Large-sized CuZr-based Bulk Metallic Glass Composite with Enhanced Mechanical Properties

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Ding Junfeng, Liu Zengqian, Wang Hui, Zhang Tao. Large-sized CuZr-based Bulk Metallic Glass Composite with Enhanced Mechanical Properties. Journal of Materials Science & Technology, 2014, 30(6): 590-594 Copy to clipboard

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Large-sized CuZr-based Bulk Metallic Glass Composite with Enhanced Mechanical Properties

Ding Junfeng¹, Liu Zengqian^1,², Wang Hui¹, Zhang Tao^1,^*

1. Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, China

2. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Corresponding author. Prof., Ph.D.; Tel.: +86 10 82314869

Abstract

A large-sized CuZr-based bulk metallic glass (BMG) composite with enhanced mechanical properties is prepared successfully. With the addition of Ta to CuZr-based alloys, the critical composite size changes and the microstructure diversifies. The composite with 0.5 at.% Ta addition has the largest critical size with the microstructure of single CuZr(B2) phase uniformly dispersing in amorphous matrix. This composite exhibits good mechanical properties, i.e., large compressive plasticity and work-hardening ability, which should be attributed to the uniformly distributed CuZr(B2) phase. The increased critical size of CuZr-based BMG composite can be explained by the fact that proper Ta addition can suppress the precipitation of crystalline phases other than B2 CuZr phase during solidification. This study may be helpful for the fabrication of large-sized BMG composites with excellent mechanical properties.

Keyword: CuZr-based BMG composite; Microstructure; Mechanical properties

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1. Introduction

Bulk metallic glasses (BMGs) have attracted great attention owing to their unique properties compared with their crystalline counterparts, such as high strength, high hardness, large elastic strain limit and good corrosion resistance^{[1], [2], [3], [4] and [5]}. However, the monolithic BMGs usually exhibit typical room-temperature brittleness and strain-softening phenomenon^{[6], [7] and [8]}, which have strictly limited their applications as structural materials. Recently, BMG composites (BMGCs), especially those with in-situ crystalline phases, have been prepared to circumvent some of these weaknesses of monolithic BMGs and several classes of BMGCs with excellent properties have been developed successfully^{[9], [10], [11], [12], [13], [14], [15], [16] and [17]}. The plasticizing mechanism involved is that the ductile crystalline phases embedded in the glassy matrix can hinder the propagation of shear bands and lead to their multiplication effectively during deformation. Among them, the meaningful combination of pronounced compressive plasticity and macroscopic work-hardening ability was obtained by the introduction of CuZr(B2) phase into the amorphous matrix in the CuZr-based BMGCs. And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]}.

In recent years, CuZr-based BMGCs have been studied widely due to their enhanced tensile properties and work-hardening ability^{[21] and [25]}. Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]}. But the limited cast dimension of BMGCs is still a stumbling block and severely restricts their applications. Although previous reports about pinpointing the formation of BMGCs may provide some meaningful guidance ^[27], the dimension of composite samples, containing CuZr(B2) as the single precipitated crystalline phase in the amorphous matrix, is still in millimeter scale. Hence, an increase in the dimension of CuZr-based BMGCs with excellent mechanical performance is required to promote their potential engineering applications.

In this paper, we present the effect of Ta addition in Cu–Zr–Al–Sn quaternary system on improving the critical size of BMGCs while maintaining CuZr(B2) as the single embedded crystalline phase simultaneously. Centimeter-scale CuZr-based BMGCs with superior compressive property were synthesized successfully. This is expected to shed light on the composition design and preparation of novel large-scale BMGCs with excellent mechanical properties and facilitate the structural applications of the BMGCs.

2. Experimental

Alloy ingots with nominal compositions of Cu_{46.15-0.5 x}Zr_{45.35-0.5 x}Al_7.5Sn₁Ta_x (0 ≤ x ≤ 0.9, at.%) were prepared by arc-melting mixtures of constituent elements (purity > 99.9%) under a Ti-gettered high-purity argon atmosphere. To ensure the compositional homogeneity, pre-alloys of elements Ta and Zr, which have relatively high melting points and large solubility at high temperature, were prepared firstly. The mixtures of pre-alloys and the other pure metals were then remelted for five times. Ribbons and rod samples were prepared through melt spinning and tilt casting, respectively. And the induction melting method was used in both processes to melt the alloy pieces.

