the low-zinc phosphating process on the properties of the resulting coating. The first step of the research examined the influence of the bath phosphating agents’ concentration, temperature and immersion time and pH on the phosphate coating on the steel 41Cr4 substrate. The second step explored the impact of varying concentrations of Zn, Ni and Mn cations in the phosphating bath and the third step compared the characteristics of zinc (single-cation), Zn–Ni (two-cation) and Zn–Ni–Mn (three-cation) phosphate. The surface thickness and weight per unit area of the phosphate coating, the total and free acid values, and the coating morphology and microstructure were measured; corrosion resistance tests including alkali solubility and salt spray tests were conducted. In addition, scratch, impact, hardness and bending tests of the paint layer were performed. The results indicated that introducing Ni2+and Mn2+cations into the low-zinc phosphating bath enhances the structure, corrosion resistance and paint adhesion of the phosphate coating. Scanning electron microscope images revealed that the optimal three-cation coating has a cubic and sheeted structure. Atomic force microscope analysis also demonstrated that in the tri-cation phosphate coating, compared to the zinc phosphate coating, the roughness (Ra) decreases by up to 50% and reaches 8.92 nm. The optimal three-cation coating has the highest corrosion resistance, which is attributed to the higher uniformity, lower porosity, fine crystalline structure, and high percentage of corrosion-resistant phases in the coating composition. The time to the onset of initial corrosion signs in the salt spray test, both without and with paint, increases by 50% and 225%, respectively, resulting in 11 and 180 h.

Published
2024
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