Formation and chemistry of nanocrystalline phases formed during deformation in aluminum-rich metallic glasses

Csontos, A.; Shiflet, G. J.

doi:10.1016/s0965-9773(97)90068-4

Cited by 61 publications

(23 citation statements)

References 15 publications

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“…4,7) One type of nanocomposite that has been studied intensively is amorphous nanocomposites composed of α-Al nanocrystals finely dispersed in an amorphous matrix. 8,9) The most important characteristic of these nanocomposites is their high strength, having up to 50% higher tensile strength than the precursor amorphous alloy. 8,9) In the Al-Ni-Y system, it has been shown that the strength is controlled by the solute concentration in the amorphous matrix.…”

Section: Introductionmentioning

confidence: 99%

“…8,9) The most important characteristic of these nanocomposites is their high strength, having up to 50% higher tensile strength than the precursor amorphous alloy. 8,9) In the Al-Ni-Y system, it has been shown that the strength is controlled by the solute concentration in the amorphous matrix. 10) During the crystallisation process, which produces the dispersed α-Al nanocrystals, the average chemical composition of the amorphous matrix changes resulting in an increase in the strength.…”

Section: Introductionmentioning

confidence: 99%

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Structural Characterisation and Mechanical Properties of Nanocomposite Al-based Alloys

et al. 2002

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Nanocomposite Al-based alloys can be obtained with a combination of amorphous, crystalline and quasicrystalline phases. In order to understand the correlation between the nanostructure and the mechanical behaviour, four nanocomposite alloys with different characteristics were studied: two alloys from the Al-Fe-Cr-Ti system consisting of a spherical nanoquasicrystalline phase in an α-Al matrix; one alloy from the Al-Fe-V-Ti system consisting of a mixture of amorphous and α-Al phases; and one alloy from the Al-Mn-Cr-Cu system consisting of nanocrystalline particles embedded in an α-Al matrix. Melt-spun samples were prepared and the structure was characterised by means of X-ray diffraction and transmission electron microscopy. Differential scanning calorimetry was used to study the thermal stability and the transformation processes. Tensile tests, fractographic analysis and Vickers microhardness at room temperature were performed in order to evaluate the mechanical behaviour. A combination of solid solution, particle dispersion and grain refinement strengthening was responsible for the high strength of the alloys. The microstructure of the alloy Al 93 Fe 3 Cr 2 Ti 2 (at%) remained acceptably stable up to 703 K, due to the slow coarsening rate of the icosahedral phase.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structural Characterisation and Mechanical Properties of Nanocomposite Al-based Alloys

et al. 2002

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“…The growth is governed by diffusion control, which can be expressed by a parabolic function (R°Wüt, R = radius of the nanocrystal; D = matrix diffusivity; t = growth time). As further growth of nanocrystals proceeds, the interparticle spacing decreases and the development of a solute buildup around the nanocrystals eventually leads to the overlap of the diffusion fields, and consequently retards the further advancement of the growth front significantly [27,28]. Moreover, the interface between the Al nanocrystals and the amorphous matrix becomes irregular or dendritic as perturbations develop into the amorphous matrix which is effectively a highly undercooled liquid.…”

Section: Resultsmentioning

confidence: 99%

High Temperature AL-Nanocrystal Alloy Synthesis

Perepezko¹

2001

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Public Reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of informatioa Send comment regarding this burden estimates or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. and Aluminum-rich metallic glasses containing transition metals and rare earth elements have been found to yield finely mixed microstructures of Al nanocrystals embedded in an amorphous matrix and exhibit enhanced fracture strength with several percent strain. Upon primary crystallization of melt spun ribbons, this novel microstructure comprised of a high particle density (> 10 20 m" 3 ) of AI nanocrystals (20nm) in an amorphous matrix develops and offers exceptional strength (1500MPa) and high temperature stability (533K). Numerical modeling based upon the size distribution of the Al nanocrystals after isothermal annealing is applied to study the nucleation kinetics in the metallic glasses. In addition to the kinetic study of primary nanocrystallization, the glass transition temperature (T E ) has been assessed in Al-7at%Y-5at%Fe and Al-8at%Sm alloys. In usual calorimetric measurements, the thermal response of the primary crystallization often obscures the observation of the signal corresponding to the glass transition. As a result, T g is often assumed to be near the onset of the primary crystallization reaction (T x ). However, it has been demonstrated by modulated-temperature calorimetry that this assumption does not apply strictly to the metallic glasses under study. The thermal stabilization of the microstructure by the occurrence of diffusion field impingement allows for the observation of the glass transition of the remaining amorphous phase in the matrix by modulated DSC. The reliable assessment of the glass transition temperature provides not only a fundamental basis for the kinetics analysis, but also an important parameter in designing suitable annealing treatments that allow for the development of desired microstructures to yield optimized properties.

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“…Since atomic mobility is very sluggish, it has been suggested that a temperature rise may play a crucial role in their formation. 11 Recently, we combined nanoindentation with transmission electron microscopy (TEM) to study the effect of deformation at a low strain rate on amorphous Al 90 Fe 5 Gd 5 alloy, to rule out a temperature rise during deformation. The results indicated that mechanical deformation at or near room temperature led to the precipitation of nanocrystalline Al.…”

Section: Introductionmentioning

confidence: 99%

“…12 Mechanically induced nanocrystallization appears to be a general phenomenon, since it has been observed in Al-, Zr-, and Fe-based alloys. [1][2][3][4][5][6][7][8][9][10][11][12] However, this process is composition dependent; it may vary between otherwise similar alloys. 1,4 Mechanically induced nanocrystallization occurs exclusively at shear bands, which are the main microstructural response to plastic deformation in amorphous alloys.…”

Section: Introductionmentioning

confidence: 99%

Deformation-induced nanocrystallization: A comparison of two amorphous Al-based alloys

2005

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Using conventional and high-resolution transmission electron microscopy (HRTEM), the effects of rolling at room temperature on the microstructures of amorphous Al 90 Fe 5 Gd 5 and Al 86.8 Ni 3.7 Y 9.5 were compared. In rolled Al 90 Fe 5 Gd 5 , nanocrystallites were observed at shear bands, whereas none were observed in rolled Al 86.8 Ni 3.7 Y 9.5 . When HRTEM was combined with with Fourier transform filtering, nanoscale, low-density defects were imaged. In Al 90 Fe 5 Gd 5 , the shear bands contain few defects, which are concentrated at the boundary zone between the shear bands and undeformed region, whereas in Al 86.8 Ni 3.7 Y 9.5 , the shear bands contain a uniform distribution of defects with a density higher than the undeformed region. The preferential precipitation of nanocrystallites in rolled Al 90 Fe 5 Gd 5 is attributed to a kinetic effect due to uniformly-distributed excess free volume in the shear bands.

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Formation and chemistry of nanocrystalline phases formed during deformation in aluminum-rich metallic glasses

Cited by 61 publications

References 15 publications

Structural Characterisation and Mechanical Properties of Nanocomposite Al-based Alloys

Structural Characterisation and Mechanical Properties of Nanocomposite Al-based Alloys

High Temperature AL-Nanocrystal Alloy Synthesis

Deformation-induced nanocrystallization: A comparison of two amorphous Al-based alloys

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