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Grain Size Control in Fusion Welding and Wire-Arc Additive Manufacturing of Ferritic Stainless Steels
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Kokabi, Amir Hossein (Supervisor)
Abstract
Ferritic stainless steels, despite having a good combination of mechanical properties and corrosion properties and low price, are less used than austenitic stainless steels due to their low weldability. The main challenges of welding ferritic stainless steels are coarse grain formation in the molten area as well as grain growth in the heat affected zone. In this research, in the first phase, an attempt is made to change the shape and size of the grains in the melted zone by changing the GTAW fusion welding parameters, including welding current and welding speed. In the second phase, an attempt is made to prevent the formation of columnar grains by adding micron particles to the molten pool...
Densification and microstructural evolution during laser sintering of A356/SiC composite powders
, Article Journal of Materials Science ; Volume 46, Issue 5 , 2011 , Pages 1446-1454 ; 00222461 (ISSN) ; Godlinski, D ; Sharif University of Technology
Abstract
This article reports experimental results on laser sintering of A356 aluminum alloy and A356/SiC composite powders. Effects of scan rate, sintering atmosphere, hatch spacing, and SiC volume fraction (up to 20%), and particle size (7 and 17 μm) on the densification were studied. The phase formation and microstructural development were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Laser sintering under argon atmosphere exhibited higher densification compared to nitrogen. A faster sintering kinetics was observed as the scan rate decreased. Except at a low SiC content (5 vol%), the composite powders exhibited...
Photoconductivity and diode effect in Bi rich multiferroic BiFeO 3 thin films grown by pulsed-laser deposition
, Article Journal of Materials Science: Materials in Electronics ; Volume 22, Issue 7 , 2011 , Pages 815-820 ; 09574522 (ISSN) ; Mahdavi, S. M ; Nemati, A ; Kianinia, M ; Sharif University of Technology
2011
Abstract
Bismuth ferrite, BiFeO 3, is almost the only material that is simultaneously magnetic and a strong ferroelectric at room temperature. As a result it is the most investigated multiferroic material. In this study, bismuth ferrite thin films were deposited on silicon wafer (100) and glass by pulsed-laser deposition and their structural, optical, and electrical properties were measured. Our study indicates that Bi richness in these films can stimulate formation of oxygen vacancy in the system which in its turn leads to delocalization of carriers and a more intensified photoconductivity response. X-ray diffraction analysis revealed formation of BiFeO 3 (BFO), but it also showed formation of Bi 2O...