Bulk Metallic Glasses and Their Composites

Additive Manufacturing and Modeling and Simulation

Muhammad Musaddique Ali Rafique

• Publisher: Momentum Press
• Year: 2018
• Print ISBN: 9781947083844
• eBook ISBN: 9781947083851
• Topic: Technology & Engineering
• Subtopic: Industrial Engineering
• Index: Technology & Engineering

This book presents a comprehensive and holistic study of microstrucure evoution during solidification and additive manufacturin.g

Bulk metallic glasses and their composites have attracted a lot of attention lately in the scientific community owing to their excellent mechanical properties (combination of hardness, strength, and high elastic strain limit). However, they still lack toughness and tensile ductility and exhibit catastrophic failure upon tension. This can be overcome by various means, of which in situ introduction of ductile crystalline precipitates/phases during solidification proved to be the best.

Various studies have been carried out in the last two decades, which explain this phenomenon. However, there is a gap on how this can be achieved in modern additive manufacturing exploiting inherent nature of process. This book aims to bridge this gap. A comprehensive and holistic study is presented, documenting the step-by-step evolution of these materials since their inception till date, explaining the development of toughness in them by modeling and simulation of microstructure evolution during solidification and additive manufacturing.

SECTION 1

BULK METALLIC GLASSES AND BULK METALLIC GLASS MATRIX COMPOSITES

1.1 METALLIC GLASSES AND BULK METALLIC GLASSES/MONOLITHS

Metallic glasses (MG) (Chen 1974) may be defined as “disordered atomic-scale structural arrangement of atoms formed as a result of rapid cooling of complex alloy systems directly from their melt state to below room temperature with a large undercooling and a suppressed kinetics in such a way that the supercooled state is retained/frozen” (Güntherodt 1977; Greer 1995; Inoue 1995; Johnson 1999). This results in the formation of “glassy structure.” The process is very much similar to inorganic/oxide glass formation in which large oxide molecules (silicates/borides/aluminates/sulfides and sulfates) form a regular network retained in its frozen/supercooled liquid state (Matthieu 2016). The only difference is that MGs are comprised of metallic atoms rather than inorganic metallic compounds. Their atomic arrangement is based on a mismatch of atomic size and quantity (minimally three) (Hofmann and Johnson 2010) (described in the next section), is based on short-range order (Shi and Falk 2006; Mattern et al. 2009; Jiang and Dai 2010) to medium-range order (Sheng et al. 2006; Cheng et al. 2009; Zhang et al. 2014a) or long-range disorder (Inoue and Takeuchi 2011) (unlike metals—well-defined long-range order), and can be explained by other advanced theories/mechanisms (frustration [Nelson 1983], order in disorder [Nelson 1983; Sheng et al. 2006; Ma 2015], and confusion [Greer 1993]). Important features characterizing them are their amorphous microstructure and unique mechanical properties. Owing to the absence of dislocations, no plasticity is exhibited by bulk metallic glasses (BMGs). This results in very high yield strength and elastic strain limits as there is no plane for material to flow (by conventional deformation mechanisms). From a fundamental definition point of view, MGs are typically different from BMG in that the former has fully glassy (monolithic) structure for thicknesses less than 1 mm, while the latter is glassy (monolithic) in greater than 1 mm (Drehman et al. 1982; Kui et al. 1984). To date the largest BMG made in “as cast” condition is 80 mm in diameter and 85 mm in length (Nishiyama et al. 2012). There are reports of making large thin castings as casing of smart phone but they are typically less than 1 mm (Qiao et al. 2016). Furthermore, they are characterized by special properties such as glass-forming ability (GFA) and metastability (which will be described in following sections).

1.2 THREE LAWS

The formation and stability of BMG (even in metastable condition) is described by their ability to retain glassy state at room temperature. Although the understanding of glass and glassy structure was established much earlier, it was very difficult to form homogeneous, uniform glassy structure across whole section thickness at room temperature until recently. Only alloys of very narrow compositional window cooled at extremely high cooling rate can form glassy structure (Klement et al. 1960; Turnbull 1969; Chen 1974, 1980; Drehman et al. 1982). Any deviation from any of these parameters severely hampers the retention of glassy state and crystallization occurs (Akhtar et al. 1982a, 1982b; Akhtar and Misra 1985). This property is known as GFA (Inoue, Zhang, and Masumoto 1993). This is the single most important property in MG family of alloys which governs their formation and evolution. GFA has been increasingly studied and considerable progress has been made in its improvement (Donald and Davies 1978; Lu et al. 2008; Wang et al. 2012b; Yi et al. 2016b) by alterations in both composition and window of processing condition (Park and Kim 2005; Chen 2011; Inoue and Takeuchi 2011). Now, alloys having multicomponent composition can be cast in glassy state even at slow cooling rate owing to their superior GFA (Peker and Johnson 1993; Yi et al. 2016; Jia et al. 2006a; Cheng et al. 2008; Park et al. 2008; Miracle et al. 2010; Guo et al. 2016), which in turn is governed by various theories (Donald and Davies 1978; Li et al. 1997, 2011, 2012, 2014a; Fan et al. 2001; Lu and Liu 2002, 2004; Kim et al. 2003; Xu et al. 2004; Park et al. 2008; Yang et al. 2010; Wu et al. 2014a; Shen et al. 2015) and analytical models (Zhang et al. 2013b; Amokrane et al. 2015).

