An Investigation toward the Nano-Crystallization of Fe55Cr18Mo7B16C4 Bulk Amorphous Alloy

Ahmadi, S.; Shahverdi, H.R.; Saremi, S.S.

doi:10.4028/www.scientific.net/AMR.383-390.3858

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HomeAdvanced Materials ResearchManufacturing Science and Technology, ICMST2011An Investigation toward the Nano-Crystallization...

An Investigation toward the Nano-Crystallization of Fe₅₅Cr₁₈Mo₇B₁₆C₄ Bulk Amorphous Alloy

Abstract:

Nano- crystallization of Fe₅₅Cr₁₈Mo₇B₁₆C₄ bulk amorphous alloy has been analyzed by X- ray diffraction, differential scanning calorimetric test, and TEM observations in this research. In practice, crystallization and growth mechanism were evaluated using DSC tests in four different heating rates (10, 20, 30, 40 K/min) and kinetic models. A two -step crystallization process was observed in the alloy in which α – Fe, Fe23B6, and Fe3C phases were crystallized in the structure after annealing process. In addition, activation energy for the first step of crystallization process (i.e. α – Fe phase) was measured to be 276 (kj/mol) and 290 (kj/mol) according to Kissinger and Ozawa models respectively. Avrami exponent calculated from DSC curves was 2 and a three -dimensional diffusion controlled mechanism with decreasing nucleation rate was observed in the alloy. Further, it is known from the TEM observations that crystalline α – Fe phase nucleated in structure of the alloy in an average size of 10 nm and completely mottled morphology.

Info:

Periodical:

Advanced Materials Research (Volumes 383-390)

Main Theme:

Manufacturing Science and Technology, ICMST2011

Edited by:

Wu Fan

Pages:

3858-3862

DOI:

https://doi.org/10.4028/www.scientific.net/AMR.383-390.3858

Citation:

S. Ahmadi et al., "An Investigation toward the Nano-Crystallization of Fe₅₅Cr₁₈Mo₇B₁₆C₄ Bulk Amorphous Alloy", Advanced Materials Research, Vols. 383-390, pp. 3858-3862, 2012

Online since:

November 2011

Authors:

S. Ahmadi, H.R. Shahverdi, S.S. Saremi

Keywords:

Avrami Exponent, Bulk Amorphous Steels (BASs), Crystallization, Kinetic Model, Morpholoy

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References

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Paper TitlePages

Crystallization of Amorphous Cu_49.7Ti_31.8Zr_11.3Ni_7.2 Alloy

Authors: Carlos Triveño Rios, R. Contieri

Abstract: Bulk metallic glasses are attractive materials for structural and functional applications when compared to crystalline materials. The Cu-based glasses exhibit particular interest due primarily to their relatively low cost and high fracture resistance. In this work the Cu_49.7Ti_31.8Zr_11.3Ni_7.2 alloy was prepared from the mixture of pure metals by arc melting and following the ingot was re-melted by centrifugal casting in wedge-section copper mould. The structure of wedge bulk sample was evaluated by a combination of X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The results show that the amorphous state is formed in the thinner region and it is maintained up to thickness of 3.5 mm in the wedge bulk-sample. The crystallization temperature was observed above 400 °C coinciding with the studies of thermal crystallization by XRD and DSC. Dynamical heating of the amorphous phase from room temperature up to 750°C showed the formation of CuTi, Cu₁₀Zr₇ e Cu₂TiZr crystalline phases.

464

Preparation of Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ Amorphous Powder and Bulk Material

Authors: Yu Wu, Xin Fu Wang, Fu Sheng Han

Abstract: Al-based amorphous materials are believed to be a promising light weight and high strength material, but the application has not yet been realized due to difficulties in fabricating bulk materials resulted from their quite weak glass forming ability. In order to overcome this difficulty, a solid state route was studied to fabricate bulk Al-based metallic glass. An amorphous Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ powder was first fabricated by mechanical alloying, and then the microstructure, glass-forming ability and crystallization behavior were characterized. The powder shows a wide supercooled liquid region (81K), and high activation energy for crystallization (312.6kJ/mol). By this powder, a bulk material was fabricated through high pressure (2GPa) sintering (673K and 723K). The microhardness of bulk sample is as high as 1215Hv, providing a solid basis for fabricating bulk materials and applications.

690

Effects of Zr Content on the Bending Property and Crystallization Behavior of Ductile Zr-Based Bulk Metallic Glasses

Authors: Neng Bin Hua, Wen Zhe Chen, Zhen Long Liao

Abstract: In this study, the effects of Zr content on the bending property, non–isothermal and isothermal crystallization kinetics of high–Zr–based BMGs were investigated. The BMGs exhibit high bending strength and their bending plasticity enhances with increasing Zr content, which is due to more free volume with high–Zr–content. During continuous heating, the crystallization phases for Zr66 and Zr70 BMGs are Zr₂Cu and Zr₂Ni phases. Zr70 alloy exhibits the highest activation energies for glass transition and crystallization because of the sluggish diffusion of large Zr atoms. Under isothermal condition, the average Avrami exponent of Zr66 alloy modeled by the JMA equation is about 2.6, implying a diffusion–controlled three dimensional crystallization growth with an increasing nucleation rate. The average Avrami exponent of 2.0 for Zr70 alloy indicates a diffusion–controlled three dimensional crystallization growth with a decreasing nucleation rate, which can be attributed to its higher activation energy for crystallization.

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