Solute partitioning in partially crystallized Al-Ni-Ce(-Cu) metallic glasses

Hara, Kazuhiro; Zhang, Y.; Tsai, An‐Pang; Inoue, Akihisa; Sakurai, Takeshi

doi:10.1016/s0956-716x(99)80035-1

Cited by 126 publications

(64 citation statements)

References 13 publications

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“…8) A nanometer scale dispersion of fcc-Al crystals in an amorphous matrix was the key feature of the microstructures. The microstructures were examined by an atom-probe field-ion microscopy 9) and the rare-earth component was demonstrated to pile up around the fcc-Al crystals due to inherently slow diffusing velocity. Kim et al 10) has ascribed the hardening origin to the presence of small crystals that are defect free and capable of having a greater resistance to deformation than the amorphous matrix.…”

Section: Introductionmentioning

confidence: 99%

Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al89La6Ni5 Metallic Glass Matrix Composites

et al. 2007

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A spray-formed Al 89 La 6 Ni 5 metallic glass matrix composite plate was obtained in thickness of 1 mm and diameter of 200 mm, comprising over 64% primary crystals (e.g. Al 11 La 3 ) uniformly dispersed in the glass matrix. The microstructure can not be achieved by annealing corresponding amorphous precursor. The crystals existing in the glass matrix were found to increase the hardness of the composite. Through nanoindentation test, the hardness and modulus of the composite at ambient temperature were found superior than its amorphous ribbon counterpart. The hardness of the composite was estimated with the rule of mixture from the constituents to be 4.4 GPa, which agreed well with the nanoindentation results. From loss modulus measurement and TMA test at elevated temperatures, a weak T g signal in the range of 213-240 C was revealed in the as-spray-formed composite. Furthermore, the dimension shrinkage of the composite was only 0.5% during the TMA test, which is much smaller than that of amorphous ribbon counterpart by up to 20%. The enhanced hardness by constituent second phases and the dimension stability of the composite are associated with their inherent microstructure, the primary crystals in particular.

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Section: Introductionmentioning

confidence: 99%

Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al89La6Ni5 Metallic Glass Matrix Composites

et al. 2007

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“…The reason for such a high strength of the nanoscale Al phase has been thought to be due to the following two factors, i.e., (1) defect-free perfect crystal structure, and (2) highly defected crystal structure. The former mechanism was proposed about 20 years ago 26 . However, recent HRTEM data shown in Figure 7 indicates the existence of an ultra-high density of dislocations inside fcc-Al phase and the density reaches as high as the order of 10 24 ~ m -3 [27] .…”

Section: Al-based Nanocrystalline Alloysmentioning

confidence: 99%

Development and Applications of Highly Functional Al-based Materials by Use of Metastable Phases

et al. 2015

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In recent years, there has been a strong demand of developing advanced structural materials with functional properties such as high specific strength, high elevated temperature specific strength, high fatigue specific strength, low corrosion loss and low wear loss. This is because the practical uses of these functional structure materials are expected to cause the saving of material amount, reductions of material cost and energy during material production as well as the saving of consuming energy during practical uses. Besides, the light-weight materials with high corrosion resistance and high wear resistance are effective for the increase of endurance limit and the lightening of final products. Thus, the development of novel Al-based alloys having simultaneously the above-described functional properties is particularly important nowadays.As strengthening mechanisms for Al-based alloys, the following seven mechanisms are generally known 1 : solid solution, grain size refinement, work hardening, age hardening, precipitation, dispersion and defect-induced solute segregation. We have also noticed that the use of rapid quenching enables highly supercooled liquid solidification in conjunction with a high nucleation rate and low growth rate. By utilizing the high nucleation rate and low growth rate phenomenon, we have synthesized various kinds of metastable phases which change from nanocrystalline base structure to bulk glassy base structure through an amorphous base structure with increasing quenching effect (cooling rate). It is also known that the quenching effect is dominated by cooling rate from melt resulting from rapid solidification processes as well as by supercooling capacity of alloy liquid depending on alloy component and composition.When we focus on the strengthening caused by metastable phases, the effect is due to the combination of solid solution + ultra-high density of defects for amorphous phase and dispersion + grain size refinement + segregation for nanocrystalline phase. The amorphous plus nanocrystalline mixed phase alloys are expected to have simultaneously almost all the strengthening mechanisms. By utilizing the combined strengthening mechanisms of these metastable phases, we have tried to prepare novel Al-based alloys with the high tensile strength exceeding 1500 MPa at room temperature, high elevated temperature strength above 500 MPa at 573 K, high rotating beam fatigue strength above 400 MPa at 10 7 cycles, high elevated temperature fatigue strength above 100 MPa at 673 K after 10 6 cycles and high corrosion resistance below 20 mm/year in 0.25 M NaOH aqueous solution at 293 K. In addition, these Al-based alloys have been requested to exhibit a low wear loss, low coefficient of thermal expansion and low material density etc. This paper presents the review of the development achievements of metastable Al-based alloys obtained in our group on the basis of the above-described backgrounds and objectives. This paper reviews the features of alloy components, structure and mechanical properties, p...

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“…However, it has been established by APFIM measurements that the large rare earth atom solutes do not distribute uniformly within the amorphous matrix, but tend to pile up at the interface between the nanocrystal and the matrix. 29,38) The non-uniform distribution will inhibit further transformation of existing nanocrystals, restrict the volume that is available for further nucleation and will also lead to a reduction in nucleation rate. Therefore, at a high nucleation rate, the nucleation process for Al nanocrystals takes place under conditions that tend to be transient in nature.…”

Section: Phase Selection During Primary Crystallizationmentioning

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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Solute partitioning in partially crystallized Al-Ni-Ce(-Cu) metallic glasses

Cited by 126 publications

References 13 publications

Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al<SUB>89</SUB>La<SUB>6</SUB>Ni<SUB>5</SUB> Metallic Glass Matrix Composites

Thermal Stability and Mechanical Properties of Spray-Formed and Melt-Spun Al<SUB>89</SUB>La<SUB>6</SUB>Ni<SUB>5</SUB> Metallic Glass Matrix Composites

Development and Applications of Highly Functional Al-based Materials by Use of Metastable Phases

Nanocrystallization Reactions in Amorphous Aluminum Alloys

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