Abstract

Bulk metallic glasses (BMGs) and their composites (BMGMC) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very high elastic strain limit. However, they suffer from a lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which render them to failure without appreciable yielding owing to mechanisms of rapid movement of shear bands all throughout the volume of the material. This severely limits their use in fabricating structural and machinery parts. Various mechanisms have been proposed to counter this effect. Introduction of secondary ductile phase in the form ofin-situnucleating and growing dendrites from melt during solidification have proved out to be best solution of this problem. Nucleation and growth of these ductile phases have been extensively studied over the last 16 years since their introduction for the first time in Zr-based BMGMC by Prof. Johnson at Caltech. Data about almost all types of phases appearing in different systems have been successfully reported. However, there is very little information available about the precise mechanism underlying their nucleation and growth during solidification in a copper mould during conventional vacuum casting and melt pool of additively manufactured parts. Various routes have been proposed to study this including experiments in microgravity, levitation in synchrotron light and modelling and simulation. In this report consisting of two parts which is a preamble of author’s PhD Project, a concise review about evolution of microstructure in BMGMC during additive manufacturing have been presented with the aim to address fundamental problem of lack in ductility along with prediction of grain size and phase evolution with the help of advanced modelling and simulation techniques. It has been systematically proposed that 2 and 3 dimensional cellular automaton method combined with finite element (CAFE) tools programmed on MATLAB® and simulated on Ansys® would best be able to describe this phenomenon in most efficient way. Present part consists of general introduction of bulk metallic glass matrix composites (BMGMC), problem of lack of ductility in them, measures to counter it, success stories and their additive manufacturing.

Highlights

  • T secondary ductile phase in the form of in-situ nucleating and growing dendrites from melt during solidification have proved out to be best solution of this problem

  • R microstructure in BMGMC during additive manufacturing have been presented with the aim to address fundamental problem of lack in ductility along with prediction of grain size and phase evolution with the help of advanced modelling and simulation techniques

  • Bulk metallic glasses (BMGs) and their composites (BMGMCs) are relatively new class of materials which have recently emerged on the surface of science and technology and gained attention due to their unique properties [10, 139, 228, 375]

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Summary

Bulk Metallic Glasses and Bulk Metallic Glass Matrix Composites

Metallic glasses (MGs) [5] may be defined as disordered atomic – scale structural arrangement of atoms formed as a result of rapid cooling of binary and multicomponent alloy systems directly from their molten state to below their glass transition temperature with a large undercooling and suppressed kinetics of nucleation in such a way that the supercooled liquid state is retained / frozenin [113,114,115,116] This results in the formation of a “glassy structure”. An important way to arrive at an optimum glass forming composition and selecting alloying elements is based on the proper choice of an eutectic or off-eutectic composition, atomic diameter and heat of mixing [4]. These laws were first proposed by Prof. Hoffmann at Caltech [118] but in essence the message they contain remain same

Classification
Important characteristics
Metastability
Common microstructures
Mechanical Properties
3.1.10 Very recent trends and triumphs
3.1.12 Present Research – Bridging the gap
3.1.13 Bulk Metallic Glass Matrix Composites by Additive Manufacturing
Conclusion
D Engineering: R
Findings
E Laser Epitaxy for Turbine Engine Hot-Section Component Repair
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