The thermal instability mechanism and annealed deformation behavior of Cu/Nb nanolaminate composites

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 (50 0, 60 0, 70 0, 80 0, and 10 0 0 degrees 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 degrees C the Cu/Nb NMMs maintain their initial continuous nanolayered structure. As the annealing temperature reaches 10 0 0 degrees 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 10 0 0 degrees 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.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

The microstructural evolution and mechanical properties of Cu/Nb NMMs under different annealing temperatures were investigated. The results showed that the nanolayered structure of the NMMs is maintained at temperatures below 800°C, but thermal instability occurs at 1000°C, leading to the disintegration of the nanolayered structure. Tensile tests revealed enhanced strain hardening and improved ultimate tensile strength and elongation in the 1000°C annealed samples.