The phase structure of the as-cast rods was determined by X-ray diffraction (XRD: Bruker AXS D8) with a Cu Kα radiation ( λ = 0.1541 nm). Microstructure of the samples was analyzed by electron probe microanalysis (EPMA: JEOL JXA 8100) using the BSE mode. Volume fraction and size distribution of crystalline phases in the composites were estimated according to the images of the cross-section surfaces^{[21] and [25]}. Compositions of the phases were determined under an energy dispersive spectrometer (EDS). Detailed structure was examined by transmission electron microscopy (TEM), using a JEM 2100F instrument equipped with a field emission gun. The samples for this study were mechanically polished to ∼50 μm thick and then electropolished using a mixed solution of HNO₃ and CH₃OH with a volume ratio of 1:3. Thermal properties, mainly about the behaviors of glass transition and crystallization of glassy ribbons were measured with a differential scanning calorimeter (DSC: NETZSCH 404 C) at a heating rate of 0.33 K/s. Melting and cooling processes of the master alloys were examined as well. Mechanical properties of the 1-cm-diameter samples were characterized through uniaxial compression test on the large-sized samples at a strain rate of 2.08 × 10^-4 s^-1 at room temperature. Scanning electron microscopy (SEM: CS3400) was used to examine the fracture surfaces.

3. Results and Discussion

To investigate the influence of composition fluctuation on the constitution of precipitated phases in the CuZr-based alloys, 1-cm-diameter cylindrical rods with different Ta contents were prepared and examined. As shown in Fig. 1, less than 0.3 at.% or more than 0.7 at.% Ta addition will cause the precipitation of some detrimental intermetallic compounds, such as CuZr₂ and Cu₁₀Zr₇ phases. These compounds may be harmful to the mechanical properties and result in the catastrophically brittle fracture under uniaxial stress. For the sample with 0.5 at.% Ta addition, only CuZr(B2) phase can be identified in the XRD pattern, as shown in Fig. 2. The inset of Fig. 2 is the appearance of the 1-cm-diameter sample. Hence, we can probably come to a conclusion that 0.5 at.% Ta addition can lead to the precipitation of single CuZr(B2) phase during the casting process at the present cooling rate.

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	Fig. 1. XRD patterns of the as-cast 1 cm-diameter rods for Cu_{46.15-0.5 x}Zr_{45.35-0.5 x}Al_7.5Sn₁Ta_x ( x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 at.%).

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	Fig. 2. XRD pattern of Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5 (Inset: the appearance of the 1-cm-diameter sample).

The difference in precipitated phases can also be confirmed by the SEM images. As shown in Fig. 3(a) and (b), the Ta-free sample contains CuZr(B2) phase (in dark gray), and some white dendrites uniformly distributed throughout the sample. Besides, some black phase exists irregularly with the composition of Zr_46.08±0.66Cu_46.65±0.20Al_7.28±0.54. The formation of these phases may be attributed to the cooling rate fluctuation in different parts of the samples during casting. Under the circumstance of more Ta addition (0.9 at.%), only a small amount of CuZr(B2) phase precipitated in the matrix, as presented in Fig. 3(c) and (d). Besides, excessive Ta addition induces the formation of packed crystalline phases near the center of the samples, whose distribution and size vary greatly throughout the composites. Therefore excessive Ta addition will weaken the glass-forming ability of the matrix alloys in this Cu–Zr–Al–Sn quaternary system seriously and lead to the precipitation of some detrimental phases.

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	Fig. 3. Microstructure of samples with different Ta addition: (a) 0, (b) 0, partial enlarged image, (c) 0.9 at.%, edge region, (d) 0.9 at.%, central part, (e) 0.5 at.%.

In comparison with the samples mentioned above, the microstructure of the Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5 alloy is relatively uniform. As shown in Fig. 3(e), spherical crystalline precipitates with diameters between 2 μm and 350 μm, which can be identified as the CuZr(B2) phase, are embedded uniformly in the featureless amorphous matrix (in light gray). The size distribution of the crystalline phase in this sample was revealed to be bimodal-like. The average diameter and volume fraction of the second phase can be determined as 52 μm and 32%, respectively.

