Fabrication And Properties Of Cu/M(M=Fe,V) Nanomultilayer Materials

Nanomultilayer materials,as a novel nanostructured materials,have many remarkable performance,such as high hardness and strength,outstanding thermal stability and irradiation tolerance,due to its unique composition and microstructure.Thus,it is expected to be extensively used in aerospace,microelectronmechanical system,energy and other fields,especially in the field of next generation energy,nanomultilayer materials are regarded as one of the important candidate structural materials for the construction of advanced fusion reactors in the future.In the design and preparation of high performance materials,interface engineering design is a significant strategy to develop structural materials with good mechanical properties and irradiation resistance.However,traditional preparation technique such as magnetron sputtering technology cannot prepare bulk nanomultilayer materials,which largely restricts the practical engineering application of nanomultilayer materials.Therefore,in this paper,bulk Cu/Fe and Cu/V nanomultilayer materials with high strength and good thermal stability were prepared via cross accumulative roll bonding(CARB)process combined with appropriate intermediate annealing treatment,and their mechanical properties,thermal stability and irradiation resistance were studied.Bulk Cu/Fe and Cu/V nanomultilayer materials with various layer thickness range from micrometer-scale to nanoscale were fabricated via CARB process,and the minimum individual layer thicknesses of Cu/Fe and Cu/V nanomultilayer materials can be up to 30 nm and 20 nm,respectively.Microstructure analysis show that bulk Cu/Fe and Cu/V nanomultilayer materials have achcieved good interface bonding at both the micrometer-scale and nanoscale.For samples of different layer thickness,the Cu/Fe and Cu/V interfaces were relatively sharp and flat,and the intact layered structure was maintained.Furthermore,the high-resolution TEM results of interface show that not only sharp interfaces are observed at the phase interface,but also a lot of fuzzy interfacial structures are observed,that is,interfacial transition zones.The formation of these interfacial transition zones is due to the mixing of immiscible elements caused by the severe plastic deformation during the rolling process.In terms of mechanical properties,Cu/Fe and Cu/V nanomultilayer materials exhibit high strength and hardness,and there is an obvious scale effect between mechanical properties and layer thickness,that is,the strength and hardness increase with the decrease of layer thickness.For the minimum individual layer thickness,the strength and hardness of Cu/Fe and Cu/V nanomultilayer materials are much higher than that of the initial materials.The strengthening behavior of nanomultilayer materials can be explained by the perspective of phase interface strengthening.In terms of thermal stability,Cu/Fe and Cu/V nanomultilayer materials can basically maintain their original mechanical properties after annealing at 500? for 1 hour,indicating that these materials have good thermal stability.The microstructure analysis shows that the microstructure stability of the high-density phase interface in the nanomultilayer materials at high temperature is the root of its good thermal stability.Although good thermal stability is achieved in nanomultilayer materials,the thermally induced microstructural instability is distinct when annealing temperature continues to increase.The grain boundary grooving mechanism is responsible for the distinct thermal instability after high annealing temperature.In addition,obvious annealing induced strengthening behavior was observed in Cu/Fe nanomultilayer materials as annealing temperature rises up to 400?,which is considered to be closely related to the relaxation of interfacial transition zones.Finally,the helium ions irradiation response characteristics and mechanism of 90 nm Cu/Fe and 40 nm Cu/V nanomultilayer materials at different temperatures were studied.After irradiation with fluence of 5 × 1016 ions/cm2 at 500?,some columnar cavities with a large aspect ratio appear at Cu/Fe interfaces,demonstrating that void elongation in the normal direction of the interface requires to satisfy both kinetic(along vacancy flux)and thermodynamic(along {111} plane)factors.In addition,after irradiation with fluence of 1×1017 ions/cm2 at 500? more defects prefer to aggregate at Cu-Cu boundary due to the larger vacancy flux towards to the central boundary from adjacent Cu layers at high temperature,because the V layer pinch-off promote the connection of Cu alternant layers.By contrast,less vacancies from V layer migrating to Cu-V interfaces leads to small cavities.