Metallic Glasses: Status and Prospects for Aerospace Applications

This Defense Intelligence Reference Document, produced under the Advanced Aerospace Weapon System Applications (AAWSA) Program in 2009, provides a technical assessment of metallic glasses and their potential utility in aerospace structural applications. The document outlines the fundamental atomic structure of metallic glasses, noting that their amorphous nature—lacking the long-range order of crystalline metals—results in unique mechanical properties. While these materials exhibit high strength and stiffness, they are characterized by near-zero tensile ductility and poor fatigue resistance due to the absence of crystalline defects like dislocations, which typically facilitate strain hardening. The report details the processing advantages of metallic glasses, specifically their ability to be formed like thermoplastic polymers near the glass transition temperature, allowing for complex geometries and nanoscale features. However, significant limitations exist, including a lack of suitable lightweight glass-forming alloys, particularly aluminum-rich compositions, and the tendency for brittle fracture. The document emphasizes that metallic glass matrix composites, which incorporate ductile crystalline dendrites, offer a path toward overcoming these limitations by improving fracture toughness and fatigue resistance. The report concludes that while metallic glasses and their composites are likely to see increasing acceptance as structural materials over the next 20 to 50 years, their widespread use in aerospace depends critically on the development of new, lightweight alloys and a deeper understanding of their mechanical behavior and processing requirements.