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Nanocrystallization of α-Fe Crystals in Fe52Cr18Mo7B16C4Nb3 Bulk Amorphous Alloy

S. Ahmadi

材料科学技术(英文)

Crystallization kinetics of Fe52Cr18Mo7B16C4Nb3 alloy was evaluated by X-ray diffraction (XRD), differential
scanning calorimetric (DSC) tests and transmission electron microscopy (TEM) observations in this research
work. In effect, crystallization and growth mechanism were investigated by using DSC tests at four different
heating rates (10, 20, 30, 40 K/min). Results showed that a two-step crystallization process occurred in
the alloy in which α-Fe and Fe3B phases were crystallized, respectively in the structure after heat treatment.
Activation energy for the first step of crystallization, i.e. α-Fe was measured to be 421 and 442 kJ/mol
according to Kissinger-Starink and Ozawa models, respectively. Further, Avrami exponent calculated from
DSC curves was 1.6 and a two-dimensional diffusion controlled growth mechanism with decreasing nucleation
rate was observed in the alloy. Moreover, it was known from the TEM observations that crystalline α-Fe phase
nucleated in the structure of the alloy in an average size of 10 nm and completely mottled morphology.

关键词: Bulk metallic glasses (BMGs)

Evaluation of the Electroslag Remelting Process in Medical Grade of 316LC Stainless Steel

S. Ahmadi

材料科学技术(英文)

This study is focused on the effects of electroslag remelting by prefused slag (CaO, Al2O3, and CaF2) on macrostructure and reduction of inclusions in the medical grade of 316LC (316LVM) stainless steel. Analysis of the obtained results indicated that for production of a uniform ingot structure during electroslag remelting, shape and depth of the molten pool should be carefully controlled. High melting rates led to deeper pool depth and interior radial solidification characteristics, while decrease in the melting rates caused more reduction of nonmetallic inclusions. Large shrinkage cavities formed during the conventional casting process in the primary ingots were found to be the cause of the fluctuation in the melting rate, pool depth and extension of equiaxed crystals zone.

关键词: Ultra clean steel , null , null , null , null

Effects of Nb Alloying on Nano-Crystallization Kinetics of Fe55-xCr18Mo7B16C4Nbx(x=0, 3) Bulk Amorphous Alloys

S. Ahmadi

材料科学技术(英文)

Crystallization kinetics of Fe55-xCr18Mo7B16C4Nbx(x= 0, 3) bulk amorphous alloys were analyzed using X-ray diffraction and differential scanning  calorimetric (DSC) tests. In practice, crystallization and growth mechanism were evaluated using DSC tests at four different heating rates (10, 20, 30, and 40 K/min) and kinetic models. Two-step crystallization behavior was observed when Fe55Cr18Mo7B16C4 and Fe52Cr18Mo7B16C4Nb3 bulk amorphous alloys were annealed, where Fe36Cr12Mo10 phase was crystallized in the first step of crystallization. Results show that Fe36Cr12Mo10 and Fe3C phases were crystallized in the structures of the alloys after further annealing process. Activation energy for the crystallization of Fe36Cr12Mo10 phase was measured to be 543 kJ/mol in Fe52Cr18Mo7B16C4Nb3 alloy and 375 kJ/mol for Fe55Cr18Mo7B16C4 alloy according to Kissinger-Starink model. Moreover, a two-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in Fe52Cr18Mo7B16C4Nb3 alloy whereas a three-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in crystallization of Fe36Cr12Mo10 phase during annealing of  Fe55Cr18Mo7B16C4 alloy. TEM (transmission electron microscopy) observations reveal that crystalline Fe36Cr12Mo10 phase nucleated in the structures of the alloys in an average size of 10 nm with completely mottled morphology.

关键词: Avrami exponent

Effects of Nb Alloying on Nano-Crystallization Kinetics of Fe55-xCr18Mo7B16C4Nbx(x=0, 3) Bulk Amorphous Alloys

S. Ahmadi

材料科学技术(英文)

Crystallization kinetics of Fe55-xCr18Mo7B16C4Nbx(x= 0, 3) bulk amorphous alloys were analyzed using X-ray diffraction and differential scanning  calorimetric (DSC) tests. In practice, crystallization and growth mechanism were evaluated using DSC tests at four different heating rates (10, 20, 30, and 40 K/min) and kinetic models. Two-step crystallization behavior was observed when Fe55Cr18Mo7B16C4 and Fe52Cr18Mo7B16C4Nb3 bulk amorphous alloys were annealed, where Fe36Cr12Mo10 phase was crystallized in the first step of crystallization. Results show that Fe36Cr12Mo10 and Fe3C phases were crystallized in the structures of the alloys after further annealing process. Activation energy for the crystallization of Fe36Cr12Mo10 phase was measured to be 543 kJ/mol in Fe52Cr18Mo7B16C4Nb3 alloy and 375 kJ/mol for Fe55Cr18Mo7B16C4 alloy according to Kissinger-Starink model. Moreover, a two-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in Fe52Cr18Mo7B16C4Nb3 alloy whereas a three-dimensional diffusion controlled growth mechanism with decreasing nucleation rate was found in crystallization of Fe36Cr12Mo10 phase during annealing of  Fe55Cr18Mo7B16C4 alloy. TEM (transmission electron microscopy) observations reveal that crystalline Fe36Cr12Mo10 phase nucleated in the structures of the alloys in an average size of 10 nm with completely mottled morphology.

关键词: Avrami exponent

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