Crystallization and High Mechanical Strength of Al-Based Amorphous Alloys

Kim, Y. H.; Hiraga, Kenji; Inoue, Akihisa; Masumoto, T.; Joo, Gea‐Jae

doi:10.2320/matertrans1989.35.293

Cited by 115 publications

(59 citation statements)

References 18 publications

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“…For example, Busch et al [18] recently showed that the presence of crystalline phases increases the viscosity of a Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 metallic glass. This observation is also consistent with the results of Kim et al [33,34] who reported that the fracture strength of an amorphous Al 88 Ni 10 Y 2 was doubled when the alloy was crystallized and contained 5-12 nm-size Al particles. Thus, in the present strain rate cycle test, continuous strengthening is proposed to be a result of the continuous precipitation of nanocrystals in the amorphous matrix.…”

Section: Technical Progresssupporting

confidence: 93%

Atomic Structure and Deformation Behavior of Bulk Amorphous Alloys

Nien¹,

Hsiung²,

Choi³

2000

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Section: Technical Progresssupporting

confidence: 93%

Atomic Structure and Deformation Behavior of Bulk Amorphous Alloys

Nien¹,

Hsiung²,

Choi³

2000

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“…This method has been used to develop nanocrystalline materials in several interesting alloy categories that include the soft magnetic alloys, 2,5,6) hard magnetic alloys, 7,8) and high strength aluminum alloys. 9) In particular, while the strength of amorphous aluminum alloys has been reported to exhibit levels up to 1000 MPa, 10) alloys that undergo partial crystallization, resulting in the formation of a distribution of nano-sized crystals, have shown strengths up to 1500 MPa. 11) Since the strength of the partially crystallized alloys are found to depend on precipitate size and volume fraction, understanding and controlling the mechanisms that determine the formation of primary aluminum is of central interest.…”

Section: Introductionmentioning

confidence: 99%

Nanocrystallization Reactions in Amorphous Aluminum Alloys

et al. 2003

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Primary crystallization is the key reaction that controls the synthesis of nanostructured bulk volumes comprised of a high density (10 21 -10 23 m À3 ) of nanocrystals (7-20 nm) within an amorphous matrix. The primary crystallization kinetics in response to the annealing and the deformation of amorphous Al alloys are assessed in specific sample types and selected thermal treatments to evaluate primary nanocrystallization reactions. All amorphous Al alloy compositions are hypereutectic so that the initial phase selection of primary Al proceeds at a reduced driving free energy compared to thermodynamically favored intermetallic phases. Differential scanning calorimetry (DSC) studies on powders and melt spun ribbon (MSR) samples based upon thermal cycling and annealing below the glass transition, T g , demonstrate a strong sensitivity of the primary crystallization onset and reaction enthalpy to thermal history and the as-quenched state. Microcalorimetry investigations and careful analysis of nanocrystal size distributions for Al 92 Sm 8 MSRs following sub-T g anneals reveal a partial nanocrystallization reaction resulting from a transient, decaying nucleation rate and a limited supply of heterogeneous nucleation sites. While crystallization is generally thought of as a thermally activated process, it can also be induced in response to external forcing such as irradiation or mechanical alloying. Intense deformation of amorphous Al 88 Y 7 Fe 5 MSR, for example, yields a distribution of Al-nanocrystallites in the amorphous matrix without thermal annealing. Moreover, the results of cold-rolling experiments with melt-spun amorphous Al 85 Ni 10 Ce 5 ribbons show that the deformation process can alter the phase selection upon annealing. These results suggest that the shear process during rolling effects a local rearrangement of atoms in the amorphous matrix. The kinetics behavior highlights the important role of the as-synthesized amorphous structure, reaction pathways and transient conditions on the evolution of nanoscale microstructures during primary crystallization.

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“…Literatures 4,10,11) report the formation of nano-scale Al-particles from Al-Ni based amorphous alloys. The crystallisation kinetics of fcc-Al in Al-NiCe [10][11][12][13] and Al-Ni-Y [14][15][16][17] amorphous alloys have been intensively investigated. All these alloys contain expensive rare earth materials.…”

Section: Introductionmentioning

confidence: 99%

Crystallization Kinetics in an Amorphous Al-Ni-Mm-Fe Alloy

2003

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Differential scanning calorimeter (DSC) has been used to study the crystallization kinetics of Al 87:5 Ni 7 Mm 5 Fe 0:5 alloy. Both isochronal and isothermal DSC plots showed that the Al 87:5 Ni 7 Mm 5 Fe 0:5 alloy undergoes three stages crystallization process. The first peak corresponds to the precipitation of fcc-Al from the amorphous matrix at around 160 C. Isothermal DSC traces showed that there is a short incubation stage for the formation of nanoscale Al particles. The value of Avrami exponent suggests that the crystallization of Al crystals starts with a nucleation process for a short time and finally controlled by a growth mechanism. The second peak corresponds to the crystallization of Al 11 (La,Ce) 3 from the matrix at around 320 C with a nucleation rate, which decreases with time, and a constant growth rate. The activation energy calculated for the crystallization of Al 11 (La,Ce) 3 phase is 288 AE 5:9 kJ/mol, 324:6 AE 18 kJ/mol, 292 AE 6 kJ/mol by Kissinger, Johnson-Mehl-Avrami and Arrhenius type equations. The difference in the values of kinetic energy is mainly due to different annealing conditions. The third peak at around 340 C corresponds to the precipitation of intermetallic compounds from the remaining matrix.

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Crystallization and High Mechanical Strength of Al-Based Amorphous Alloys

Cited by 115 publications

References 18 publications

Atomic Structure and Deformation Behavior of Bulk Amorphous Alloys

Atomic Structure and Deformation Behavior of Bulk Amorphous Alloys

Nanocrystallization Reactions in Amorphous Aluminum Alloys

Crystallization Kinetics in an Amorphous Al-Ni-Mm-Fe Alloy

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