Atomistic scale modeling of metallic glass-based hybrid composites with tailored design

• Applicant: Daniel Sopu, Ph.D.
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Theoretical Condensed Matter Physics
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 318962047

A straightforward strategy to improve the plasticity of bulk metallic glasses (BMGs) is to synthesize dual-phase BMG composites. The understanding of structure-property correlations in BMG composites is of fundamental interest to establish guidelines and predictions for alloy design by cross-linking relationships between chemical composition, structure, alloy stability, and possible transformations. Although there is a sustained experimental work in literature on the macroscopic plasticity of smart composite materials reinforced with a crystalline phase, an elaborated theoretical model to provide an atomistic understanding of the underlying mechanisms does not exist.The subject of the present proposal deals with an ambitious work on molecular dynamics (MD) simulations of nanostructure-property optimization in bulk CuZr-based metallic glass composites. The primary goal of this project is to explore the possibility to prevent strain localization by designing the composite structure so that the plastic flow will proceed very slowly at the early embryonic stage of shear band formation. To this end, a new route will be defined for improving the mechanical properties of BMG composites by creating a pattern of multiple embryonic shear bands which subsequently will be confined between precipitates without possibility to mature and propagate. Hence, a quantitative interpretation of the improved ductility will be provided by calculating the critical shear band length and volume and, based on the calculated values, the inclusion architecture will be tailored and the most effective heterostructure in terms of ductility and strength will be constructed.The second goal of the project is to investigate the role of the stress-induced martensitic transformation on the deformation mechanisms of CuZr metallic glass composites reinforced with shape memory phases (B2 CuZr nanoparticles). Along this line, a modelling strategy will be developed to capture and understand the competing deformation mechanism in martensitic nanoparticles and glassy matrix of the composite. Thus, the shear band nucleation induced by the martensitic transformation in crystalline nanoparticles and the shear band intersection with a shape memory inclusion will be investigated. Furthermore, a feasible strategy to control the strain localization by carefully controlling the design parameters, such as nanoparticles volume fraction, distribution, size, number and interdistance, will be provided. This will permit to obtain shear bands with smaller shear offsets and an unfavorable orientation, giving the desirable outcome of more homogeneous deformation. Finally, the transformation induced plasticity in BMG composites will be investigated under iterative deformation. The reversible martensitic transformation is the driving force of the structural rejuvenation in metallic glasses, which subsequently can enhance the ductility and the yield strength of BMG composites.

• DFG Programme: Research Grants
• Cooperation Partners: Professorin Dr.-Ing. Swantje Bargmann; Privatdozent Dr. Celal Soyarslan; Dr. Alexander Stukowski