Showing 6 results for Momeni
H. Momeni, H. Razavi, S. G. Shabestari,
Volume 8, Issue 2 (spring 2011 2011)
Abstract
Abstract: The supersolidus liquid phase sintering characteristics of commercial 2024 pre-alloyed powder was studied at different sintering conditions. Pre-alloyed 2024 aluminum alloy powder was produced via air atomizing process with particle size of less than 100 µm. The solidus and liquidus temperatures of the produced alloy were determined using differential thermal analysis (DTA). The sintering process was performed at various temperatures ranging from the solidus to liquidus temperatures in dry N2 gas atmosphere for 30 min in a tube furnace. The maximum density of the 2024 aluminum alloy was obtained at 610ºC which yields parts with a relative density of 98.8% of the theoretical density. The density of the sintered samples increased to the maximum 99.3% of the theoretical density with the addition of 0.1 wt. %Sn powder to the 2024 pre-alloyed powder. The maximum density was obtained at 15% liquid volume fraction for both powder mixtures.
M. Momeni, M. Esfandiari, M. H. Moayed,
Volume 9, Issue 4 (December 2012)
Abstract
Several surface modification techniques such as ion implantation, surface laser melting, have been employed to improve pitting corrosion resistance of stainless steel. Electropolishing is a technique in which the surface roughness is eliminated through a selective electrochemical dissolution. The effect of electropolishing on pitting corrosion of 304 stainless steel (SS) was investigated employing polarization technique in conjunction with the scanning electron microcopy examination. Electropolishing process was carried out on wire of 2 mm diameter in 70% phosphoric acid solution at room temperature for 30 min. To elucidate the effect of roughness elimination on pitting corrosion, investigation was carried out on as-received specimen with surface finishing of 60 SiC grit and electropolished specimen in 0.5M NaCl solution at room temperature. A significant decrease on passive current density and also shift of pitting potential towards noble value was recorded on electropolished specimen revealing a pronounce effect of this technique on surface modification. Further investigation was carried out by employing slow ramp anodic potentiodynamic polarization on as received and electropolished specimen. Plot of metastable pitting current transient revealed the reduction on the number and magnitude of metastable pitting transients prior to occurrence of stable pitting on electropolished specimen. EDX analysis of the surface area of as received and electropolished specimens showed modification in surface roughness during electropolishing was the main reason of pitting corrosion improvement. Scanning microscopy investigation of polarized specimens beyond the pitting potential revealed that in as-receives specimen pits were nucleated in at and in the vicinity of surface scratches that was created during surface abrading
H. Momeni, S. Shabestari, S.h. Razavi,
Volume 17, Issue 4 (December 2020)
Abstract
In this research, densification and shape distortion of the Al-Cu-Mg (Al2024) pre-alloyed powder compact in the supersolidus liquid phase sintering process (SLPS) were investigated. The effect of Sn on the sintering process was also studied. The powders were compacted at pressures ranging from 100 to 500 MPa in a cylindrical die. The sintering process was performed in a dry N2 atmosphere at various temperatures (580-620 ºC) for 30 min at a heating rate of 10 ºCmin-1. Results showed that the onset of densification process was observed at 600ºC and onset of distortion was occurred at 610ºC. Addition of 0.1 wt. %Sn to the alloy has increased the distortion of the samples produced from Al-Cu-Mg pre-alloyed powder, but their densification has been improved. The compact pressure of 200MPa caused the complete densification at the optimum sintering temperature and at the compact pressures greater than 200MPa; the sintered density was independent of green density.
Sasan Ranjbar Motlagh, Hosein Momeni, Naser Ehsani,
Volume 18, Issue 1 (March 2021)
Abstract
In this study, the effect of annealing treatment on microstructure and mechanical properties of Nb-10Hf-1Ti wt.% produced by Spark Plasma Sintering (SPS) was investigated. Scanning electron microscope (SEM), optical microscopy, X-ray diffraction analysis, hardness, and uniaxial tension test were used. Annealing treatment was carried out in a vacuum of 10-3 Pa at 1150 °C for 1, 3, 5, and 7 hours and in an argon atmosphere at 1350 °C for 5 hours. Internal oxidation and subsequent hafnium oxide formation causes the hardening of the C103 alloy and drastically increases hardness and tensile strength. Although HfO2 particles formed in the grain boundary cause brittleness and cleavage fracture of samples. Volume fraction, particle size, and mean interparticle spacing of oxides significantly change by annealing and subsequently the mechanical properties are affected. The SPSed sample at 1500 ℃ is softened by annealing at 1150 ℃ for 5 hours and its hardness and yield strength are reduced from 303 Hv to 230 Hv and 538 MPa to 490 MPa respectively. While annealing at 1350 ℃for 5 hours increases hardness and yield strength increases to 343 Hv and 581 MPa.
Sara Ahmadi, Reza Momeni,
Volume 20, Issue 4 (December 2023)
Abstract
The polymer modified cementitious tile adhesives are very significant in construction sector. In order to considerably improve the bond qualities of the tile adhesive in polymer modified mortars, the proportions of constituent ingredients should be carefully selected. Consequently, to design high performance tile adhesives, interactions between all the components, such as the adhesion mechanisms between the polymers film and the substrate and the effect of various additives should be recognized. The effect of vinyl acetate ethylene (EVA), high alumina cement (HAC), and additives such as calcium formate and polycarboxylate on the adhesion qualities of ceramic tile adhesive was explored in this study. The findings indicated that these ingredients had an impact on the mortars' adhesive properties, and it is necessary to find their optimal amounts in order to achieve the maximum adherence. The results showed that the tensile strength of mortar was increased with increasing the polymer amounts. A microstructural analysis revealed that the polymer was distributed homogenously throughout the mortar. The optimum amount of the used high alumina cement was determined 3 wt.%. Additionally, increasing the amount of accelerator and super plasticizer increased the tensile strength of ceramic tile adhesive by approximately 20-30%.
Hossein Momeni, Sasan Ranjbar Motlagh,
Volume 21, Issue 3 (September 2024)
Abstract
The present work deals with the hot deformation behavior of commercial Nb alloy C-103 and its microstructure evolution during uniaxial compression tests in the temperature range of 700-1100 °C and the strain rate range of 0.001-0.4 s-1. Strain rate sensitivity, calculated from the compression tests data, was almost constant and showed a negative value in the temperature range of 700-900 °C but increased significantly beyond 900 °C. Dynamic strain aging was found to have a predominant effect up to 900 °C, beyond which dynamic recovery and oxidation influenced the compressive properties. The microstructure of the deformed samples showed indications of dynamic recrystallization within the high strain rate sensitivity domain and features of flow instability in the regime of low strain rate sensitivity. The 950–1000 °C temperature range and strain rate range of 0.001-0.1 s-1 were suggested as suitable hot deformation conditions. The constitutive equation was established to describe the alloy's flow behavior, and the average activation energy for plastic flow was calculated to be 267 kJ/mol.
