**1. Introduction**

366 Heat Treatment – Conventional and Novel Applications

Solids, 352 (42-49) (2006) 5199-5204.

Communications 111 (1999) 723-728.

State Comunications, 117, 733-737 (2001).

275-277 (1998) 738-741.

(2006) 1137-1141.

(1993).

9687-9693.

2550.

[19] MPF Graça, MGF Silva, ASB Sombra and MA Valente, Journal of Non-Crystalline

[20] T. Cardinal, E. Fargin, G. Le Flem, S. Leboiteux, J. Non-Cryst. Solids 222 (1997) 228-234. [21] A.C:V de Araujo, I.T. Weber, W.D: Fragoso, C.M. Donegá, J. of Alloys and Compounds

[22] Y.D. Juang, S.B. Dai, Y.C. Wang, W.Y. Chou, J.S. Hwang, M.L. Hu, w.S. Tse, Solid State

[24] A A Lipovskii, V.D. Petrikov, V.G. Melehin, D.K. Tagantsev, B.V. Tatarintsev, Solid

[27] A.K. Jonscher, "Dielectric relaxation in solids", Chelsea Dielectrics Press, London, 1983. [28] H.G. Kim, T. Komatsu, R. Sato and K. Matusita , J. Non-Cryst. Solids, 162, 201-204

[33] A. Ridah, P. Bourson, M.D. Fontana, G. Malovichko, J. Phys. Condens. Matter 9 (1997)

[36] MPF Graça, MGF Silva and MA Valente, Journal of Materials Science, 42(8) (2007) 2543-

[37] Glasses with ferroelectric phases, M.A. Valente and M.P.F. Graça, IOP Conf. Series:

[38] E.B. de Araujo, J.A.M. de Abreu, R.S. de Oliveira, J.A.C. de Paiva, A.S.B. Sombra,

[23] N. Shibata, M. Horigudhi, T. Edahino, J. Non-Cryst. Solids, 45 (1981) 115-126.

[25] J.R. Macdonald, "Impedance spectroscopy", John Wiley & Sons, New York, 1987. [26] M.P.F. Graça, M.A. Valente, M.G. Ferreira da Silva, Journal of Materials Science, 41 (4)

[29] M.M. Aboulleil, F.J. Leonberger, J. Am. Ceram. Society, 72 (1989) 1311-1320. [30] R.Claus, G.Borsel, E. Wiesendanger, L.Steffan, Phys. Ver. B, 6(12) (1972) 4878-4879.

[31] A. Jayaraman, A. A. Ballman, J. Appl. Phys., 60 (3) (1986) 1208-1210. [32] J.G. Scott, S. Mailis, C.L. Sones, R.W. Eason, Appl.Phys. A, 2003.

[35] J. Kincs, S. W. Martin, Physical Review letters, 76 (1) (1996) 70-73.

[34] W. Vogel, Glass Chemistry, Springer, 2nd edition, 1994.

Materials Science and Engineering 2 (2009) 012012.

Canadian Journal of Physics, 75 (1997) 747-758. [39] C. Hong, D.E. Day, J. Mater. Sci., 14, 2493-2499 (1979). [40] C. Hong, D.E. Day, J. Am. Ceram. Soc., 64:2, 61-67 (1981). Metals play a significant role in human life since the Bronze Age. Metals' important advantages include higher toughness and predictable fracture behavior in all directions, which are fundamentally essential for engineering applications. In coarse-grain polycrystalline alloys, the plastic deformation is mediated by dislocations within the grains. Micromechanisms of dislocation-based plasticity have been well investigated. Taylor, Polanyi, and Orowan's speculative models and Hirsch and Whelan's experimental results clearly demonstrate that the existence of dislocations in the metals, like a double-edged sword, enhances the ductility, while reducing the theoretical strengths of most of the metallic crystalline systems [1]. However, the toughness depends on the integration of both strength and ductility. Hence, designing of advanced metallic materials to answer the challenging strength-ductility dilemma become an urgent call. There is natural limitation on the conventional polycrystalline metallic alloys. In practical uses, there are always some inherent defects in the crystalline phases, which degrade the alloys properties. Recently, the limitation of the crystalline-material strength was passed when the metallic alloys with amorphous structures were successfully synthesized in many material systems through advanced manufacturing methods[2]. Although most of the metallic elements exiting in the nature are present with crystalline structures which are the most stable structures with the lowest energy state, sometimes they can be made by various ways into metastable amorphous solid forms, such as rapid quenching techniques [3-5], mechanical alloying [6-8], accumulative roll bonding [9-12], and vapor condensation [13]. The characteristics of the mechanical, thermodynamic properties of such category of metallic materials are very similar to ceramic glasses, and thus they are also called as metallic glasses. Moreover, by introducing specific crystalline phases, such as crystalline dendrites, in an amorphous matrix, bulk metallic glass-

