Growth Twins and Deformation Twins in Metals Beyerlein, Irene J; Zhang, Xinghang; Misra, Amit
Annual review of materials research,
07/2014, Letnik:
44, Številka:
1
Journal Article
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This article reviews recent basic research on two classes of twins: growth twins and deformation twins. We focus primarily on studies that aim to understand, via experiments, modeling, or both, the ...causes and effects of twinning at a fundamental level. We anticipate that, by providing a broad perspective on the latest advances in twinning, this review will help set the stage for designing new metallic materials with unprecedented combinations of mechanical and physical properties.
In this work, we employ the recently developed framework for the explicit modeling of discrete twin lamellae within a three-dimensional (3D) crystal plasticity finite element (CPFE) model to examine ...the effects of dislocation densities in the twin domain on twin thickening. Simulations are carried out for 1¯012101¯1 extension twins in a magnesium AZ31 alloy. The model for the twin lamellae accounts for the crystallographic twin-matrix orientation relationship and characteristic twin shear transformation strain. The calculations for the mechanical fields as a result of twinning consider that one of three types of twin-dislocation density interactions have occurred. One case assumes that the expanding twin retains in its domain the same dislocation density as the parent. The second one considers that twin expansion has lowered the dislocation density as the twin thickens, and the last one, the Basinski effect, assumes that when twin sweeps the region, the dislocation density incorporated in the twin domain is amplified. In the modeling approach, the twin is thickened according to a criterion that maintains the stress state in the vicinity of the grain at a pre-defined characteristic twin resistance. The calculations show that most of the averaged properties, such as the rate of dislocation storage in the entire twin grain, the twin growth rate, the stress field in the twinned grain and neighboring grains, and the slip activity in the parent matrix are not significantly altered by dislocation storage in the twin. The results indicate that, however, the slip activity in the twinned domain is affected. In particular, in the increased dislocation density case, the rate of dislocation density in the twin domain increases at low strains when the twin is first growing from 2% to 5% volume fraction. This initial boost in the dislocation density storage rate causes the newly expanded dislocation twin to contain more stored dislocations than the other cases for all strain levels. Another interesting difference concerns the preference for one or two twins for the same total twin volume fraction; for the increased dislocation twin or twin that retains the dislocation density as it grows, formation of two twins is favored. For a twin that removes dislocation density, only one twin is preferred. The results imply that in the case with reduced dislocation density leads to lower stored dislocations and dislocation storage rates, and lower pyramidal slip activity.
•Effects of dislocation storage in twin domain on twin thickening are studied using CPFE.•Slip activity in twin domain is enhanced by dislocations contained in the twin.•Rate of twin lamella thickening decreases with the rate of stored dislocations in the twin.•Formation of one vs. multiple twin lamellae is influenced by dislocations stored in the twin.
In this work, we describe a finite element (FE) implementation of an elasto-plastic self-consistent (EPSC) polycrystal plasticity model termed FE-EPSC, which is intended for simulations of metal ...forming. To this end, we present an analytical Jacobian, which is necessary for the implicit coupling and ensuring a fast convergence. Every FE integration point is a material point that can be represented either by a single crystal or a polycrystalline material. The constituent crystal can deform by a combination of anisotropic elasticity, crystallographic slip, and deformation twinning. The model is validated and applied to a suite of tests, including monotonic compression, cyclic forward loading, unloading and reverse loading and non-monotonic four-point bending, and materials, such as different alloy compositions, crystal structures, and initial microstructures. The same FE-EPSC framework is applied for all these cases with the main differences pertaining to intrinsic properties, such as the available slip and twinning deformation modes, and the material parameters for activating and hardening of these modes. Full characterization for these parameters for high-purity α-Ti is presented here for the first time. Through these examples we show that, in addition to being predictive with great accuracy, the key advantage of this model lies in its versatility. It accounts for the development of backstress aided dislocation glide, thermally activated storage of dislocations, elastic anisotropy, crystallographic slip and deformation twinning via multiple modes, and de-twinning as well as multi-level homogenizations.
•An elasto-plastic self-consistent crystal plasticity model is embedded in an implicit finite element framework.•A fully analytical Jacobian matrix enabling an efficient coupling and fast convergence is presented.•A single crystal or a polycrystalline material point can be considered at a finite element integration point.•Several validation and application case studies are presented illustrating the versatility of the new model.•The model predicts the evolution of elasto-plastic anisotropy, hardening, unloading, Bauschinger effect, and geometry.
