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- 저자 : Hooman Abedi (검색결과 2 건)
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Hooman Abedi,Massoud Emamy,Jafar Rassizadehghani,Hamed Mirzadeh 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.5
The effects of cerium-based rare earth (RE) addition and hot deformation via extrusion on the microstructure and mechanicalproperties of Mg-0.5Zn-0.5Zr alloy were studied. It was found that RE addition could effectively refine the as-cast microstructureup to 2 wt% RE with a notable grain refining effect up to 1 wt% RE. High RE additions resulted in a less effectivegrain refinement and the appearance of coarse dendritic microstructure. While the as-cast strength and ductility wereenhanced by increasing RE content up to 1 wt% due to grain refinement, alloys with high RE content faced a remarkable dropin total elongation and also showed lower ultimate tensile strength (UTS) values, which was related to the interconnectedintergranular brittle intermetallics (Mg12RE) with high volume fractions. For the extruded alloy with 1 wt% RE, besidesthe fragmentation and dispersion of intermetallics, a remarkable grain refinement due to the recrystallization processes wasobserved. Accordingly, the UTS of 415 MPa, total elongation of 17% and tensile toughness of 65.9 MJ/m3 were obtained afterextrusion, which are quite superior to the corresponding values of 210 MPa, 12% and 22.1 MJ/m3 for the as-cast counterpart,respectively. Regardless of the processing condition, the grain size effect was found to be the dominant factor in determiningthe yield stress (Hall–Petch law), where the deviation of this trend due to the presence of hard Mg12REphase was discussed.
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Arman Khobzi,Mandana Adeli,Ashkan Sabour‑Bagherzadeh,Ashkan Arab,Hooman Abedi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
NiTi intermetallic compound was fabricated via two modes of the combustion synthesis process, namely, thermal explosion(TE) and self-propagating synthesis (SHS). The effect of combustion synthesis mode as well as Ni particle size on themicrostructure and microhardness of the final products was investigated. The phases in the products were determined usingXRD technique, and microstructural investigations were performed using optical as well as SEM-EDS in order to make acomparison between microstructural evolutions in each mode, other conditions being constant. The analyses showed thatthe desired B2(NiTi) was successfully formed as the primary phase in all samples, and no unreacted Ni or Ti powders werepresent. The main secondary phase was NiTi2which was invariably present in all samples; however, the percentage as wellas the morphology of the detrimental NiTi2phase was found out to be controllable by the mode of combustion as well asNi particle size. A comparison between the two modes revealed that samples produced by TE showed coarse dendritesin the microstructure; they also presented higher average microhardness values. The SHS-synthesized samples exhibitedmicrostructures similar to those observed in heat-treated and homogenized NiTi obtained from methods such as vacuum arcremelting and vacuum induction melting, and contained finely dispersed NiTi2particles. It was shown that a decrease in Niparticle size presented a grain refining effect on NiTi2in both modes.
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