Mechanical Behavior And Texture Evolution Of Low Stacking Fault Energy FCC Metals At Large Deformation

The state of grain orientation aggregated distribution in one or more orientation positions in polycrystalline material is called the texture. Texture has an important influence on the mechanical behavior, some physical and chemical properties, as well as it is directly related to the performance in the production and follow-up engineering applications. Therefore, accurate understanding the deformation microscopic mechanism, predicting and controlling the deformation texture has become an important field of development new materials. The micro-indentation hardness testing method, X-ray diffraction, electron backscatter diffraction and neutron diffraction techniques were employed to characterize deformation microstructure and mechanical behavior for face centered cubic metals with different stacking fault energy in this thesis. Based on above-mentioned measurement techniques, combined the calculations of Schmid Factor for{111}<110> slip systems and{111}<112> twin systems, the Taylor Factor in the full-constraints Taylor model, and elastoplastic self-consistent model, by means of fortran77and Matlab programming language to investigate the mechanical behaviors and texture evolution for f.c.c. metals with various stacking fault energy.In this study, using micro-indentation hardness testing method, microhardness testing was carried out within the region with strain marking and the region without strain marking on the different macroscopic sample planes under a variety of thickness reduction for H68single-phase brass. The results show that the microhardness value of the region with strain marking is higher than the region without strain marking about226MPa, and it mainly dues to work hardening caused by twin boundaries impeding dislocation movement. The microhardness value shows an increasing tendency with the increase of the cold rolling reduction in brass, and the generation of shear bands has a softening effect on the matrix.Macro and micro mechanical behaviors of loading and unloading stage under uniaxial tensile state for f.c.c.copper and brass were simulated. The results show that the grain orientation dependent stresses are small for copper and brass at the elastic loading stage. The grain orientation dependent stresses mainly arise because of plastic deformation anisotropy and the stresses are relatively the biggest at the plastic loading stage. The grain orientation dependent stresses still exist at the unloading stage for copper and brass. The linearity of the lattice strain increasing with the macroscopic strain is relatively well for{311} and{111} crystal planes. By analyzing microscopic deformation behavior at different deformation stage, we can get the conclusion that the grain orientation dependent stresses in brass are greater than copper.X-ray diffraction and neutron diffraction techniques were used to characterize the macro texture of the different metals under various thickness reductions. The results show the texture evolution mechanical under large deformation is that copper-oriented grains rotate to the Goss orientation around the<110> crystal direction firstly, then rotate to the Brass orientation around the{110} crystal plane. By analyzing Schmid Factor of slip and twin behaviors and Taylor Factor, we can get the conclusion that twin behavior is the essential of disappearance for Copper oriented grains for low stacking fault energy f.c.c. metals.Micro-orientation and structure were characterized using electron backscatter diffraction technique on the various thickness reductions in single-phase brasses. The result shows that the dislocation slip is main deformation mechanical at the early deformation stage. The twin systems are activated and the shear bands are generated with the increasing thickness reduction. With the increase of deformation, the volume fraction of twin crystal is saturated and gradually reduces, in addition the percent of the shear bands increases until the grains are completely broken.Shear bands are generated in the dense twin-matrix layers and relative big misorientation exists in the internal of the shear bands, the macroscopic appearance of the shear band formation is that the grains shear to each other on twin-matrix layers. The generation of shear bands is the main reason of the enhancement of the Brass oriented grains. The plastic deformation mainly occurs in the shear band regions under large deformation thickness reduction for low stacking fault energy f.c.c. metals, and the deformation mechanicals in the shear bands are still dislocation slip and twining.