In Situ Deformation Technique And Mechanical Propertity Study Of Low Dimentional Nano-Materials

For materials, elasto-plastic deformation is always a hot study topic. Sizeeffect study of the elasto-plastic during the deformation of materials has attracted lostof attention. Transimission electron microscope (TEM) provided chance for us toreveal the straucture envolution information at aomic scale, but due to the lack ofexperimental methods, it is very difficult to do these in-situ experiments, so in the pastyears, researchers have explored the deformation mechanisms of metals mainlythrough conventional postmortem TEM observations, during which the deformationdefects (dislocations, deformation twins, and kinks et al.) remaining in the sample canbe identified and subsequently used as the clues to deduce the possible deformationmechanisms. However, this kind of reasoning unavoidably involves manyassumptions and hypothesis, which need to be proved by the direct experimentalevidences. So it is a challenge job to do the in-situ experiments to obstain structuralevolution information at atomic scale during the deformation process for singlenano-object.In this paper, using several kinds of mechanical testing instruments and methodswith self-property right, systemic study of elasto-plastic deformation mechanisms hasbeen revealed to understand the propertity of metallic materials:1. Based on SEM, TEM and HREM, home-made in situ tensile techeniques havebeen developed for0-D nano-particles,1-D nano-objects,2-D nanofilm,3-D bulkmaterials; an in situ double tilt mechanical and electrical properties integrated testingholder for TEM and a system to study mechanical propertity of materials under anytemperature have been developed. With the techniques based on TEM which alsocontains the double tilt ability, in situ tensile test of amorphous silica glass nanowire,polycrystalline Cu film and single Cu wires cut by FIB has been conducted to studythe structure evolution process of silica glass nanowire and the size effect ofelasto-plastic deformation mechanism of single crystal Cu.2. Tensile test of amorphous silica nanowire has been done in TEM and HREMwith beam off, radial distribution function (RDF) and in situ Raman spectra have beenused to study its deformation process and structural evolution process combined withthe result from MD simulation.3. Three sets of uni-axial tensile tests have been performed in situ inTEM/HREM on Cu nanowires (NWs) to accurately map out the sample sizedependence of elastic strain limit. Atomic-resolution evidence was obtained for an exceedingly large recoverable strain (as much as7.2%) that can be sustained in thelattice of a single-crystalline Cu NW with a diameter of~5.8nm. This ultra-highelastic strain is consistent with the predictions from molecular dynamics simulationsfor nanowires and approaches the ideal elastic limit predicted for Cu by ab initiocalculations.4. In situ tensile tests of Cu single crystals in a high-resolution transmissionelectron microscope reveal a new size-effect of sample dimensions on plasticitymechanisms. When the crystal size was reduced to <~150nm, the normal fulldislocation slip was taken over by partial dislocation mediated plasticity (PDMP). Wedemonstrate this transition in a quantitative manner by assessing the relativecontributions to plastic strain from PDMP, and compare the cross-over sample sizewith model predictions. At the same time, we find that when partial dislocation wasactivated, deformation twin become active and dominate the plastic deformation ofmaterial, more interestingly, with size further reducing, contribution to the plasticdeformation decreased again, a double cross-over was revealed.