Bulk Metallic Glasses and Their Composites

Additive Manufacturing and Modeling and Simulation

Muhammad Musaddique Ali Rafique

• Publisher: De Gruyter
• Year: 2021
• ISBN:
  9783110747416
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The book provides a comprehensive state-of-the-art review on the topic of bulk metallic glass matrix composites and understanding of mechanisms of development of composite microstructure. It discusses mechanisms of formation and toughening both during conventional casting routes and additive manufacturing. The second edition encompasses new studies and highlights advancement in mechanical properties, characterization, processing and applications.

Section 1 Research significance and background

Discovered in 1960 by Duwartz et al. [1] at Caltech, metallic glasses emerged as a completely new class of materials exhibiting very high tensile strength, hardness, elastic strain limit and yield strength at relatively lower density as compared to steel and other high-strength alloys [2, 3, 4]. Yet, their use has not been able to get broad acceptance as a competing engineering material because of the lack of ductility and inherent brittleness of glassy structure [3]. This property becomes even more prominent at large length scales (bulk metallic glasses (BMG) – metallic glasses typically having thickness >1 mm) [5, 6, 7, 8] as prominent catastrophic failure mechanisms (shear band) dominate [9, 10, 11]. This severely limits their application toward use in making large-scale machinery components. This disadvantage can be overpowered by inducing plasticity in a glassy structure while retaining its high strength at the same time [12, 13, 14, 15]. This can be done by various mechanisms, including exploitation of intrinsic ability of glass to exhibit plasticity at very small (nano) length scale [16, 17], introduction of external impulse (obstacles) to shear band formation and propagation (ex situ composites) [18, 19], self or externally assisted multiplication of shear bands [11, 20], formation of ductile phases in brittle glassy matrix during solidification (in situ composites) [21, 22, 23, 24] and transformation inside a ductile crystalline phase, for example, B2–B19′ transformation in Zr-based systems (stress/transformation-induced plasticity) [25, 26, 27, 28]. The later approach (formation of ductile phase in brittle glass) takes into account the nucleation of secondary (ductile) phase either during solidification in situ [29, 30, 31, 32, 33, 34, 35] or heat treatment of solidified glassy melt (devitrification/relaxation) [36, 37, 38, 39, 40, 41, 42, 43, 44] and forms the basis of ductile BMG composites.

Although considerable progress has been made in advancing “as-cast” sizes in BMG and their composites, still maximum possible diameter and length, which has been produced by conventional means till date [45], is far from the limit of satisfaction to be used in any structural engineering application. This is primarily associated with mechanical cooling rate achievable as a result of quenching effect from water-cooled walls of Cu container which in itself is not enough to overcome critical cooling rate (R_c) of an alloy (~ 0.067 K/s [45]) to produce a uniform large bulk glassy structure. In addition to this, occurrence of this bulk glassy structure is limited to compositions with excellent inherent glass-forming ability (GFA) [46, 47]. This is not observed in compositions that are strong candidates to be exploited for making large-scale industrial structural components [26, 48, 49, 50, 51, 52, 53, 54, 55, 56] with higher critical cooling rates (R_c) (10 K/s [49]). This poses a limitation to this conventional technique and urges the need of advanced manufacturing method that does not encompass these shortcomings. Additive manufacturing (AM) has emerged as a potential technique [57, 58] to fulfill this gap and produce BMG matrix composites [59, 60] in a single step across a range of compositions virtually covering all spectrums [61, 62, 63, 64]. It achieves this by exploiting very high cooling rates available in a very short period transient liquid melt pool [65, 66, 67] in a small region where high-energy source laser (LSM (laser surface melting)/laser surface forming LSF (solid), selective laser melting/LENS^® (powder) or electron beam melting) strikes the sample. This, when coupled with superior GFA of BMG matrix composites (BMGMC), efficiently overcomes the dimensional limitation as virtually any part carrying glassy structure can be fabricated. In addition, incipient pool formation [67] and its rapid cooling result in extremely versatile and beneficial properties in final fabricated part such as high strength, hardness, toughness, controlled microstructure, dimensional accuracy, consolidation and integrity. The mechanism underlying this is layer-by-layer (LBL) formation, which ensures glass formation in each layer during solidification before proceeding to the next layer. That is how a large monolithic glassy structure can be produced. This LBL formation also helps in development of secondary phases in a multicomponent alloy [68, 69, 70] as a layer preceding fusion layer (which is solidified) undergoes another heating cycle (heat treatment) below melting temperature (T_m) somewhat in the nose region of TTT (time–temperature transformation) diagram [59], which not only assists in phase transformation [41, 43] but also helps in the increase in toughness, homogenization and compaction of part. This is a new, promising and growing technique of rapidly forming metal [71], plastic [72], ceramic or composite [73] parts by fabricating a near-net shape out of raw materials either by powder method or wire method (classified on the basis of additives used). The movement of energy source (laser or electron beam) is dictated by a CAD geometry which is fed to a computer at the back end and maneuvered by computerized numerical control (CNC) [74, 75] system. Process has a wide range of applicability across various industrial sectors ranging fro...

Table of contents

• Title Page
• Copyright
• Contents
• Section 1 Research significance and background
• Section 2 Bulk metallic glasses (BMGs) and bulk metallic glass matrix composites (BMGMCs)
• Section 3 Additive manufacturing (AM)
• Section 4 Modeling and simulation
• Section 5 Modeling and simulation of solidification phenomena during processing of BMGMC by additive manufacturing (AM)
• Appendix A: Heterogeneous nucleation and growth in very fluid alloys (as per CNT) [1064]
• Comparison
• Research gap
• Overall aims/research questions
• Methodology
• Exercise
• Design problems
• Index