Abstract: Nanoscale metallic multilayers (NMMs) have attracted significant attention owing to their enhanced mechanical properties and excellent thermal stability. However, the underlying deformation mechanisms of the high-temperature annealed microstructures have not been well clarified. In this study, the effect of annealing temperatures (500, 600, 700, 800, and 1000 °C) on the microstructural evolution and mechanical properties of Cu/Nb NMMs was investigated systematically. The results show that when the annealing temperature is lower than 800 °C the Cu/Nb NMMs maintain their initial continuous nanolayered structure. As the annealing temperature reaches 1000 °C, a thermal instability, driven by thermal grain boundary grooving and a Rayleigh instability, leads to the pinching off of the nanolayered structure and even a complete disintegration into an equiaxed grain structure. Uniaxial tensile tests show that 1000 °C annealed samples exhibit an enhanced strain hardening capability compared to as-rolled NMMs and this imparts superior ultimate tensile strength (∼492 MPa) and a high elongation (∼20%). TEM observations demonstrate that high-density entangled dislocations exist in the Cu-Nb interface and layers after tensile testing of the high-temperature annealed samples. The dislocation tangles lead to stable and progressive strain hardening which is the dominant factor in determining the superior combination of strength and ductility of the high-temperature annealed samples. Thus, this study offers a promising strategy for evading the strength-ductility dilemma and instead promotes a more in-depth understanding of the deformation mechanisms of heterostructured materials.

Key words: Annealing, Interfaces, Mechanical properties, Nanoscale metallic multilayers, Thermal stability, Recommended articles