Development of crystallographic texture during high rate deformation of rolled and hot-pressed beryllium (original) (raw)
Related papers
Role of twinning and slip during compressive deformation of beryllium as a function of strain rate
International Journal of Plasticity, 2012
An experimental and theoretical investigation was carried out to study the strain rate dependent plastic response of beryllium over a wide range of applied compression strain rates, 10 À4-10 4 /s. At each rate, the evolution of flow stress and the final texture with deformation was obtained from a non-textured hot-pressed (HP) sample and a textured rolled sheet. The rolled sheet material was compressed in both the in-plane (IP) and throughthickness (TT) direction for comparison. The twin volume fraction was determined from the change in texture. The activity of twinning was strongly dependent on strain rate in the IP and HP samples. We applied a multi-scale constitutive model for hexagonal close packed polycrystals that accounts for crystallographic slip and twinning on individual systems in each crystal, as well as twin reorientation. Rate effects enter the calculations only through thermally activated dislocation glide on the active slip modes. The importance of this study is that it points to the necessity of using a crystallographic model based on microstructure evolution to understand the role played by plastic anisotropy, slip-slip competition, and slip-twin competition, in the mechanical response of HCP aggregates. The model reproduces the observed flow curves and texture evolution for all tests with a unique single crystal set of parameters.
International Journal of Plasticity, 2013
A polycrystalline material, deformed to large plastic strains and subsequently reloaded along a distinct strain path, exhibits a change in flow stress and hardening behavior. Such changes upon reloading depend on the level of mechanical anisotropy induced by texture and sub-grain microstructure developed during prior loading. In order to comprehend such material behavior, we extend a previously developed rate-and temperature-sensitive hardening law for hexagonal single crystals that accounts explicitly for the evolution of dislocation densities by including the effects of reverse dislocation motion and de-twinning on strain hardening and texture evolution. The law is implemented within a visco-plastic self-consistent polycrystalline model and applied to simulate macroscopic behavior of polycrystalline beryllium during strain-path changes. We show that the model successfully captures the mechanical response and evolution of texture and twin volume fraction during pre-loading in compression and subsequent cross-reloading in compression along two orthogonal directions at two different strain rates. These predictions allow us to elucidate the role played by various slip and twin mechanisms, de-twinning, and reverse dislocation motion on strain hardening and texture evolution of beryllium during strain-path changes. The model is general and can be applied to any metal deforming by slip and twinning.
A neutron diffraction and modeling study of uniaxial deformation in polycrystalline beryllium
Metallurgical and Materials Transactions A, 2003
The deformation of polycrystalline beryllium to strains of 60.8 pct in uniaxial tension and compression was studied by neutron diffraction and modeled using an elasto-plastic self-consistent (EPSC) model. The beryllium response is asymmetric with respect to tension and compression in both the macroscopic behavior, as displayed in the stress/strain curve, and the microscopic lattice response. The EPSC model qualitatively reproduces the lattice strain curves in tension and compression with the assumption of pyramidal slip being active, in addition to prism and basal slip and with the inclusion of thermal residual stresses developed during processing. Although it underpredicts the magnitude of the observed strains, it demonstrates that accounting for residual stresses of thermal origin is crucial for understanding the evolution of lattice strains during uniaxial loading.
Materials Processing and Texture, 2008
Four crystal plasticity codes, the viscoplastic Material Point Simulator (MPS) developed at Cornell and the ViscoPlastic Self-Consistent code (VPSC7b) developed at LANL, and two elastic-viscoplastic codes developed at Drexel University, were employed to calculate deformation textures and mechanical properties of model polycrystalline specimens by simulating isochoric, free upsetting. Uniaxial compression of a model sample with a starting random texture of 5000 grains was carried out at a constant true strain rate of 0.001/s to a true strain of 1.0 with 0.02 strain increments. Material properties simulated a face-centered cubic (FCC) alloy, Type 304 Stainless Steel, and a hexagonal close-packed (HCP) material, unalloyed Ti. Both non-hardening and linear hardening conditions were investigated. Different strain-rate sensitivities simulated deformation conditions appropriate to ambient and elevated temperature conditions. All codes permitted use of the Taylor homogenization hypothesis, resulting in an upper bound for the mechanical properties. All codes produce essentially identical results for the same input material, homogenization hypothesis and deformation conditions. For comparison, one alternative homogenization hypothesis to model grain interactions was examined for each of the MPS and VPSC7b codes.
Peculiarities in the Texture Formation of Intermetallic Compounds Deformed by High Pressure Torsion
MRS Proceedings, 2014
ABSTRACTNiAl, YCu and TiAl polycrystals with B2 and L10 structure, respectively, have been deformed by high pressure torsion (HPT) at temperatures between 20°C and 500°C at a hydrostatic pressure of 8 GPa to high shear strains. Local texture measurements were done by diffraction of high-energy synchrotron radiation and X-ray microdiffraction. In addition, the microstructure was analyzed by electron backscatter diffraction (EBSD). Besides typical shear components an oblique cube component is observed with quite large rotations about the transverse direction. Based on the temperature dependence of this component as well as on microstructure investigations it is concluded that it is formed by discontinuous dynamic recrystallization. The influence of high pressure on recrystallization of intermetallics at low temperatures is discussed.
Acta Materialia, 2012
Different approaches to the modeling of twinning are examined within the framework of a crystal plasticity finite-element code. The model predictions are compared with in situ neutron diffraction experiments previously carried out on zirconium and magnesium alloys. The experiments are used to evaluate different model assumptions regarding the stress state inside newly formed twins at inception, as well as different assumptions concerning the interaction between twin and parent grain during subsequent twin growth. In particular the relaxation in some grain orientations that is experimentally observed, and is associated with twin-induced stress relief, can be captured by the model under appropriate assumptions.