Additive Manufacturing of Negative Thermal Expansion Metamaterials Using Steels

Negative thermal expansion (NTE) materials are critical for applications sensitive to thermal expansion, such as precision instrumentation and aerospace systems, but their use is often limited by reliance on rare or expensive materials. Architected NTE metamaterials fabricated from ubiquitous structural alloys like steel present a transformative and scalable alternative. This study focuses on fabricating such metamaterials using laser powder bed fusion (LPBF) of AISI 304L stainless steel and SAE grade 300 maraging steel in bi‐material configurations. Initial efforts optimize LPBF parameters to optimize interfacial strength through detailed process‐structure‐property investigations. Mechanical properties across the interface are characterized using uniaxial tensile testing, nanoindentation, and scratch resistance measurements, while scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), and electron backscatter diffraction (EBSD) are utilized to analyze interfacial microstructure and bonding. Multiple support‐free, thermally responsive bi‐material lattice topologies are computationally designed to ensure manufacturability using LPBF, with their selection informed by finite element simulations. Subsequently, lattices are fabricated using optimized LPBF parameters and experimentally evaluated for their thermal expansion performance using digital image correlation (DIC). All lattice variants demonstrate NTE behaviour, with octagonal and dodecagonal bipyramid configurations achieving the highest magnitudes of negative thermal expansion coefficient.