© 2012 Huang et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons. org/licenses/by/3. 0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Huang et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

composite materials demonstrate the improved plasticity and toughness, compared with monolithic amorphous materials [14]. These metallic systems have the capacity of revolutionizing current metal-forming technologies and manufacturing industries.

Cooling – As a "Heat Treatment" for the Mechanical Behavior of the Bulk Metallic Glass Alloys 369

Fe-, Pd-, Cu-, Ti- and Ni- based systems. The Inoue group found exceptional glass forming ability in La-Al-Ni and La-Al-Cu ternary alloys system [24]. By casting the alloy melt in water-cooling Cu molds, the cylindrical samples with diameters up to 5 mm or sheets with similar thicknesses were made fully glassy in the La55Al25Ni20 alloy. Similarly, the La55Al25Ni10Cu10 alloy, fabricated by the same method, was even big with a diameter up to 9

In the 1990s, the Inoue group further developed a series of multicomponent Zr-based bulk metallic glasses, such as Zr-Cu-Ni, Zr-Cu-Ni-Al, etc. , along with Mg-based, e. g. Mg–Cu–Y and Mg–Ni–Y alloys, all exhibiting a high Glass Forming Ability (GFA) and thermal stability [26-29]. For one of the Zr-based BMGs, Zr65Al7. 5Ni10Cu17. 5, the critical casting thickness was up to 15 mm, and the largest critical casting thickness was 72 mm in the Pd–Cu–Ni–P family [30]. With Inoue's advancement of the aforementioned bulk metallic glass alloys, the BMGs were no longer laboratory curiosity. The possibility of promising engineering applications became reality. One of the examples was that the Zr-based bulk metallic glasses were applied in the industries just three years after it was invented [31]. Subsequently, a set of the very famous empirical rules in order to direct the selection of alloying elements and composition of glass forming alloys have been summarized by Inoue and Johnson as follows [32-33]: (1) Multicomponent alloys with three or more elements; (2) More than 12% atomic radius difference among them; (3) Negative heat of mixing between constituent elements; (4) The deep eutectic rule based on the Trg criterion. These rules concluded critical criteria for the design of the BMGs until 1999. However, the exception was found in the binary systems, such as the Ni-Nb [34], the Ca-Al [35] the Zr-Ni [36], and the Cu-Zr [37-38] alloys. The above systems can also produce BMGs with the size up to several millimeters without the limitations of the eutectics. In summary, the formation mechanism and criteria for the binary BMGs might not follow the traditional multi-component systems. These results suggest that there are many other potential forming systems of the metallic glasses to be

**3. How to describe the mechanical behavior of the bulk metallic glasses** 

Over the past four decades, considerable research efforts have been made on the BMGs due to their potential opportunity based on the high yield strength, relatively high fracture toughness, low internal friction, high fatigue resistance, as well as better wear and corrosion resistance [31-32, 39]. Although the bulk metallic glasses (BMGs) are one of such species of materials which are considered for future industrial applications, the insufficient plastic deformation at room temperature is still the Achilles' hell for the industrial applications regardless of its highly scientific value. In general, metallic glasses (MGs) are disordered materials which lack the periodicity of long range ordering in the atom packing, but the atomic arrangement in amorphous alloys is not completely random as liquid. In fact, many scholars believe that amorphous structures are composed of short range ordering, such as icosahedra clusters or other packing forms related to the intermetallic compounds that would form in the corresponding equilibrium phase diagram [40-41]. The short range order is identified as a structure consisting of an atom and its nearest neighbors perhaps two or

mm.

discovered.