TEM analysis was carried out in order to investigate the detailed structure of the precipitated phase and its beneficial effects on the mechanical properties. Fig. 4(a) shows the interface between the spherical phase and the amorphous matrix. Nanoscale crystals exist near the interface. The selected area electron diffraction (SAED) patterns (as shown in the inset) clearly show the typical halo ring of amorphous structure as well as the [001] zone axis diffraction of the CuZr(B2) phase. Fig. 4(b) shows that there are many sub-boundaries in the spherical CuZr(B2) phase. Compared with nanoscale crystals, such microscale spherical crystals can hinder the propagation of the shear bands effectively. Furthermore, the sub-boundaries full of defects (as shown in Fig. 4(c)) are suggested to be favorable for the nucleation of martensitic phase, and may make the martensitic transformation of CuZr(B2) easier to happen under stress.

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	Fig. 4. TEM images of the interface between CuZr(B2) phase and amorphous matrix (a) and the interior of CuZr(B2) phase (b) (Inset: The corresponding SAED patterns). The high-resolution transmission electron microscopy (HRTEM) image of a sub-boundary in the B2 phase (c).

Casting temperature is an important factor affecting the kind, volume fraction and distribution of the precipitates in the alloys. In this research, the effects of different casting temperatures for the alloy containing 0.5 at.% Ta were also examined. An infrared thermometer was used to measure the casting temperature through the observation window of the high frequency induction furnace. The XRD patterns of Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5 samples casted at different temperatures are shown in Fig. 5. It is seen that the optimal casting temperature to ensure the precipitation of single CuZr(B2) phase in the amorphous matrix is ∼1223 K. At higher or lower temperature, other detrimental phases will precipitate in the amorphous matrix.

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	Fig. 5. XRD patterns of Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5 samples casted at different temperatures.

To investigate the mechanism for the formation of large-scale BMGCs, characteristic temperatures of the ribbon samples with different Ta contents are measured by DSC under continuous heating process, and the corresponding curves are presented in Fig. 6(a). It turns out that the thermal behaviors keep almost unchanged with the addition of Ta. All these samples display a glass transition process followed by the crystallization and the eutectoid transformation of the crystalline phases from the equilibrium phases at low temperatures to the CuZr(B2) phase.

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	Fig. 6. (a) DSC curves of Cu_{46.15-0.5 x}Zr_{45.35-0.5 x}Al_7.5Sn₁Ta_x ( x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 at.%) ribbon samples, (b) melting process of corresponding master alloys, (c) solidification process of corresponding master alloys.

The melting and cooling processes of the master alloys were also measured and the curves are shown in Fig. 6(b) and (c). The liquidus temperature T_l decreases while the solidification temperature T_s increases with the increase of Ta content. All the characteristic temperatures are given in . T_f represents the offset eutectoid temperature of the CuZr(B2) phase. T_rg is the reduced glass temperature, which is equal to T_g/ T_l; γ is a thermal parameter which is usually used to evaluate the glass-forming ability of alloys, γ = T_x/( T_g + T_l). K, which can be expressed as K = T_f/ T_l is a parameter proposed to evaluate the forming tendency of the CuZr(B2) phase in the metastable CuZr-based alloys in terms of the competition among the vitrification, the precipitation of metastable CuZr(B2) phase and room-temperature equilibrium phases during quenching. Song et al. also pointed out that a larger K usually corresponds well with the easy formation of the CuZr(B2) phase in the CuZr-based BMGC ^[27].

Table 1. Thermal parameters of the Cu_{46.15-0.5 x}Zr_{45.35-0.5 x}Al_7.5Sn₁Ta_x samples with different Ta additions (0 ≤ x ≤ 0.9)

In this study, no definite relations can be identified among the parameter K as well as the other characteristic temperatures and the critical size of the samples with the change in the content of Ta. That is to say, in the present study, thermal properties may be not enough to reveal the reason for this size improvement. However, it is seen that appropriate amount of Ta addition can inhibit the precipitation of other crystalline phases besides the CuZr(B2) phase and increase the available size of the BMGC containing CuZr(B2) as the single crystalline phase.

