An X-Ray Diffraction Study Of Confined Deformation Behaviors In Metallic Materials

Metallic materials exhibits extraordinary mechanical behavior owing to the confined deformation from surrounding grains, substrate and interface. Confined deformation existed widely in micro-/nano-electromechanical system(MEMS/NEMS) and some surface mechanical treatment for advanced structure components. Metallic multilayered films are important structure components for electronic devices and interconnects in MENS/NEMS. Metallic multilayered films behave elastic and plastic deformation due to the length scale and interface effects. The deformation mechanisms and mechanical properties of the structure components will influence the working property of the whole system. Laser shock peening(LSP) is widely accepted as the surface mechanical processing in aeroengine blades because of its bigger and deeper residual stress influenced region. Confined deformation is also exist in the LSP process. The distribution of residual stress will affects the lifetime and in-service safety of components. In this thesis, two kinds of system, Cu/Ag and Cu/Cr multilayer films and LSP titanium alloy, have been carefully investigated to reveal the microstructure evolution, micromechanical behavior and deformation mechanism during confined deformation.Two kinds of metallic multilayered films, s-Cu and s-Ag, have been carefully investigated using synchrotron X-ray diffraction(XRD) during the tensile deformations. The stress partitioning behavior was first observed in the metallic multilayered films between sublayers,and quantified by hooke’s law and the model of double phases mixture. The Cu sublayers, working as hard phase in the multilayers, sustained bigger load. The deformation regimes of metallic multilayered films could divided into three parts: I, elastic regime, where only elastic deformation occured in both Cu and Ag sublayers, no layer to layer interaction; II, elastoplastic regime, the soft Ag sublayers began to yield compared to the elastic deformation in Cu sublayers, layer to layer interaction emerged and the interface stress increased quickly with the continued deformation; III, stable plastic regime, Cu sublayers yielded finally, a stable plastic deformation would be reached between the alternating Ag and Cu sublayers, the layer to layer interaction would become stable, and a stable interface stress reached. It was also found in the current investigation that the interface stress could decrease the ductility of the metallic multilayered films.Peak width study has been carefully investigated for different structured Cu/Cr multilayered films using lab XRD during tensile deformation. Reversible peak broadening, which usually observed in nanostructured bulk materials during loading and unloading, was first observed in metallic multilayered films. Dislocation density increased with the increase of strain, and no dislocation network left after unloading. The rate of disolation proliferation was not affected by the thickness of Cu layer. Dislocation tolerance was thickness dependent, more dislocations could be held for thicker Cu layer. Cu/Cr interfaces acted as main source and sink for dislocations.Lattice strain of Cu sublayers in Cu/Cr multilayered films has been carefully investigated using lab XRD during tensile deformation. Length scale(sublayer thickness) and interface effects on mechanical behavior of Cu sublayer are analyzed. The results showed that the ductility and yield strength are length scale and interface dependent. With the decrease of Cu sublayer thickness, the ductility of the Cu sublayer decreased, and the yield strength increased. And due to the interface effect, the ductility of Cu sublayers in Cu/Cr multilayered film was lower than that in single Cu film with same thickness, and the yield strength of Cu wass larger in multilayered film. The yield strengths calculated from Hall-Petch model and confined layer slip model were consistent with experimental values. Metallic multilayered films with higher strength and better ductility could be achieved by modulating sublayer thickness and adjusting interface structures.Residual lattice strains of TC11 titanium alloy with 50% overlapping rate were carefully investigated in through-LSP-treatment direction(treatment surface normal direction) by synchrotron high energy X-ray diffraction after LSP. Both intergranular and interphase stress existed in the LSP sample at either one-shock region or two-shock(overlapping) region. The residual lattice strains in TC11 Titanium alloy were phase and grain-orientation dependent, showing strong strain anisotropy. The residual lattice strains were negative value(compressive state) at surface and near surface, then changed to positive value(tensile state) with depth increase, and then back to initial sample value(very small value, close to 0). Zero lattice strain located at different depths for different hkl reflections. The depth of compressive residual lattice strains for two-shock region was bigger than one-shock region. The “Residual stress hole” was grain-orientation dependent at surface. This evolution of residual lattice strains(?) could be explained by a balance between the residual lattice strain(?)without restriction and the residual lattice strain( ?) with restriction from surrounding grains after shock wave.