Browsing by Subject "Intermetallic phasis"

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    Evaluate of braze joint strength and microstructure characterize of titanium-CP with Ag-based filler alloy
    (2012) Ganjeh, E.; Sarkhosh H.; Khorsand H.; Sabet H.; Dehkordi, E.H.; Ghaffari, M.
    This research investigates the influences of brazing parameters (temperature and time) on microstructures and the mechanical properties of commercially pure (CP) titanium sheet when it is brazed with CBS34 (Ag-20Cu-22Zn-24Cd) braze filler foil. Brazing was performed in a conventional atmosphere control furnace. The brazing temperatures and holding times employed in this study were 800-870°C and 10-20min, respectively. The qualities of the brazed joints were evaluated by ultrasonic test and the microstructure and phase constitution of the bonded joints were analyzed by means of metallography, scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical properties of brazed joints were evaluated by microhardness and shear tests. The diffusion between Ti, Ag, Cu, Zn and Cd from substrate and braze alloy, developed a strong reaction between each other. A number of intermetallic phases, such as TiCu and Ti2Cu in the Ag-Zn solid solution matrix have been identified especially at 870°C - 20min. Both the brazing temperature and the holding time are critical factors for controlling the microstructure and hence the mechanical properties of the brazed joints. The optimum brazing parameters was achieved at 870°C - 20min. Based on the shear test result, all cracks propagate along the brittle intermetallic compounds like Ti2Cu in the reaction layer which typically are composed of quasi-cleavage (Ag-Zn matrix) and brittle appearance. © 2012 Elsevier Ltd.
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    Formation of B19′, B2, and amorphous phases during mechano-synthesis of nanocrystalline NiTi intermetallics
    (Elsevier BV, 2014-02) Amini, R.; Alijani, F.; Ghaffari, M.; Alizadeh, M.; Okyay, Ali Kemal
    Ni-50Ti shape memory alloy was synthesized by mechanical alloying of the elemental powders mixture under an argon gas atmosphere. The structural and microstructural properties of the alloyed powders were evaluated by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. Moreover, the Vickers microhardness of the powders was estimated at different milling times. According to the results, by milling progression, the amount of the amorphous phase increased considerably and after sufficient milling time (48h), the mechano-crystallization of the amorphous phase into the more stable crystalline phases (i.e. B2 and B19') occurred. It was found that the particles size and microhardness were significantly affected by the formation of the amorphous, B2, and B19' phases. It was also deduced that, by appropriate heating and cooling cycles, the B2 and thermally-induced B19' phases can be created. Furthermore, it was inferred that the formation of undesirable intermetallic phases (particularly NiTi2) during the heating cycle was considerably reduced by milling time evolution. © 2013 Elsevier B.V.