Effect of grain orientation and local strains on void growth and coalescence in titanium (original) (raw)
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Three-Dimensional Investigation of Void Growth Leading to Fracture in Commercially Pure Titanium
De Graef/1 st International, 2012
The fracture process of commercially pure titanium was visualized in model materials containing artificial holes. These model materials were fabricated using a femtosecond laser coupled with a diffusion bonding technique to obtain voids in the interior of titanium samples. Changes in voids dimensions during in-situ straining were recorded in three dimensions using x-ray computed tomography. Void growth obtained experimentally was compared with analytical model. The model predicted well void growth. Behavior between voids was justified in terms of grain orientation. Depending on the number of grains between voids and the grains orientation, two types of fracture behaviors were observed: i) brittle fracture when grains were in a hard orientation and when few grains were present between voids; ii) ductile fracture when grains were in a soft orientation and when several grains were present between voids.
Metallurgical and Materials Transactions A, 2011
Using a four-point bend sample of commercial purity titanium deformed to a surface strain around 1.5%, the active dislocation slip and twin systems in a microstructural patch of about 15 grains were quantitatively analyzed by a technique combining atomic force microscopy (AFM), backscattered electron (BSE) imaging, and electron backscattered diffraction (EBSD). Local shear distribution maps derived from z-displacement data measured by AFM were directly compared to results of a crystal plasticity finite element (CPFE) simulation that incorporates a phenomenological model of the deformation processes to evaluate the ability of the CPFE model to match the experimental observations. The CPFE model successfully predicted most types of active dislocation slip systems within the grains at correct magnitudes, but the spatial distribution of strains within grains differed between the measurements and the simulation.
Onset of Void Coalescence during Dynamic Fracture of Ductile Metals
Physical Review Letters, 2004
Molecular dynamics simulations in three-dimensional copper have been performed to quantify the void coalescence process leading to fracture. The correlated growth of the voids during their linking is investigated both in terms of the onset of coalescence and the ensuing dynamical interactions through the rate of reduction of the distance between the voids and the directional growth of the voids. The critical inter-void ligament distance marking the onset of coalescence is shown to be approximately one void radius in both measures.
Computational Materials Science, 2014
A computational model of ultrafine grained (UFG) or nanostructured titanium (Ti), based on a finite element (FE) unit cell model of the material and a dislocation density based model of plastic deformation has been developed. FE simulations of tensile deformation of UFG Ti with different fractions and properties of the grain boundary (GB) phase have been carried out. The effect of different degrees of deviation from the equilibrium state of the grain boundaries (GBs) on the mechanical behaviour of nanostructured Ti have been investigated using the combined composite/dislocation dynamics based model. In particular, the effects of different diffusion coefficients in the GB phase, of a high initial dislocation density in the grain boundaries, as well as of atomic scale precipitates are investigated for affecting the deformation behaviour of UFG or nanostructured Ti.
Void formation, void growth and tensile fracture in Ti6AI4V
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1978
The influence of microstructure on void formation, void growth and tensile fracture was investigated for the Ti-6A1-4V alloy, aged to yield strengths of approximately 110 ksi (758 MN/m2), 130 ksi (896 MN/m2) and 140 ksi (965 MN/m2). Void nucleation occurs at α-aged martensite interfaces for both equiaxed (E) and Widmanstätten plus grain boundary (W + GB)α structures as well as within α particles. Void growth appeared to depend on martensite plate lengths for a given aging treatment for Ea structures, whereas it depended on prior β grain size and grain boundary α thickness for W + GBα structures. Two separate critical crack size-fracture stress (corrected for necking) relationships were found for E and W + GBα structures. The fracture energy for both structures was lower than the corresponding fracture energy previously observed for the Ti-5.25Al-5.5V-0.9Fe-0.5Cu(Ti-5-5) alloy,2 and the lower ductilities of aged Ti-6A1-4V were ascribed to this lower fracture energy.
Scientific reports, 2014
Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are for...
Tensile Deformation Behaviors of Pure Ti with Different Grain Sizes under Wide-Range of Strain Rate
Materials
In this study, pure titanium equivalent to Grade 1 was subjected to tensile tests at strain rates ranging from 10−6 to 100 s−1 to investigate the relationship between its mechanical properties and its twinning and slip. Deformation properties and microstructures of samples having average grain sizes of 210 μm (Ti-210), 30 μm (Ti-30), and 5 μm (Ti-5) were evaluated. With increasing strain rates, the 0.2% proof stress and ultimate tensile strength increased for all samples; the fracture strain increased for Ti-210, decreased for Ti-5, and changed negligibly for Ti-30. Comparing high (100 s−1) and low (10−6 s−1) strain rates, twinning occurred more frequently in Ti-30 and Ti-210 at high strain rates, but the frequency did not change in Ti-5. The frequency of 1st order pyramidal slip tended to be higher in Ti-30 and Ti-5 at low strain rates. The higher ductility exhibited by Ti-210 at high strain rates was attributed to the high frequency of twinning. In contrast, the higher ductility o...
Modelling and Simulation in Materials Science and Engineering, 2021
Ductile metals undergo a considerable amount of plastic deformation before failure. Void nucleation, growth and coalescence is the mechanism of failure in such metals.-titanium alloys are ductile in nature and are widely used for their unique set of properties like specific strength, fracture toughness, corrosion resistance and resistance to fatigue failures. Voids in these alloys were reported to nucleate on the phase boundaries between and phase. Based on the findings of crystal plasticity finite element method (CPFEM) based investigation of the void growth at the interface of and phases [1], [2], a void nucleation, growth, and coalescence model has been formulated. An existing single-phase crystal plasticity theory is extended to incorporate underlying physical mechanisms of deformation and failure in dual phase titanium alloys. Effects of various factors (stress triaxiality, Lode parameter, deformation state (equivalent strain), and phase boundary inclination) on void nucleation, growth and coalescence are used to formulate the constitutive model while their interaction with a conventional crystal plasticity theory is established. An extensive parametric assessment of the model is carried out to quantify and understand the effects of the material parameters on the overall material response. Performance of the proposed model is then assessed and verified by comparing the results of the proposed model with the RVE study results. Application of the constitutive model for utilisation in the design and optimisation of the forming process of-titanium alloy components is also demonstrated using experimental data.
Characterization and analysis of deformation heterogeneities in commercial purity titanium
Materials Characterization, 2015
The effects of solute oxygen, loading direction and strain level on the microscale plastic strain distribution in representative areas of commercially-pure titanium have been characterized by correlation of high resolution SEM images captured during in situ tensile tests. A spatial organization of highly-deformed bands was observed from the early stages of plastic flow and remained nearly unchanged as the materials were strained. The high strains close to grain boundaries were related to intense local slip activity, grain boundary sliding or kink bands formation. The plastic strain field was more homogeneous in the oxygen-rich material, which was attributed primarily to a smaller contribution of grain boundary sliding, due to the presence of hard phase particles along the grain boundaries.