The effect of phase separation on subsequent crystallization in Al88Gd6La2Ni4

Gangopadhyay, A. K.; Croat, T. K.; Kelton, K. F.

doi:10.1016/s1359-6454(00)00196-8

Cited by 137 publications

(91 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…We see no evidence for amorphous phase separation. 20 Xing et al 21 have suggested that some high Al-content amorphous alloys are not glasses, but instead amorphous-nanocrystal composites, and that primary crystallization is grain coarsening, not a phase transition. Our observation of nanoscale Al order in the as-spun ribbon is consistent with this model, but the decrease of that order with annealing may not be.…”

mentioning

confidence: 99%

Aluminum nanoscale order in amorphous Al92Sm8 measured by fluctuation electron microscopy

Stratton

Hamann

Perepezko

et al. 2005

Applied Physics Letters

103

View full text Add to dashboard Cite

When annealed below T g , the melt-spun material exhibits a steadily decreasing nucleation rate, 4 which suggests heterogeneous nucleation. 5 The nucleation site has so far eluded structural or chemical detection, ruling out common sites like second phase interfaces or large impurity clusters. This suggests that the nucleation sites in quenched Al 92 Sm 8 may be a form of nanometer-length structure or medium-range order ͑MRO͒. Such structure is difficult to detect in amorphous materials using conventional techniques such as x-ray diffraction. 6 Here, we report fluctuation electron microscopy ͑FEM͒ ͑Refs. 7 and 8͒ measurements and simulations which find MRO associated with primary crystallization in amorphous Al 92 Sm 8 .FEM measures diffraction from nanoscale volumes using dark-field transmission electron microscopy ͑TEM͒ at a deliberately low ͑5-50 Å͒ image resolution. The magnitude of the spatial fluctuations in diffraction, measured by the normalized variance V as a function of scattering vector k, gives information about MRO at the length scale of the image resolution. 7,9 V͑k͒ depends on the three-and four-body atomic position correlation functions. 9 Peaks in V͑k͒ give information about the type of MRO from their position in k and the degree of MRO from their height. A polycrystalline sample is an extreme example of order: in a dark-field image each grain will appear brightest when it satisfies a Bragg condition in k, leading to a high peaks in V͑k͒ at the crystal reciprocal lattice k's.Samples of amorphous Al 92 Sm 8 were prepared by rapid quenching in a single wheel melt spinner at a tangential wheel speed of 55 m / s and by cold-rolling elemental foil multilayers at a 0.003 s −1 strain rate. Melt-spun ribbon samples were annealed at 130°C ͑ϽT g of 171°C͒ 3,10 under vacuum. TEM samples were prepared by electropolishing only, as ion milling can introduce spurious peaks in V͑k͒ of amorphous metals. 11 FEM was done in hollow-cone darkfield mode on a LEO 912 EFTEM at 120 kV and 16 Å resolution. Each V͑k͒ data set is the mean of measurements from at least seven areas of the sample, quoted with one standard deviation of the mean error bars.

show abstract

mentioning

confidence: 99%

Aluminum nanoscale order in amorphous Al92Sm8 measured by fluctuation electron microscopy

Stratton

Hamann

Perepezko

et al. 2005

Applied Physics Letters

103

View full text Add to dashboard Cite

show abstract

“…45) There are other catalyst generation mechanisms that have also been suggested such as the high density of internal interfaces that can be generated by a precursor phase separation in the melt. 46) This mechanism has been suggested to generate high nucleation densities in some alloys, but again the overwhelming majority of evidence that has been reported does not support such a process as a general feature for Al-base glasses.…”

Section: Heterogeneous Catalysismentioning

confidence: 99%

Nanocrystallization Reactions in Amorphous Aluminum Alloys

et al. 2003

View full text Add to dashboard Cite

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.

show abstract

“…Aluminum based bulk metallic glasses (Al-BMG) have attracted a lot of attention due to their superior mechanical properties, low density and corrosion resistance [1][2][3][4][5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%