Mechanical properties of the large-sized Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5 sample are measured using the 1-cm-diameter rods with the aspect ratio of ∼1.5. Fig. 7(a) shows the room-temperature compressive stress-strain curves. Unlike the case of most monolithic BMGs, the composite specimen exhibits obvious work-hardening behavior before fracture and undergoes a pronounced plastic deformation of ∼4.6%. The yield strength σ_y and fracture strength σ_f of the alloy are determined to be ∼1020 MPa and ∼1550 MPa, respectively. The inset of Fig. 7(a) shows the true stress-strain curve of the alloy. The strain-hardening exponent n is a useful parameter reflecting the work-hardening ability of materials during deformation. Here, n is calculated to be ∼0.292 for this specimen. Fig. 7(b) shows the fracture morphology of the composite sample. It is seen that the sample exhibits extensive vein-like patterns on its fracture surface.

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	Fig. 7. Compressive stress-strain curve (a) and fracture surface (b) of the as-cast 1 cm-diameter rods for Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5. (Inset: The corresponding true stress-strain curve).

4. Conclusion

In summary, centimeter-scale CuZr-based BMGC with the composition of Cu_45.9Zr_45.1Al_7.5Sn₁Ta_0.5 has been prepared successfully. The amount of Ta addition has a great influence on the types of the precipitated crystalline phases under the same casting conditions. The 0.5 at.% Ta addition can inhibit the precipitation of other crystalline phases rather than the CuZr(B2) phase during solidification. The present large-sized specimen shows excellent mechanical properties under room-temperature compression with visible plastic strain of ∼4.6% and obvious work-hardening behavior. The key point in fabricating large-sized CuZr-based BMGCs with good mechanical properties may be to prevent the precipitation of other crystalline phases such as the CuZr₂ or Cu₁₀Zr₇, which may be harmful to their mechanical properties. This work may be helpful to defeat the size limitations of the BMGC and provide useful guidance for the development of large-sized CuZr-based BMGCs.

References

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (NSFC, Granted Nos. 51161130526 and 51101004). Z.Q. Liu acknowledges the support of the IMR SYNL-T.S. Kê Research Fellowship.

The authors have declared that no competing interests exist.

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... IntroductionBulk metallic glasses (BMGs) have attracted great attention owing to their unique properties compared with their crystalline counterparts, such as high strength, high hardness, large elastic strain limit and good corrosion resistance^{[1], [2], [3], [4] and [5]} ...

1999

5.024

0.0

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3.941

0.0

2003

1.857

0.0

J. F.

Loffler

, Intermetallics, 11 (2003), pp. 529–540

Abstract In the last decade metallic glasses have regained considerable interest due to the fact that new glass-forming compositions have been found that have a critical cooling rate of less than 100 K/s and can be made glassy with dimensions of 1 cm or more. The development of such alloys with a very high resistance to crystallization of the undercooled melt has opened new opportunities for the fundamental study of both the liquid state and the glass transition. The availability of bulk specimens has enabled measurements of various physical, particularly mechanical, properties that were previously impossible. Furthermore, these alloys are progressively being used for engineering applications. In order to recognize this significant advancement in materials science, this new class of materials is commonly referred to as “bulk metallic glasses”. This article will first review the history of metallic glasses. The origins of glass formation are then discussed and thermophysical properties (crystallization, phase separation, viscosity and diffusion) are presented. Furthermore, the paper outlines magnetic and mechanical properties along with resulting applications and presents a new processing technique to discover bulk metallic glass compositions in Section 5.

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Eckert

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Abstract The compressive and tensile deformation, as well as the fracture behavior of a Zr 59 Cu 20 Al 10 Ni 8 Ti 3 bulk metallic glass were investigated. It was found that under compressive loading, the metallic glass displays some plasticity before fracture. The fracture is mainly localized on one major shear band and the compressive fracture angle, θ C , between the stress axis and the fracture plane is 43°. Under tensile loading, the material always displays brittle fracture without yielding. The tensile fracture stress, σ F T , is about 1.58 GPa, which is lower than the compressive fracture stress, σ F C (=1.69 GPa). The tensile fracture angle, θ T , between the stress axis and the fracture plane is equal to 54°. Therefore, both θ C and θ T deviate from the maximum shear stress plane (45°), indicating that the fracture behavior of the metallic glass under compressive and tensile load does not follow the von Mises criterion. Scanning electron microscope observations reveal that the compressive fracture surfaces of the metallic glass mainly consist of a vein-like structure. A combined feature of veins and some radiate cores was observed on the tensile fracture surfaces. Based on these results, the fracture mechanisms of metallic glass are discussed by taking the effect of normal stress on the fracture process into account. It is proposed that tensile fracture first originates from the radiate cores induced by the normal stress, then propagates mainly driven by shear stress, leading to the formation of the combined fracture feature. In contrast, the compressive fracture of metallic glass is mainly controlled by the shear stress. It is suggested that the deviation of θ C and θ T from 45° can be attributed to a combined effect of the normal and shear stresses on the fracture plane.

