Activation Of Different Slip Systems Research Articles

Crystal plasticity analysis of tensile plastic behavior and damage mechanisms of additive manufactured TiAl alloy under elevated temperatures

A crystal plasticity model based on Electron Backscatter Diffraction (EBSD) experimental data has been developed to simulate the tensile behavior of additively manufactured TiAl alloys at various temperatures. To accurately capture the activity of different slip systems and their contribution to the material's plasticity, multiple slip systems across different phases are considered. The validity of the model is verified by comparing the simulation results, such as microscopic properties, with experimental and test data. Additionally, a continuous damage model is incorporated to analyze the damage behavior of additively manufactured TiAl alloys at different temperatures. Compared to experimental data, the crystal plasticity model incorporating damage effectively simulates the tensile failure behavior of TiAl alloys across a range of temperatures.

Influence of pre-rolling deformation on distribution characteristics of T1 precipitate in artificially aged Al–Cu–Li alloy

The predeformation prior to artificial aging plays an important role in enhancing the properties of Al–Cu–Li based alloys. This study focused on investigating the impact of a large amount of prerolling (20%) on the orientation variation and distribution characteristics of T1 precipitates in a rolled Al–Cu–Li alloy. The results revealed that T1 phases precipitated in the same orientation were not strictly parallel within a grain, a small angle existed between different phases in the same direction due to the orientation fluctuation of the matrix induced by prerolling. The misorientation degree of the T1 precipitates presented a slight expend tendency with increasing the aging time. Furthermore, the connection between this orientation distortion of the T1 phases and the tensile properties was discussed. Additionally, it was found that the T1 variants along different orientations were heterogeneously distributed, possibly due to the activation of different slip systems during the prerolling process and the variation in the number of nucleation sites among the nonparallel habit planes.

Grain size and orientation affected deformation inhomogeneity and local damage of hot-deformed Al-Zn-Mg alloy

The forming defects at elevated temperature caused by the microstructural evolution such as grain size, crystal orientations are the critical issue that induced deformation inhomogeneity and local damage which severely limits the application of Al-Zn-Mg alloys in thin-walled structure manufacturing. In this study, the hot deformation behavior and microstructural evolution were investigated via hot stretching tests, electron backscatter diffraction (EBSD) and the transmission electron microscopy (TEM) characterization. Then, an integrated multiscale constitutive model coupled dislocation density based crystal plasticity (CP) model and phase field method (PFM) was established through the reconstructed configuration of deformation gradient emphasized on a damaged part. The coupled CP-PFM model was numerically implemented into Düsseldorf Advanced Material Simulation Kit (DAMASK) software. Subsequently, a set of virtual polycrystalline RVE models assigned with different average grain sizes and two types of RVE models with realistic crystal orientations were constructed from EBSD data. The experimental and simulation results of the Al-Zn-Mg alloy under hot tensile loading showed that the grain size refinement leads to the increase of grain boundary density, which leads to the rapid increase of dislocation density, uniform damage distribution and better work hardening ability. In addition, the coordination of the activation of different slip systems between adjacent grains will lead to the uneven distribution of dislocation density and local damage.

The effect of electric current on dislocation activity in pure aluminum: A 3D discrete dislocation dynamics study

Introducing electric current into metals and alloys to improve their ductility and to reduce the hardening tendency has been widely adopted. Nevertheless, how the electricity affects the plastic deformation of those materials remains a critical issue with controversial opinions. To clarify the material plastic deformation subjected to electric current, or the so-called electroplastic behavior, an in-depth understanding of the dislocation evolution during that process is vital. From that motivation, three-dimensional dislocation dynamics simulations were carried out to explore the dislocation behavior during the uniaxial tensile deformation of pure aluminum with the introduction of electric current. The scattering process between electrons and dislocations was first captured by a physical model. The electron wind force and local heat effect were quantitatively analyzed by figuring out the momentum and the energy transferred during the interaction of electrons and dislocations respectively. The dislocation density evolution, the activation of different slip systems and the dislocation distribution were further analyzed based on the simulations. The dislocation density in the [111] direction is revealed to increase more significantly than [101] and [001] directions with the introduction of electric current. The results show that the current can reduce the flow stress by promoting the activation of the difficult-to-move dislocations. The activation effect reduces the dislocation tangling tendency and leads to more uniform dislocation distribution. Therefore, a reduction of the flow stress can be observed in EAT comparing to TAT, via the discrete dislocation dynamics simulations even though the dislocation densities are similar. The simulation results are also confirmed by the EAT and TAT experiment results and TEM observations.

