Dynamics and Stability of Shear Banding in Metallic and Oxide Glasses

Metallic glasses (MGs), as a new emerging class of metallic materials, have attracted extensive scientific and technological interests because of their unique mechanical and physical properties, including extremely high strength, large elastic strain limit, superior magnetic properties, etc. In spite of these promising properties, their widespread applications are limited primarily due to the inhomogeneous deformation localized in extremely thin shear band (~10 nm), displaying catastrophic failure with little plasticity. Over the past years, remarkable efforts have been devoted to revealing the shear banding (SB) mechanism of MGs; however, most of them are based on macroscopic approaches with low instrument resolutions plus with the cast defects in macro-specimens, making the intrinsic behavior of SB blurred, thus the mechanism of SB is still far from fully understood, while, nanoindentation, with nanoscale resolution, offers us an excellent opportunity to tackle this nano-localized process. This proposed research is aiming at elucidating the physical origin of the dynamics and stability of SB. We intend to develop a scientific scheme to bridge the gap between the SB dynamic process and the atomic structure of MGs through a combination of the state-of-the-art experimental techniques and theoretical calculations. Based on the experimental and simulation outcomes from MGs, we plan to extend the research to SB of borosilicate glasses, with the ultimate goal to establish a unified SB theory for glass materials with amorphous structures.Relatively soft/ductile Zr50Cu40Al10 and strong/brittle Fe71Nb6B23 MGs will be chosen to investigate the fundamentals of the SB dynamics and stability through a systematical adjustment of loading stress, strain rate and test temperature during microcompression tests. Using high-resolution TEM and AFM rearrangement of atomic clusters in shear band will be scrutinized. Also, surface coating will be used to monitor SB dynamics and stability, and to enhance the plasticity of MGs. Furthermore, by extending the research to include borosilicate glasses, we will attempt to establish a unified SB theory for metallic and oxide glasses. Besides the systematic experimental studies, we will perform molecular dynamics simulations to probe the atomic-scale structural evolution during SB. These comprehensive investigations coupled with our core-shell structural model will allow us to approach the physical origin of SB dynamics and stability.The implementation of this proposal will expect to lead to an in-depth understanding the SB dynamics and stability of glass materials with amorphous structures. Furthermore, it will provide a scientific guidance for the design of ductile MGs for engineering use.