Mechanistic Understanding of Deformation Accommodation and Phase Interaction Governing Ductility and Strain Hardening in Bulk Metallic Glass Composites

Bulk metallic glasses (BMGs) are a unique class of alloys with an amorphous atomic structure that lack long-range crystallographic order. As a result, they exhibit exceptional mechanical properties, including high strength, a large elastic limit, and outstanding corrosion and wear resistance, making them attractive candidates for advanced structural applications. However, their widespread use has been limited by catastrophic failure associated with highly localized deformation and limited macroscopic plasticity at room temperature. A promising strategy to overcome this limitation is to incorporate ductile crystalline phases into the glassy matrix, producing composites that combine high strength with improved damage tolerance. Although bulk metallic glass composites have demonstrated significant improvements in ductility and toughness, the fundamental mechanisms governing deformation partitioning and mechanical interactions between the amorphous and crystalline phases remain poorly understood. This project will address this critical knowledge gap by combining advanced multiscale mechanical testing with state-of-the-art microscopy to quantitatively reveal how individual phases accommodate deformation and interact during loading. The project will provide undergraduate and graduate students with hands-on training in advanced small-scale mechanical testing and materials characterization. Outreach activities with local K–12 schools will engage students through interactive demonstrations and educational programs designed to stimulate interest in mechanics of materials and encourage future participation in STEM fields. This research focuses on CuZr-based bulk metallic glass composites containing a crystalline B2 CuZr phase, which exhibit an exceptional combination of ductility and strain hardening. Despite their outstanding mechanical performance, the mechanisms governing deformation partitioning between the amorphous matrix and crystalline phase throughout deformation remain unresolved, limiting the development of predictive design strategies for high-performance metallic glass composites. This project aims to quantitatively determine how each constituent phase accommodates deformation and how their interactions give rise to enhanced ductility and strain hardening. To accomplish this objective, advanced in situ mechanical testing and state-of-the-art microstructural characterization will be integrated across multiple length scales. Bulk tensile testing, in situ microscale tensile testing, and four-dimensional scanning transmission electron microscopy (4D-STEM) will be combined to establish quantitative relationships among macroscopic deformation, local strain partitioning between the amorphous and crystalline phases, and the evolution of flow defects during deformation. Complementary nanoindentation and in situ micro-tensile experiments will further quantify the mechanical interactions between the constituent phases. This work will provide the first comprehensive, quantitative experimental characterization of phase-specific deformation mechanisms spanning macroscopic, sub-micrometer, and nanometer length scales. The resulting mechanistic understanding will establish fundamental design principles for developing next-generation self-toughening metallic glass composites with enhanced ductility, strain hardening, and structural reliability. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.