Nanocrystallization of amorphous Fe–Si–B alloys using high current density electropulsing

Lai, Zhao-Rong; Conrad, H.; Teng, Gong‐Qing; Chao, Yang

doi:10.1016/s0921-5093(00)00781-4

Cited by 59 publications

(35 citation statements)

References 12 publications

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“…[3][4][5][6] Under the repetition of electric square pulses of 10 9 A/m 2 , a decrease in T x by 150 to 170 K was observed in Fe-Si-B metallic glasses, where enhancement of atomic diffusion by the stochastic resonance was claimed to take place. [7][8][9] It is known that both passing of an electric directcurrent of 10 7 A/m 2 and the repetition of electric square pulses of 10 9 A/m 2 with a total of a few seconds for passing current cause no detectable changes in crystalline Al and Cu circuits. 10) In order to explain the observed effects of passing electric current, the concentration of electromigration force associated with a collective motion of many atoms should be taken into account.…”

Section: Introductionmentioning

confidence: 99%

Nanocrystalline Transformation and Inverse Transformation in Metallic Glasses Induced by Electropulsing

et al. 2007

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Electropulsing by means of discharge of a condenser with the decay time () of ms causes the athermal crystallization of metallic glasses when the initial current density (i d0 ) is higher than the threshold value (i d0,c ). It is indicated that the major local amorphous structures in Zr 50 Cu 50 are the amorphous structures with the short range order (SRO) similar to crystalline cubic (c) ZrCu which is the equilibrium crystalline phase above 988 K, although the mixture of crystalline Zr 2 Cu and Zr 7 Cu 10 is the equilibrium phase below 988 K. The amount of the amorphous structures with SRO similar to cZrCu may govern the thermal stability of these metallic glasses. Further in Zr 50 Cu 50 metallic glasses, the inverse transformation from the electropulsing-induced fine crystallites to the amorphous phase for subsequent electropulsing with increasing i d0 , and the Ostwald-ripening-like phenomenon under electropulsing were observed.

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Section: Introductionmentioning

confidence: 99%

Nanocrystalline Transformation and Inverse Transformation in Metallic Glasses Induced by Electropulsing

et al. 2007

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“…Recent studies reported that the crystallization of Fe-Si-B [17,18] and Fe-Si-Cu-Nb-B [19] glassy ribbons, and Zr-based BMG [20,21] can be significantly promoted by high-density pulsing current (HDPC) treatment. In the present paper, the HDPC pre-treated Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 (Vit1) BMGs have been isothermally annealed at the initial crystallization temperature for various times.…”

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Effects of crystallization fractions on mechanical properties of Zr-based metallic glass matrix composites

Qiu

Yao

Gong

2010

Sci. China Phys. Mech. Astron.

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The Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 (at.%) bulk metallic glass composites with various crystallization fractions were prepared by pretreating the bulk metallic glassy samples with pulsing current, and then by isothermal annealing at near initial crystallization temperature for different periods of time. The precipitations and crystallization fractions were studied by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), and their effects on mechanical properties of the composite were studied by microhardness, uniaxial compression test and scanning electron microscopy (SEM). The experimental results show that the primary precipitate is quasicrystalline phase and other metastable phases including Be 2 Zr, Zr 2 Cu and FCC would precipitate subsequently. In the initial crystallization process, in which the crystallization fraction increases from 0 to 8.2%, both fracture strength and plastic strain increase, with the maximum plastic strain up to 6.4%. When the crystallization fraction is larger than 8.2%, the fracture strength and the plastic strain decrease sharply. Furthermore, the alloy with low crystallization fraction is fractured by shearing, while for high crystallization fraction it is fractured by splitting and cleavage. The results show that the mechanical properties of the glassy alloy could be optimized by controlling the processing parameters. bulk metallic glass, pulsing current, crystallization fraction, plasticity, shear band PACS: 64.70.Pf, 81.40.Lm, 81.30.Mh, 61.50.KsBulk metallic glasses (BMGs) possess extraordinary properties, such as high strength and strong corrosion resistance, which has attracted much attention from scientists in the area of materials and physics [1][2][3]. Usually the strengths of BMGs come up to theoretical values, much higher than those of the crystalline alloys with the same chemical compositions [1-4]. But BMGs exhibit very limited global plasticity since they deform by shearing through the formation of shear bands that tend to form highly localized shear bands, resulting in crack formation and premature fracture [1][2][3][4][5]. Recently, however, investigations have reported that some BMGs exhibit large plastic strains in compression due to the generation of multiple shear bands [6][7][8][9][10][11]. This implies possibility to enhance the plasticity of BMGs through effectively hindering the highly localized shear along the primary shear bands and promoting the activation of shear bands. The reported results show that one way for improving the ductility of BMGs is to introduce second phases to BMGs by in-situ formation [6] or by isothermal annealing [7], which might benefit the generation of shear bands. For instance, Sun et al. [10] reported that 12% compressive plastic strain could be achieved by in-situ forming spherical crystals within the glassy matrix, while Hofmann et al. [11] reported that Zr-Ti-based bulk metallic glass matrix composites (BMGCs) display tensile plasticity of 8.6%-13.1%. However, effects of different second phases and their cryst...