... However, the monolithic BMGs usually exhibit typical room-temperature brittleness and strain-softening phenomenon^{[6], [7] and [8]}, which have strictly limited their applications as structural materials ...

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Abstract The mechanical properties of amorphous alloys have proven both scientifically unique and of potential practical interest, although the underlying deformation physics of these materials remain less firmly established as compared with crystalline alloys. In this article, we review recent advances in understanding the mechanical behavior of metallic glasses, with particular emphasis on the deformation and fracture mechanisms. Atomistic as well as continuum modeling and experimental work on elasticity, plastic flow and localization, fracture and fatigue are all discussed, and theoretical developments are connected, where possible, with macroscopic experimental responses. The role of glass structure on mechanical properties, and conversely, the effect of deformation upon glass structure, are also described. The mechanical properties of metallic glass-derivative materials – including in situ and ex situ composites, foams and nanocrystal-reinforced glasses – are reviewed as well. Finally, we identify a number of important unresolved issues for the field.

1998

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... Recently, BMG composites (BMGCs), especially those with in-situ crystalline phases, have been prepared to circumvent some of these weaknesses of monolithic BMGs and several classes of BMGCs with excellent properties have been developed successfully^{[9], [10], [11], [12], [13], [14], [15], [16] and [17]} ...

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Abstract Ductile phase containing bulk metallic glass composites are prepared via an in situ method by rapid quenching of a homogenous Zr 56.2 Ti 13.8 Nb 5.0 Cu 6.9 Ni 5.6 Be 12.5 melt. The microstructure of the resulting two phase material is investigated by SEM, X-ray diffraction, and microprobe analysis. The composite material, as well as single phase materials with the corresponding matrix and second phase compositions, are tested in uniaxial tension and compression. Young's Modulus, shear modulus and Poisson ratios are analyzed by ultrasonic sound velocity measurements. The composite material demonstrates strongly improved Charpy impact toughness (by a factor of 2.5 compared to Vitreloy 1) and ductility (average fracture strain up to 8.3% in compression and 5.5% in tension). These remarkable improvements are explained by the effect of the mechanically soft and ductile second phase, which acts stabilizing against shear localization and critical crack propagation.

2006

0.588

0.0

2006

2.821

0.0

2007

1.857

0.0

2007

0.0

2008

38.597

0.0

2009

3.794

0.0

2005

3.794

0.0

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

2010

0.0

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

2010

14.829

0.0

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

2011

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Abstract The dependence of microstructure on the alloy composition and cooling rate of a series of (Zr 0.5 Cu 0.5 ) 100− x Al x ( x = 1, 2, 3 , … , 10 at.%) alloys was investigated in detail and explained in the framework of time–temperature–transformation diagrams. The relationship between the microstructures of bulk metallic glass (BMG) composites and their mechanical properties was characterized systematically. It was found that the addition of aluminum can promote the formation of the metastable austenitic CuZr phase, and composite structures with B2–CuZr particles can be formed in alloys containing 3–8% Al. Both the volume fraction and distribution of the reinforced B2 phase could greatly affect the deformation behavior, and the BMG composites with homogeneously distributed single B2–CuZr phase exhibited stable tensile ductility. Analysis indicates that the B2–CuZr austenite transformed into the B19′ martensite during deformation (i.e., stress-induced martensitic transformation), which accounts for the observed superior mechanical properties of the current BMG composites.

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

... In recent years, CuZr-based BMGCs have been studied widely due to their enhanced tensile properties and work-hardening ability^{[21] and [25]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

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2006

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E. S.

