Bi-modal Structure of Copper via Room-Temperature Partial Recrystallization After Cryogenic Dynamic Compression

Pure copper was compressed at high strain rates (over ~3 × 103 s−1) under liquid nitrogen. This deformation resulted in bi-modal microstructures of ultrafine grains and abnormally grown micro grains, and in greater hardness (by ~30 Hv) than room-temperature, dynamically deformed copper. This bi-modal microstructure is attributable to partial recrystallization at room temperature, activated by high-energy states and by twins generated at high Zener–Hollomon parameter conditions. This result demonstrates a new approach for producing bi-modally structured materials.