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“…[22][23][24] As already mentioned, the decrease in the crystallization temperature by repetition of electric square pulses for one hour was also claimed to be associated with the stochastic enhancement of atomic diffusion. 8,9) In contrast, a distinguishing characteristics of the e-LTC due to electropulsing is the crystallization for 1 ms below 400 K 21) which may not be explained by the stochastic enhancement of atomic diffusion because rapid cool-down and enhancement of atomic diffusion for 1 ms correspond to quenching into the amorphous state. In order to clarify this issue further, electropulsing was carried out for a-Zr 60 -Cu 30 Al 10 in a liquid nitrogen (LN 2 ) bath to minimize an effect of thermal agitation for atomic diffusion.…”

Section: Introductionmentioning

confidence: 99%

“…[4][5][6][7] For FeSi-B amorphous alloys, repetition of electric square pulses of 10 9 A/m 2 with about 0.1 ms duration for one hour, a total of a few seconds for passing current, brought about a decrease in the crystallization temperature by 150 to 170 K, where enhancement of atomic diffusion by the stochastic resonance was claimed to take place. 8,9) That is, the concentration of the electromigration force through a collective motion of many atoms is claimed too. These findings stimulated theoretical works on the influence of an electric current 10,11) or an electric field 12) on the phase transformation in the light of thermodynamics.…”

Section: Introductionmentioning

confidence: 99%

Transformation to Nanocrystallites in Amorphous Alloys Induced by Resonant Electropulsing

2005

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The electropulsing-induced low temperature crystallization (e-LTC) of marginal amorphous (a-) alloys, a-Cu 50 Ti 50 and a-Pd 80 Si 20 , and a bulk amorphous alloy, a-Zr 60 Cu 30 Al 10 , was investigated by electropulsing at room temperature (RT) and in liquid nitrogen (LN 2 ). Electropulsing was made by means of discharge of a condenser which is characterized by the initial current density, i d0 , and the decay time, , where the frequency of the principal constituent Fourier component of the electropulsing is 1=2. The range of i d0 was between 10 8 and 10 10A/m 2 and that of was between 0.1 and 20 ms. For all the amorphous alloys, the e-LTC took place during single electropulsing with i d0 beyond the threshold current density, i d0,c , where i d0,c was a function of . The maximum specimen temperature during the e-LTC was, e.g., 200 K for electropulsing in LN 2 , indicating that the e-LTC is associated with an athermal process, the resonant collective motion of the relatively high density region here. The dependence of i d0,c on found for electropulsing in LN 2 showed good agreement with that observed at RT, indicating that the density fluctuation responsible for the e-LTC was that frozen at the glass transition temperature. The transmission electron microscopy observation revealed that crystallites formed by the e-LTC showed crystallographic alignment with each other, suggesting that the transformation of the relatively high density regions to a crystalline phase took place. The underlying mechanism of the e-LTC was discussed.

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Nanocrystallization of amorphous Fe–Si–B alloys using high current density electropulsing

Cited by 59 publications

References 12 publications

Nanocrystalline Transformation and Inverse Transformation in Metallic Glasses Induced by Electropulsing

Nanocrystalline Transformation and Inverse Transformation in Metallic Glasses Induced by Electropulsing

Effects of crystallization fractions on mechanical properties of Zr-based metallic glass matrix composites

Transformation to Nanocrystallites in Amorphous Alloys Induced by Resonant Electropulsing

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