Fundamentally, research over a period of time has yielded three basic laws that are now considered universal for the formation of any BMG system (Hofmann and Johnson 2010). These are described below. Any glass-forming system consists of elements that must

1. Be three in number (at minimum). (Elements greater than 3 are considered beneficial.)

2. Differ in their atomic size by 12% among three elements. (Atoms of elements with large size are considered to exhibit superior GFA.)

3. Have negative heat of mixing among three elements. (This ensures tendency to demix or confuse (Greer 1993) ensuring retention of glassy structure at room temperature.)

This results in new structure with high degree of densely packed atomic configurations, which, in turn, results in completely new atomic configuration at the local level with long-range homogeneity and attractive interaction. In general BMG or bulk glassy alloy (BGA) is typically designed around (1) alloy systems that exhibit a deep eutectic, which decreases the amount of undercooling needed to vitrify the liquid, and (2) alloys that exhibit a large atomic size mismatch, which creates lattice stresses that frustrate crystallization (Hofmann and Johnson 2010). An important way to arrive at optimum glass-forming composition and then selecting alloying elements is based on proper choice of eutectic or off-eutectic composition, diameter, and heat of mixing (Inoue and Takeuchi 2011). These laws were first proposed by Douglas C. Hoffmann and his supervisor at Caltech (Hofmann and Johnson 2010) and Prof. Akisha Inoue at WPI IMR, Tohoku University, Japan (Inoue and Takeuchi 2011) independently.

1.3 CLASSIFICATION

As proposed by Prof. Inoue (Inoue and Takeuchi 2002, 2011; Inoue et al. 2006), BMG can be broadly classified into three types (Figure 1.1):

1. Metal–Metal Type

2. Pd–Metal–Metalloid Type

3. Metal–Metalloid Type

This classification is based on the ease with which one group of metals reacts with the other group to finally evolve a glassy structure, which in turn is chosen by various rules such as chemical affinity, atomic size, electronic configuration, etc. Their proposed atomic arrangement, size, and crystal structure are shown in Figure 1.1. Metal–metal type glassy alloys are composed of icosahedral-like ordered atomic configurations. They are exemplified by Zr–Cu–Al–Ni and Zr–Cu–Ti–Ni–Be type systems. Pd–transition metal–metalloid type glassy alloys consist of high dense packed configurations of two types of polyhedra of Pd–Cu–P and Pd–Ni–P atomic pairs. Their typical examples are Pd–Cu–Ni–P systems. Metal–metalloid type glassy alloys have network-like atomic configurations in which a disordered trigonal prism and an anti-Archimedean prism of Fe and B are connected with each other in face- and edge-shared configuration modes through glue atoms of Ln and early transition metals (ETM) of Zr, Hf, and Nb. Their typical examples are Fe–Ln–B and Fe–(Zr, Hf, Nb)–B ternary systems. These icosahedral-, polyhedral-, and network-like ordered atomic configurations can effectively suppress the long-range rearrangements of the constituent elements that are necessary for onset of crystallization process. Among the three structures described, the second and third types have similarity that they both contain trigonal prism structure but are different in that the latter forms a well-developed connected structure of prisms by sharing their vertices and edges, which results in highly stabilized supercooled liquid leading to the formation of BGA even at very slow cooling solidification processes (Inoue and Takeuchi 2011). From an engineering standpoint, BGA adopts another system of classification that is based on their applicability. They are classified into seven types which in turn are grouped into two main types based on their behavior in phase diagrams. These are described as follows:

a. Host metal base type: Zr–Cu–Al–Ni, Fe–Cr–metalloid, Fe–Nb–metalloid, and Fe–Ni–Cr–Mo–metalloid systems and

b. Pseudo-host metal base type: Zr–Cu–Ti–Ni–Be, Zr–Cu–Ti–(Nb, Pd)–Sn, and Cu–Zr–Al–Ag systems

Figure 1.1. Classification of BGAs (Inoue and Takeuchi 2002, 2011).

It can be observed that Fe and Zr comprise the most important materials for practical use. Further subclassification of Zr-based BMG is also proposed by Prof. Inoue whose details can be found in cited literature (Inoue and Takeuchi 2011).

1.4 IMPORTANT CHARACTERISTICS

The formation and stability of BMGs are governed by their ability to form complex network and then retain this below room temperature. This is best described by its intrinsic properties specific to these alloy systems. These are GFA and metastability.

1.4.1 GLASS-FORMING ABILITY

As described in Section 1.2, GFA may be defined as “inherent, intrinsic ability of a multicomponent system to consolidate in state of low energy in such a way that glass formation is promoted and crystallisation is retarded.” This single unique parameter is effectively used to identify and design a range of glassy alloys. The ...

Table of contents

• Cover
• Half Title Page
• Title Page
• Copyright Page
• Contents
• Acknowledgments
• Research Significance and Background
• Section 1 Bulk Metallic Glasses and Bulk Metallic Glass Matrix Composites
• Section 2 Additive Manufacturing
• Section 3 Modelling and Simulation
• Section 4 Modeling and Simulation of Solidification Phenomena during Processing of BMGMC by Additive Manufacturing
• Appendix A
• Appendix B
• Comparison
• Research Gap
• Overall Aims/Research Questions
• Methodology
• References
• About the Author
• Index