High-temperature mechanical behavior/microstructure correlation of Cu/Nb nanoscale multilayers

Freestanding Cu/Nb multilayers with 60 nm layer thickness were tested in tension at temperatures ranging from 20 °C to 700 °C at strain rates on the order of 1 × 10^-4 s^-1. At room temperature, the composite exhibited high strength (1.2 GPa) and 5% plastic strain to failure, while at the upper temperature regions tested (700 °C); the composite underwent elongation to 0.3 true strain at a flow stress of 200 MPa. At all temperatures tested, tensile strength of the composite exceeded the rule-of-mixtures estimate by up to an order of magnitude. Additionally, post-mortem cross-sectional transmission electron microscopy analysis of samples taken from both the deformed gage and undeformed shoulder regions show retention of the initial layered morphology. Strengthening mechanisms are discussed in terms of the confined layer slip model, with the trend of decreased strength and increased ductility with increasing temperature attributed to enhanced cross slip and climb of dislocations across interlayer boundaries.