Elsevier

Acta Materialia

Volume 48, Issue 1, 1 January 2000, Pages 279-306
Acta Materialia

Stabilization of metallic supercooled liquid and bulk amorphous alloys

https://doi.org/10.1016/S1359-6454(99)00300-6Get rights and content

Abstract

Bulk metallic materials have ordinarily been produced by melting and solidification processes for the last several thousand years. However, metallic liquid is unstable at temperatures below the melting temperature and solidifies immediately into crystalline phases. Consequently, all bulk engineering alloys are composed of a crystalline structure. Recently, this common concept was exploded by the findings of the stabilization phenomenon of the supercooled liquid for a number of alloys in the Mg-, lanthanide-, Zr-, Ti-, Fe-, Co-, Pd–Cu- and Ni-based systems. The alloys with the stabilized supercooled liquid state have three features in their alloy components, i.e. multicomponent systems, significant atomic size ratios above 12%, and negative heats of mixing. The stabilization mechanism has also been investigated from experimental data of structure analyses and fundamental physical properties. The stabilization has enabled the production of bulk amorphous alloys in the thickness range of 1–100 mm by using various casting processes. Bulk amorphous Zr-based alloys exhibit high mechanical strength, high fracture toughness and good corrosion resistance and have been used for sporting goods materials. The stabilization also leads to the appearance of a large supercooled liquid region before crystallization and enables high-strain rate superplasticity through Newtonian flow. The new Fe- and Co-based amorphous alloys exhibit a large supercooled liquid region and good soft magnetic properties which are characterized by low coercive force and high permeability. Furthermore, homogeneous dispersion of nanoscale particles into Zr-based bulk amorphous alloys was found to cause an improvement of tensile strength without detriment to good ductility. The discovery of the stabilization phenomenon, followed by the clarification of the stabilization criteria of the supercooled liquid, will promise the future definite development of bulk amorphous alloys as new basic science and engineering materials.

Section snippets

History and alloy components of bulk amorphous alloys

Since the first synthesis of an amorphous phase in the Au–Si system by a rapid solidification technique in 1960 [1], a great number of amorphous alloys has been produced for the last three decades. It is well known that Fe-, Co- and Ni-based amorphous alloys found before 1990 require high cooling rates above 105 K/s for glass formation and the resulting sample thickness is limited to less than about 50 μm [2]. As exceptional examples, one can observe that Pd–Ni–P and Pt–Ni–P amorphous alloys have

Structure of bulk amorphous alloys and reasons for high glass-forming ability

Firstly, the reason for the stabilization of the supercooled liquid for the alloys belonging to the groups (i)–(iv) is discussed. All the alloy systems in these groups are based on the following three empirical rules 17, 18, 19, 20, 21: (1) multicomponent systems consisting of more than three elements; (2) significant difference in atomic size ratios above about 12% among the three main constituent elements; and (3) negative heats of mixing among the three main constituent elements. We want to

Production of bulk amorphous alloys

By choosing the above-described multicomponent alloy systems, we can produce bulk amorphous alloys by using two kinds of production techniques of solidification and consolidation 17, 18, 19, 20, 21. As a solidification technique, one can list water-quenching, copper-mold casting, high-pressure die casting, arc melting, unidirectional melting, suction casting and squeeze casting. Bulk amorphous alloys are also produced by hot pressing and warm extrusion of atomized amorphous powders in the

Mechanical properties

In addition to the importance of basic science, it is important in applications as engineering materials to clarify the mechanical properties of bulk amorphous alloys. Figure 8 shows the relationship between the tensile fracture strength (σf) and Young's modulus (E) for the cast bulk amorphous Zr–Ti–Al–Ni–Cu alloys in sheet and cylinder forms with thicknesses (or diameters) of 1–5 mm [21]. The bulk amorphous alloys have high σf of 840–2100 MPa combined with E of 47–102 GPa which depend on alloy

Corrosion resistance

When bulk amorphous alloys for their good static and dynamic mechanical properties are used as structural materials, it is essential for the bulk amorphous alloys to have good corrosion resistance in various kinds of corrosive solutions. There have been no data published on the corrosion resistance of Zr-based bulk amorphous alloys in any kinds of corrosive solution. We examined the corrosion resistance of melt-spun amorphous alloys in Zr–TM–Al–Ni–Cu (TM=Ti,Cr,Nb,Ta) systems in HCl and NaCl

High strain-rate superplasticity

As described above, the bulk amorphous alloys have a wide supercooled liquid region of more than 60 K before crystallization. Figure 14 shows the change in viscosity with reduced temperature (Tr=T/Tm) for the Pd40Cu30Ni10P20 amorphous alloy [49]. The data of SiO2 glass are also shown for comparison. The viscosity of the Pd-based amorphous alloy has much larger temperature dependence as compared with SiO2 glass, indicating that the Pd-based amorphous alloy belongs to the fragile type glass which

Magnetic properties

Based on the three empirical rules for achievement of high GFA, a new bulk amorphous alloy with ferromagnetism at room temperature has been developed. As described in Section 1, soft ferromagnetic bulk amorphous alloys have been synthesized in multicomponent Fe–(Al,Ga)–(P,C,B,Si) [10], Co–Cr–(Al,Ga)–(P,B,C) [57], Fe–(Co,Ni)–(Zr,Nb,Ta)–B [11] and Co–Fe–(Zr,Nb,Ta)–B [58] systems. This section describes the relationship of soft magnetic properties of new Fe- and Co-based amorphous alloys with high

Formation and structures

The single-stage crystallization mode typical for bulk amorphous alloys also implies that the amorphous phase containing homogeneously nanocrystalline particles is not formed. It has previously been pointed out that the mixed structure consisting of nanoscale crystalline particles embedded in an amorphous phase is formed in the satisfaction of the four following criteria [69]:

  • 1.

    multistage crystallization process;

  • 2.

    existence of homogeneous nucleation sites in an amorphous phase;

  • 3.

    suppression of growth

Formation and mechanical properties of bulk-clustered amorphous alloys

It was shown in the previous section that the most important point in obtaining high Vf for the mixed-phase alloys is attributed to the good ductility of the remaining amorphous phase. The above-described nanostructured amorphous alloys were obtained by annealing-induced partial crystallization in the supercooled liquid region, followed by water-quenching. In addition to the annealing treatment, as another route to producing the similar nanostructured amorphous structure, one can observe a

Applications and conclusions

Table 8 summarizes fields of application in which the bulk amorphous alloys have expected uses. As particularly important application fields, one can list machinery/structural materials, magnetic materials, acoustic materials, somatologic materials, optical machinery materials, sporting goods materials and electrode materials. Finally, it is pleasing to introduce a successful example of a real application of bulk amorphous alloys as sporting goods materials. As exemplified in Fig. 39, the

Acknowledgements

This work is partly supported by the Inoue Superliquid Glass Project of Exploratory Research for Advanced Technology, Japan Science and Technology Corporation (JST).

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