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Kim

, Acta Mater. , 54 (2006), pp. 2597–2604

Abstract Enhancement of plasticity and the occurrence of liquid-state phase separation have been investigated by partially substituting Zr with Y in Cu 46 Zr 47− x Y x Al 7 ( x = 0, 2, 5, 10, 15, 20, 25, 30, 35) alloys. Since Y has a positive enthalpy of mixing with Zr (+35 kJ/mol) in the liquid state, the alloy composition moves to the metastable miscibility gap of the two amorphous phases with increasing Y content. Phase separation into Y-rich and Zr-rich amorphous phases occurs during cooling from the liquid state when the Y content is above 15 at.%. The bulk amorphous alloys consisting of two phase-separated amorphous phases exhibit extreme brittleness, while the single-phase amorphous alloys containing 2–5 at.% of Y exhibit enhanced plasticity because of the introduction of chemical inhomogeneity in the amorphous matrix. The results indicate that the addition of an element having a positive enthalpy of mixing with the constitutive element in bulk amorphous alloys can increase the plasticity as well as the glass-forming ability, but for a limited composition range.

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

2009

1.857

0.0

Pauly

, J.

Das

, N.

Mattern

, D. H.

Kim

, J.

Eckert

, Intermetallics, 17 (2009), pp. 453–462

Abstract In the present study we investigate the phase formation and the thermal stability of Cu 50 Zr 50 − x Ti x (0 ≤ x ≤ 10) and (Cu 0.5 Zr 0.5 ) 100 − x Al x glass-forming alloys. Parameters indicating the glass-forming ability (GFA) are calculated from isochronal and isothermal calorimetric experiments. A high Ti content in the Cu–Zr–Ti alloys causes the precipitation of a metastable ternary Laves phase (C15), which does not form in Cu–Zr–Al. Accompanied with it is a significant drop in the activation energy of crystallization. Also the supercooled liquid region (Δ T x = T x − T g ), the reduced glass transition temperature ( T rg = T g / T liq ), and the γ parameter ( γ = T x /( T g + T liq )) ( T x : crystallization temperature, T g : glass transition temperature and T liq : liquidus temperature) are sensitive to the change in the crystallization sequence. The fragility values calculated are believed to overestimate the GFA of the investigated alloys. Careful selection of the alloy composition enables the targeted precipitation of different crystalline phases.

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

2012

1.857

0.0

... And the crystalline phase may undergo the martensitic transformation from B2 to B19′ phase during deformation^{[18], [19], [20], [21], [22], [23] and [24]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

2012

3.941

0.0

... In recent years, CuZr-based BMGCs have been studied widely due to their enhanced tensile properties and work-hardening ability^{[21] and [25]} ...

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

... Volume fraction and size distribution of crystalline phases in the composites were estimated according to the images of the cross-section surfaces ^{[21] and [25]} ...

2012

0.0

... Besides the mechanisms of their formation and deformation, the adjustment of their microstructure has also been studied systematically^{[19], [20], [21], [22], [23], [24], [25] and [26]} ...

2011

3.941

0.0

K. K.

Song

, S.

Pauly

, Y.

Zhang

, P.

Gargarella

, R.

, N. S.

Barekar

, U.

Kuhn

, M.

Stoica

, J.

Eckert

, Acta Mater. , 59 (2011), pp. 6620–6630

Abstract In the present work we systematically investigated the formation of high-temperature B2 CuZr intermetallics in 36 metastable CuZr-based alloys. The results demonstrate that a B2 CuZr solid-phase transformation exists at high temperature. Based on continuous heating transformation diagrams the CuZr-based alloys can be classified into three different types, related to the precipitation and stability of the B2 phase. A new prediction strategy for the formation of different sized CuZr-based shape memory bulk metallic glass composites (BMGC) is proposed by considering the competition between vitrification, the precipitation of metastable B2 CuZr and room-temperature equilibrium phases. These insights are condensed into a new parameter, K = T f / T L , where T f and T L are the final temperature of the B2 CuZr phase transformation during heating and the liquidus temperature of the alloy, respectively, which is suggested to predict and select a compositional region of different sized BMGC. This new approach could be of great significance for the development of metastable CuZr-based shape memory alloys with enhanced deformability.

... Although previous reports about pinpointing the formation of BMGCs may provide some meaningful guidance^[27], the dimension of composite samples, containing CuZr(B2) as the single precipitated crystalline phase in the amorphous matrix, is still in millimeter scale ...

... also pointed out that a larger K usually corresponds well with the easy formation of the CuZr(B2) phase in the CuZr-based BMGC ^[27] ...