•Texture evolution is analyzed to determine whether pyramidal I or pyramidal II slip activates.•Micromechanics-based EPSC model is used to calculate reorientations in an Mg-4%Li ...alloy.•Single-slip-mode model is developed to identify crystals favoring pyramidal I and II slip.•Simulations and measurements indicate that pyramidal I dominates over pyramidal II slip.•Rolling texture components that distinguish pyramidal I and II slip activity are identified.
Due to the geometry of the hexagonal close-packed (HCP) lattice, there are two types of pyramidal <c+a> slip modes: {101¯1}〈112¯3¯〉 or type I and {1¯1¯22}〈112¯3〉 or type II in HCP crystalline materials. Here we use crystal plasticity to examine the importance of crystallographic slip by pyramidal <c+a> type I and type II on texture evolution. The study is applied to an Mg-4%Li alloy. An elastic-plastic polycrystal model is employed to elucidate the reorientation tendencies of these two slip modes in rolling of a textured polycrystal. Comparisons with experimental texture measurements indicate that both pyramidal I and II type slip were active during rolling deformation, with pyramidal I being the dominant mode. A single-slip-mode analysis is used to identify the orientations that prefer pyramidal I vs. II type slip when acting alone in a crystal. The analysis applies not only to Mg-4%Li, but identifies the key texture components in HCP crystals that would help distinguish the activity of pyramidal <c+a> I from pyramidal <c+a> II slip in rolling deformation.
Bulk nanostructured metals can attribute both exceptional strength and poor thermal stability to high interfacial content, making it a challenge to utilize them in high-temperature environments. Here ...we report that a bulk two-phase bimetal nanocomposite synthesised via severe plastic deformation uniquely possesses simultaneous high-strength and high thermal stability. For a bimetal spacing of 10 nm, this composite achieves an order of magnitude increase in hardness of 4.13 GPa over its constituents and maintains it (4.07 GPa), even after annealing at 500 °C for 1 h. It owes this extraordinary property to an atomically well-ordered bimaterial interface that results from twin-induced crystal reorientation, persists after extreme strains and prevails over the entire bulk. This discovery proves that interfaces can be designed within bulk nanostructured composites to radically outperform previously prepared bulk nanocrystalline materials, with respect to both mechanical and thermal stability.
Particularly in plastically anisotropic crystals, such as hexagonal close packed (HCP) materials, plastic deformation is realized by slip acting in the small volumes within individual crystals. Here ...we extend a full field fast Fourier transform (FFT)-based elasto-viscoplastic formulation to simulate the development of a single slip band on either prismatic or basal planes spanning a crystal. Calculations of the strain and stress fields induced locally within the band and parent crystal, and ahead of the band/grain boundary junction in the neighboring crystal are analyzed as the slip band intensifies under increasing applied strain. We report a substantial influence of the crystallographic orientation of the nearest neighboring grain on the rate of slip band localization. Performing the analysis on two materials, CP-Ti and Mg, indicates that the strength of the material affects the rate of localization, with stronger materials tending to localize more easily. A slip band tip stress-based criterion is proposed for identifying the nearest neighbor orientations in which slip band transmission is possible and the likely slip system for which it occurs. This indicator is validated against experimental studies on commercially pure Ti, an Mg–Y alloy, and Ti–6Al–4V. We show that for low GB misorientations, the slip band is likely to transmit into another slip band of the same type in the neighbor grain, while for high GB misorientations, it is likely to transmit into one of a different type or to not transmit at all.
•An FFT-based elasto-viscoplastic technique is presented to model discrete slip bands.•The model captures shear localization within slip bands with applied strain.•A slip band tip stress-based criterion is proposed to identify slip transmission paths.•Nearest neighbor grain orientation affects slip band development and its potential transmission.•Type of transmitted slip system is correlated with the misorientation between two grains.