Dependence of micromechanical behaviours on grain orientation and size in a nanoscale C11b precipitate-strengthened Ni-23Cr-16Mo pillar via micro-pillar compression

Long-range order (LRO) precipitate-strengthening is an important strategy that endows a superior strength-ductility combination in Ni-based alloys. However, the micromechanical behaviour of the LRO phase-strengthened single-crystals and its dependence on size and orientation remain unclear. In this study, the micromechanical behaviour of LRO-C11b phase-strengthened Ni-Cr-Mo pillars was investigated as a function of the pillar's size and orientation. The stress-strain (σ-ε) curve feature in the [20 2 9]-oriented pillars is independent of their sizes, but the yield strength monotonically decreases with increasing pillar sizes due to the size effect. In contrast, the σ-ε curve exhibits quite diversity when the [20 2 9]-oriented pillar is replaced by other oriented pillars. Slip is responsible for the plastic deformation in all [20 2 9]-oriented pillars, regardless of the pillar's size, while the deformation modes exhibit diversity with the change of orientation of the pillars, i.e., slip combined with twinning in the [411]-oriented pillar, twinning in the [001]-oriented pillar, and initial twinning followed by multiple slips in the [111]-oriented pillar. The diversity of deformation modes is related to the activation of different slip systems. (1—11)[110] slip is predominantly activated in the [20 2 9]- and [411]-oriented pillars, while (—111)[110] is activated in the [001]-oriented pillar, and both (1—11)[110] and (—111)[110] are activated simultaneously for the [111]-oriented pillar. After deformation, multiple substructures appear in the post-deformed pillars, including shearing of LRO-C11b by slip bands or deformation twins, double twinning of both C11b precipitates and disordered γ phases, and disordering transformation.

The Outstanding Contribution of Basal Slip in Substructure Development during Friction Stir Processing of Magnesium Alloys

This research reveals the critical role of basal slip in the substructure development during friction stir processing of a magnesium alloy. In this respect, the intragranular lattice rotation axes are considered to identify the activity of different slip systems. The applied shear strain during the procedure is stored in the matrix through slip‐induced rotations at the grain level. The rotations around distinct Taylor axes produce “slip domains” separated by necessary boundaries from the parent grains, significantly contributing in grain refinement. The basal slip is easily activated in grains holding different stored energy; however, the nonbasal slip has a higher dependency on the amount of local applied strain. Determining the contribution of different slip systems in strain accommodation reveals that the basal slip imposes the highest fraction of low‐angle boundaries into the microstructure leading to the development of the ultimate grain boundary structure.

Revealing hot deformation behavior and optimizing process parameters of as-cast Ti–5Al–5Mo–5V–1Cr–1Fe alloy

Hot compression tests are carried out at temperatures ranging from 900 °C to 1050 °C, strain rates ranging from 0.001s−1 to 1s−1 and deformation degree ranging from 60% to 70% on the Gleeble-3500 thermal simulator. Strain-compensated Arrhenius constitutive model, activation energy maps, hot processing maps and microstructure evolution are used to analyse the flow behavior of as-cast Ti-55511 alloy. At low temperature (≤950 °C), the flow softening behavior is mainly related to cracks, deformation bands (DBs) and DRV at high temperature (≥1000 °C) and high strain rate (≥0.1s−1), and DRV at high temperature (≥1000 °C) and low strain rate (≤0.01s−1). DBs and cracks are the main forms of hot deformation instability. There is a competitive relationship between DRV and DBs. Under high strain rate (≥0.1s−1), DBs are more likely to occur. Under low strain rate (<0.1s−1), the DBs are restrained by DRV. The simultaneous activation of different slip systems causes the rotation of different areas in the grains to form DBs. The DRX grains in the DBs are produced by continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX), but the DRX grains in the sample without DBs are produced by CDRX. The analysis of hot activation energy (Q), strain rate sensitivity index (m), power dissipation efficiency (η), flow instability parameter (ξ(ε˙)) and microstructure analysis showed that 1000°C–1050 °C/0.001s−1–0.01s−1 are an optional processing window. And the proportion of recrystallization is the highest at strain of 1.2 and 1000 °C/0.01s−1, so it can be considered as the optimal processing parameter.

