Stability and transformation to crystalline phases of amorphous ZrAlCu alloys with significant supercooled liquid region

Inoue, Akihisa; Kawase, Daisuke; Tsai, A.‐P.; Zhang, T; Masumoto, T.

doi:10.1016/0921-5093(94)90551-7

Cited by 152 publications

(48 citation statements)

References 12 publications

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“…4(d)]. Our prediction for dendritic solidification, p ≈ 3, obeys the relationship p = 1 + d (constant nucleation and growth rates in d-dimensions) confirmed experimentally [23], that follows from the steady-state traveling tip solution of the diffusion equation. In cases (ii) and (iii), p deviates from 2, as the formation of the diffusion layer is preceded by a transient period in which phase field mobility controls growth.…”

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confidence: 52%

Nucleation and Bulk Crystallization in Binary Phase Field Theory

2002

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We present a phase field theory for binary crystal nucleation. In the one-component limit, quantitative agreement is achieved with computer simulations (Lennard-Jones system) and experiments (ice-water system) using model parameters evaluated from the free energy and thickness of the interface. The critical undercoolings predicted for Cu-Ni alloys accord with the measurements, and indicate homogeneous nucleation. The Kolmogorov exponents deduced for dendritic solidification and for "soft-impingement" of particles via diffusion fields are consistent with experiment.PACS numbers: 81.10. Aj, 82.60.Nh, 64.60.Qb Understanding alloy solidification is of vast practical and theoretical importance. While the directional geometry in which the solidification front propagates from a cool surface towards the interior of a hot melt is understood fairly well, less is known of equiaxial solidification that takes place in the interior of the melt. The latter plays a central role in processes such as alloy casting, hibernation of biological tissues, hail formation, and crystallization of proteins and glasses. The least understood stage of these processes is nucleation, during which seeds of the crystalline phase appear via thermal fluctuations. Since the physical interface thickness is comparable to the typical size of critical fluctuations that are able to grow to macroscopic sizes, these fluctuations are nearly all interface. Accordingly, the diffuse interface models lead to a considerably more accurate description of nucleation than those based on a sharp interface [1,2].The phase field theory, a recent diffuse interface approach, emerged as a powerful tool for describing complex solidification patterns such as dendritic, eutectic, and peritectic growth morphologies [3]. It is of interest to extend this model to nucleation and post-nucleation growth including diffusion controlled "soft-impingement" of growing crystalline particles, expected to be responsible for the unusual transformation kinetics recently seen during the formation of nanocrystalline materials [4].In this Letter, we develop a phase field theory for crystal nucleation and growth, and apply it to current problems of unary and binary equiaxial solidification.Our starting point is the free energy functionaldeveloped along the lines described in [5,6]. Here φ and c are the phase and concentration fields, f (φ, c) = W T g(φ) + [1 − P (φ)]f S + P (φ)f L is the local free energy density, W = (1 − c)W A + cW B the free energy scale, the quartic function g(φ) = φ 2 (1 − φ) 2 /4 that emerges from density functional theory [7] ensures the doublewell form of f , while the function P (φ) = φ 3 (10 − 15φ + 6φ 2 ) switches on and off the solid and liquid contributions f S,L , taken from the ideal solution model. (A and B refer to the constituents.) For binary alloys the model contains three parameters ǫ, W A and W B that reduce to two (ǫ and W ) in the one-component limit. They can be fixed if the respective interface free energy γ, melting point T f , and interface thickn...

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confidence: 52%

Nucleation and Bulk Crystallization in Binary Phase Field Theory

2002

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“…The crystallization occurred in the supercooled liquid region by annealing for a long period of time (5.4 ks). 21) A deviation from the linear relationship was clearly observed just under the T g . The nonlinear density increase in annealed Zr 59 Cu 31 Al 10 BGAs indicates a specific glass structural change on the atomic scale because no structural difference can be seen by X-ray diffraction patterns, as shown in Fig.…”

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confidence: 95%

Drastic Increase in the Toughness of Structural Relaxed Hypoeutectic Zr59Cu31Al10 Bulk Glassy Alloy

et al. 2007

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In order to improve embrittlement phenomena by structural relaxation, Zr-enriched hypoeutectic Zr-Cu-Al bulk glassy alloys (BGAs) were examined. During annealing for structural relaxation, the density increases significantly with annealing time from 10 3 s, and apparent saturation is seen at approximately 5.4 ks. Hardness and tensile strength do not change remarkably with annealing temperature. However, the Charpy impact value increases significantly by annealing at 648 K for 5.4 ks. The tendency of distinct increase of the Charpy impact value is maximized at Zr 59 Cu 31 Al 10 in hypoeutectic Zr-Cu-Al BGAs. A drastic increase in the Charpy impact value is accompanied by an increase in nonlinear density with increasing annealing temperature. Furthermore, the mechanical properties of fully structural relaxed Zr 59 Cu 31 Al 10 BGAs are characterized by their superior shear band formation and branching ability, which can be estimated by the shear slip width before shear band opening.

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“…[33][34][35][36][37][38] Inoue et al, in the study on the Zr 65 Cu 27:5 Al 7:5 metallic glass, showed that crystallization takes place through the precipitation of a body-centered tetragonal (bct) Zr 2 Cu phase (a ¼ 0:322, and c ¼ 1:12 nm), in which Al atoms are presumably dissolved. 33) They also showed that the morphology of crystallized structures strongly depends on the annealing temperature: above T g it exhibits a dendric morphology, while below T g it shows a more smooth morphology. Based on these observations, they suggested that redistribution of constituent elements at supercooled liquid-crystalline interfaces may have taken place during the growth.…”

Section: Crystallization Behaviormentioning

confidence: 99%

Relaxation and Crystallization Behavior of the Zr50Cu40Al10 Metallic Glass

et al. 2005

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We examined relaxation and crystallization behavior of the ternary Zr 50 Cu 40 Al 10 metallic glass by using positron annihilation and transmission electron microscopy (TEM). Observed changes in positron annihilation lifetime of the alloy annealed isothermally at 673 K, which is below the glass transition temperature, correlate well with observed density changes; while coincidence Doppler broadening (CDB) spectra exhibit no significant change. These observations demonstrate that free volume decreases without a rearrangement of atoms during structural relaxation. On the other hand, CDB spectrum has exhibited considerable changes when the same alloy was annealed at 773 K. TEM observations suggested that crystallization occurs via growth of spherulites of several hundred nm in diameter, which themselves are composed of radially grown grains. Chemical analysis revealed that Cu atoms are partitioned out during the growth of the spherulites. Diffraction study indicated that the unit cell of the crystalline phase belong to an orthorhombic system with a ¼ 0:892, b ¼ 0:550, and c ¼ 1:060 nm; while remaining interspherulite regions are found to crystallize into an fcc phase with a ¼ 1:28 nm, which is probably isostructural to the 3 phase.

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Stability and transformation to crystalline phases of amorphous ZrAlCu alloys with significant supercooled liquid region

Cited by 152 publications

References 12 publications

Nucleation and Bulk Crystallization in Binary Phase Field Theory

Nucleation and Bulk Crystallization in Binary Phase Field Theory

Drastic Increase in the Toughness of Structural Relaxed Hypoeutectic Zr<SUB>59</SUB>Cu<SUB>31</SUB>Al<SUB>10</SUB> Bulk Glassy Alloy

Relaxation and Crystallization Behavior of the Zr<SUB>50</SUB>Cu<SUB>40</SUB>Al<SUB>10</SUB> Metallic Glass

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