Abstract
Despite a wealth of experimental studies focused on determining and improving mechanical properties and development of fundamental understanding of underlying mechanisms behind nucleation and growth of ductile phase precipitates from melt in glassy matrix, still, there is dearth of knowledge about how these ductile phases nucleate during solidification. Various efforts have been made to address this problem such as experiments in microgravity, high resolution electron microscopy and observation in synchrotron light after levitation but none have proved out to be satisfactory. In this study, an effort has been made to address this problem by modelling and simulation. Current state of the art of development, manufacturing, characterisation and modelling and simulation of bulk metallic glass matrix composites is described in detail. Evolution of microstructure in bulk metallic glass matrix composites during solidification in additive manufacturing has been presented with the aim to address fundamental problem of evolution of solidification microstructure as a result of solute partitioning, diffusion and capillary action. An overview is also presented to explain the relation of microstructure evolution to hardness and fracture toughness. This is aimed at overcoming fundamental problem of lack of ductility and toughness in this diverse class of materials. Quantitative prediction of solidification microstructure is done with the help of advanced part scale modelling and simulation techniques. It has been systematically proposed that 2-dimensional cellular automaton (CA) method combined with finite element (for thermal modelling) tools (CA-FE) programmed on FORTRAN? and parallel simulated on ABAQUS? would best be able to describe this complicated multiphysics phenomenon in most efficient way. Focus is laid on quantification of methodology by which modelling and simulation can be adopted and applied to describe evolution of microstructure in this important class of materials. It is found that proposed methodology is meritorious.
Highlights
Discovered in 1960 by Duwartz et al [1] at Caltech, Metallic Glasses [2] 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 [3] [4] [5] [6]
Growth As soon as grain has nucleated, and its growth can be explained by special modified case of classical nucleation theory (CNT) for bulk metallic glass matrix composites (BMGMC) (A detailed treatment of modified Classical nucleation theory (CNT) for BMGMC is given in Appendix A) and its distribution can be explained by constitutional supercooling zone/Interdependence theory—a possibility which is still under investigation by author for suitability for additive manufacturing processes), it grows with an interface velocity which is a function of undercooling
Other defects and solidification microstructure serve as sites for heterogeneous nucleation (their effects in total solidification are to be considered in final model). Despite their recent popularity and emblem to be exploited as potential structural engineering material for extreme applications, still, an in-depth understanding of underlaying mechanisms responsible for formation of glass and nucleation of ductile phase during solidification in bulk metallic glass and their composites is at an arm’s length from the limit of satisfaction
Summary
Discovered in 1960 by Duwartz et al [1] at Caltech, Metallic Glasses [2] 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 [3] [4] [5] [6]. This results in the formation of “glassy structure”. They are characterised by special properties such as glass forming ability (GFA), and metastability
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