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

摘要

Nanoscale metallic multilayers(NMMs)have attracted significant attention owing to their enhanced me-chanical 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℃)on the microstructural evolution and mechan-ical properties of Cu/Nb NMMs was investigated systematically.The results show that when the anneal-ing temperature is lower than 800℃the Cu/Nb NMMs maintain their initial continuous nanolayered structure.As the annealing temperature reaches 1000℃,a thermal instability,driven by thermal grain boundary grooving and a Rayleigh instability,leads to the pinching offof the nanolayered structure and even a complete disintegration into an equiaxed grain structure.Uniaxial tensile tests show that 1000℃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 progres-sive 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 de-formation mechanisms of heterostructured materials.