Showing 5 results for Borhani
H. R. Jafarian, E. Borhani,
Volume 10, Issue 2 (June 2013)
Abstract
In this research, variant selection of martensite transformed from ultrafine-grained (UFG) austenite fabricated by accumulative roll bonding (ARB) process and subsequent annealing was investigated with respect tomorphology of parentaustenitic phase. The results show that the original shape of austenite grain is very effective factor in determiningthe preferred variants of martensite transformed from the elongated ultrafine-grained austenite fabricated by 6-cycles via the ARB process. Annealing treatment of the austenitic samples subjected to the 6-cycle ARB processed at 873 K for 1.8 ks suppressed the variant selection by changing the morphology of austenite grains from elongated ultrafine-grains to fully-recrystallized and equiaxed fine-grains
M. Alvand, M. Naseri, E. Borhani, H. Abdollah-Pour,
Volume 15, Issue 1 (March 2018)
Abstract
Friction stir welding (FSW) is a promising technique to join aluminum alloys without having problems encountered during fusion welding processes. In the present work, the evolution of microstructure and texture in friction stir welded thin AA2024 aluminum alloy are examined by electron backscattered diffraction (EBSD) technique. The sheets with 0.8 mm thickness were successfully welded by friction stir welding at the tool rotational speeds of 500, 750, and 1000 rpm with a constant traverse speed of 160 mm/min. EBSD revealed that stir zones exhibited equiaxed recrystallized grains and the grain size increased with increasing the tool rotation rate. The fraction of high angle grain boundaries and mean misorientation angle of the boundaries in the FSW joints at 500 rpm were 63.6% and 24.96°, respectively, which were higher than those of the sample welded at 1000 rpm (53.6% and 17.37°). Crystallographic texture results indicated that the Cube {001}<100> and S {123}<634> textures in base metal gradually transformed in to Copper {112}<111> shear texture. It was found that with increasing the tool rotation rate, the intensity of Cube {001}<100>, Y {111}<112>, S {123}<634>, and Dillamore {4 4 11}<11 11 8> texture orientations increased and the intensity of Brass {011}<211> texture orientation decreased.
M. Taleblou, E. Borhani, B. Yarmand, A. Kolahi,
Volume 15, Issue 3 (September 2018)
Abstract
Thin films of SnS2 were prepared, as the absorber layer in solar cells, using an aqueous solution of SnCl4 and thiourea by spray pyrolysis technique. Effect of the Substrate temperature on the properties of these thin films was studied. Investigation via XRD showed the formation of polycrystalline SnS2 along (001) in all layers; there was no sign of other unwanted phases. With increasing of substrate temperature from 325 to 400 0C, the crystallinity of the sample was improved, after that, it deteriorated the crystallinity. Layers had granular morphology and Valley- Hills topography. UV-VIS spectra revealed that the transmittance of all layers was lower than 40% in the visible region and the band gap reduced from 2.8 to 2.55 eV with increment in temperature from 350 to 400 0C. Photoluminescence spectra of the prepared film, which was formed at 400 0C showed a dominant peak at 530 nm, caused recombination of excitons. The least electrical resistivity of the SnS2 thin film prepared at 400 0C in dark and light environment were 4.6 ×10 -3 Ωcm and 0.65×10 -3 Ωcm, respectively; which demonstrated 400 0C was the optimum temperature in point of optoelectrical properties in the SnS2 thin film.
Gholam Hussein Borhani, Saeed Reza Bakhshi, Sadegh Soltani,
Volume 18, Issue 2 (June 2021)
Abstract
In this study, Ta powder was produced from Ta scarp via chemical processes using Mg and Ca powders. At first, Tantalum scraps were converted to Tantalum oxide (Ta2O5) at 1100˚C in an oxygen atmosphere. Tantalum oxide was reduced to Tantalum powder with Mg in a vacuum environment at 950 to 1200˚C for 3 hours. The obtained Ta powders further were reacted with Ca at 950˚C for 5 hours in a vacuum atmosphere. The powders were analyzed through X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), as well as oxygen measurement. The results show that the average particles size of the produced Ta powders is about 58 nm with oxygen contents of 250 ppm.
Seyed Mohammad Mirghasemi, Ehsan Mohammad Sahrifi, Gholam Hossein Borhani, Mirtaher Seyed Beigi,
Volume 21, Issue 0 (IN PRESS 2024)
Abstract
In this study, the hot deformation and dynamic recrystallization behavior of low carbon steel containing 21 ppm boron was investigated. After homogenizing the samples at 1250 ℃ for 1-hour, hot compression tests were conducted at temperatures ranging from 850 ℃ to 1150 ℃ and strain rates from 0.01 to 10 s⁻¹, resulting in strain-stress flow curves. Following corrections, calculations and modeling were performed based on Arrhenius equations. Among them, the hyperbolic sine relationship provided the most accurate estimate and was selected as the valid model for the applied strain range. According to this model, the deformation activation energy (Q), was determined to be 293.37 KJ/mol. Additionally, critical and peak stress and strain values were obtained for each temperature and strain rate, and power relationships were established to describe their variation with respect to the Zener-Hollomon parameter (Z). Recrystallization fractions were derived by comparing the hypothetical recovery curves with the material flow curves, and the results were successfully modeled using the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The Avrami exponent was measured at approximately 2, indicating that nucleation predominantly occurred at grain boundaries. Microstructural analysis revealed that at higher Z values, recrystallization occurred along with a fraction of elongated grains, while lower Z values resulted in a greater fraction of equiaxed dynamic recrystallization (DRX) grains. The average grain sizes after compression tests at 950 ℃, 1050 ℃, and 1150 ℃ were measured as 21.9 µm, 30.4 µm, and 33.6 µm respectively at a strain rate of 0.1 s⁻¹, and 17.7 µm, 28.7 µm, and 31.3 µm at 1 s⁻¹. The overall microstructure displayed a more uniform grain size distribution with increasing deformation temperature.
