Preparation And Mechanical Properties Of Nanocrystailine Copper

Numerical studies on the measurement of mechanical properties of nanocrystallinemetal have been appeared over past decades. The methods to characterize and measuremechanical properties of the nanocrystalline metal are also emerging in endlessly. Withthe development of synthesis technology on nanocrystalline metal, the grain size,structure, and the purity of material can be controlled and optimized, which provide agood technical support for the research of nanocrystalline metal. Based on thisbackground, we synthesize nanocrystalline copper with different grain size and structurethrough the experiment to study the mechanical properties of nanocrystalline metal andthe deformation mechanism on different conditions, which finally provides theoreticalsupport for the application of nanocrystalline metals. To achieve this goal, our works areas follows:1. Different grain sizes of nanocrystalline copper were synthesized by an improvedelectric magnetron sputtering and brush-plating technique. Experimental materials andequipments were used and experimental parameters were optimized to control the grainsize of nanocrystalline copper. For brush-plating technique, the electric current densityand the ion concentration of copper were controlled to get different grain size anddifferent numbers of twins. As to the method of magnetron sputtering. By changing thesputtering power, sputtering pressure, we can also control the grain size in a smallerrange. The microstructure and the grain size distribution of the samples were detected bytransmission electron microscopy.2. Nanocrystalline copper of the grain sizes of~59nm,~120nm and~200nm wereused to do tensile experiments. Based on the analysis of the stress-strain curve underdifferent strain rate, we can know that the relationship between the elastic, plastic andstrain rate of nanocrystalline copper are obvious. Through the analysis of the morphologyafter the tensile experiments, obvious nest morphology was found on the fracture ofnanocrystalline copper. The morphology of the nest and the fracture ways are closely related to the grain size and strain rate.3. Nanocrystalline copper of the grain size range from about~22nm to~210nmwere studied by load and depth sensing nanoindentation methods with Berkovich tip atthe strain rate of0.004s-1,0.04s-1and0.4s-1. Laser scanning confocal microscope hasbeen used for the imaging of the indent morphology and evaluation of the deformationafter unloading. Three parameters (hb, hiand hd) have been established to illustrate thedegree of residual indent impression influenced by strain rate and grain size. Further, weexplore the relationship between the strain rate, grain size and the morphology afterindentation, which can refer to the practical application of the measurement materialhardness and elastic modulus.4. Creep behavior of nanocrystalline copper with average grain sizes~10nm and~23nm were experimentally characterized using nanoindentation after loading strain raterange from4×10-1s-1to4×10-3s-1. It is found that creep strain and creep strain rate areconsiderably significant for smaller grain sizes at higher loading strain rates. Thepossibility of a dislocation absorption in a smaller grain size at high loading strain ratecan results in a higher density of stored dislocations, which is contributed to thefollowing creep behavior in the holding regime. Comparing the experimental creep strainrate at different given holding time with that predicted by a model, it can be concludedthat the stored dislocations can be absorbed more rapidly in the~10nm copper, inducingthe creep behavior mediated by GB sliding in the initial holding regime and then GBdiffusion in subsequent deformation process. While in the~23nm, the primary creepmechanism is still dislocation activities gradually replaced by the GB sliding in thesubsequent creep process.