An elasto-plastic polycrystal plasticity model is developed and applied to an Inconel 718 (IN718) superalloy that was produced by additive manufacturing (AM). The model takes into account the ...contributions of solid solution, precipitates shearing, and grain size and shape effects into the initial slip resistance. Non-Schmid effects and backstress are also included in the crystal plasticity model for activating slip. The hardening law for the critical resolved shear stress is based on the evolution of dislocation density. Using the same set of material and physical parameters, the model is compared against a suite of compression, tension, and large-strain cyclic mechanical test data applied in different AM build directions. It is demonstrated that the model is capable of predicting the particularities of both monotonic and cyclic deformation to large strains of the alloy, including decreasing hardening rate during monotonic loading, the non-linear unloading upon the load reversal, the Bauschinger effect, the hardening rate change during loading in the reverse direction as well as plastic anisotropy and the concomitant microstructure evolution. It is anticipated that the general model developed here can be applied to other multiphase alloys containing precipitates.
•An elasto-plactic crystal plasticity model is developed for Ni-based superalloys.•The model is dislocation-based accounting for precipitates, non-Schmid effects, and backstress.•The model considers anti-phase boundary energy formed by shearing of precipitates.•The model is used to interpret monotonic and cyclic deformation of Inconel 718.•Hardening, non-linear unloading, Bauschinger effect, anisotropy, and texture are predicted.
In this work, we use crystal plasticity finite element (CPFE) models of 2D and 3D polycrystalline microstructures to elucidate 3D topological effects on microstructural evolution during rolling ...deformation. The important capabilities of our CPFE framework are that it predicts not only texture evolution but also the evolution of intra-grain and inter-grain misorientations, grain shape and grain boundary character distribution. These abilities are possible because both grain structures and grain boundary surfaces are explicitly meshed. Both the 2D and 3D models predict heterogeneous deformation within the grains and across the polycrystal. They also predict similar evolution in grain shape and texture. However, we find that the inter-granular misorientations are higher, the intra-granular misorientations are lower, and the texture evolves faster in 3D compared to 2D, differences which increase with strain level. We attribute these growing differences to the fact that in the 3D microstructure, grains are allowed to reorient both in plane and out of plane to preferred orientations, unlike in 2D. Interestingly, we also find that in the 3D model, the frequency of Σ3 boundaries increases with rolling strain up to the largest strain studied, 1.0. The important 3D effects revealed here can help studies that use CPFE models for understanding microstructural evolution, localization, and damage.
•Evolution of grain and grain boundary structure during plastic deformation is studied using crystal plasticity.•Procedures for creation, meshing and quantitative analysis of grain structure and grain boundaries are developed.•Systematic comparison between predictions on analogous 3D and 2D microstructures is conducted.
This article reviews the growing body of work over the past decade investigating the effect of interface crystallographic character and resulting local interface structure on the mechanical behavior ...in bimetallic nanolayered composites. It has been shown that nanolayered composites exhibit enhanced strength, thermal stability, radiation damage tolerance, and resistance to shock deformation in comparison to their coarse-grained constituents. These unique behaviors are attributable to the high density of interfacial content, as well as the local interface structure and its influence on mechanically or irradiation-induced defects. Here, we cover recent literature on Cu–Nb nanolayered composites synthesized via different pathways including physical vapor deposition and severe plastic deformation techniques such as accumulative roll bonding. By altering the synthesis method, we can produce materials with similar chemical composition and layered morphology, while varying only the crystallographic character of the interface as defined by the orientation relationship and interface plane. This capability, in turn, opens an unprecedented opportunity for systematic investigation of the local interface structure on subsequent behavior, while keeping all other variables constant. We begin with a discussion of interface structures that develop as a function of their processing path. We then follow with the effects of interface structure on dislocation nucleation and deformation twinning. Next, we discuss interface effects on mechanical behavior at quasi-static ambient conditions and later under extreme strains, strain rates, and temperatures. Taken together, these examples provide a strong indication that interface structure matters. The exciting implication is that bimetal interfaces can potentially be engineered for optimal material performance.
A novel interface engineering strategy is proposed to simultaneously achieve superior irradiation tolerance, high strength, and high thermal stability in bulk nanolayered composites of a model ...face‐centered‐cubic (Cu)/body‐centered‐cubic (Nb) system. By synthesizing bulk nanolayered Cu‐Nb composites containing interfaces with controlled sink efficiencies, a novel material is designed in which nearly all irradiation‐induced defects are annihilated.
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