Effect of loading orientation on plasticity in nano-laminated CoNiCrFeMn dual-phase high-entropy alloy: a molecular dynamics study

Dual-phase high-entropy alloys (DP-HEAs) have been proved to be a kind of promising materials that exhibit a combination of excellent strength and ductility. Previous studies have emphasized the effect of interface and phase volume fraction on mechanical performance in DP-HEAs. However, the deformation mechanisms such as interplays between dislocations and the constituent phases have not been fully understood. Particularly, the research concerning plastic anisotropy in DP-HEAs is still lacking. Here, molecular dynamics simulations are performed to probe the effect of loading orientation on plasticity in the nano-laminated face-centered cubic (FCC)/hexagonal close-packed (HCP) CoNiCrFeMn DP-HEA. Results reveal that a switch from strengthening to softening and back to strengthening is closely related to the activation of different slip systems when tailoring the inclination angles of the nanolaminates with respect to the tensile direction from 0° to 90°. Slip transfer across phase boundaries, phase transformation and the nucleation of shear bands dominate the plasticity in the samples with low, medium and high inclination angles, respectively. Furthermore, the evolution of microstructures, such as dislocations, stacking faults, and FCC/HCP phase are analyzed to study the underlying deformation mechanisms. These results can help understand the plastic anisotropy of DP-HEAs and design alloys with excellent mechanical properties for engineering applications.

A multiscale computational framework for wear prediction in knee replacement implants

Wear damage represents a long-term material failure that affects the service life of joint implants. Prediction of wear in bearing inserts under arbitrary joint kinematics and kinetics holds an important key to improving the performance of entire joint implant device through new material development and customized geometry design. In this work, a hierarchical multiscale computational framework that predicts the wear rate of ultra-high molecular weight polyethylene (UHMWPE) insert by resolving the microstructure details and microscale deformation mechanisms is developed. A fully dynamic finite element simulation is carried out at the macroscale level to reproduce the interactions between femoral component and UHMWPE insert according to the knee simulator input profiles. The stress evolution history from the initial wear site is extracted and applied back to the representative volume element (RVE) to further study the microscale deformation mechanisms that are related to wear damage. Activation of different slip systems in the crystalline phase as well as the interplay between the crystalline phase and amorphous phase are captured through a semi-crystal plasticity model. Results shown that improving wear resistance requires minimizing the plastic deformation upon the same external loading while maintaining a load-sharing balance between the crystalline phase and the amorphous phase. A combination of high crystallinity, well-dispersed crystallite with small size and texture alignment along the axial load direction can promote activation of chain pull slip that leads to improved wear resistance.

Elevated-Temperature Tensile Properties of Low-Temperature HIP-Treated EBM-Built Ti-6Al-4V.

Evaluation of the high-temperature tensile properties of Ti-6Al-4V manufactured by electron beam melting (EBM) and subjected to a low-temperature hot isostatic pressing (HIP) treatment (800 °C) was performed in this study. The high-temperature tensile properties of as-built and standard HIP-treated (920 °C) materials were studied for comparison. Metallurgical characterization of the as-built, HIP-treated materials was carried out to understand the effect of temperature on the microstructure. As the HIP treatments were performed below the β-transus temperature (995 °C for Ti-6Al-4V), no significant difference was observed in β grain width between the as-built and HIP-treated samples. The standard HIP-treated material measured about 1.4×–1.7× wider α laths than those in the modified HIP (low-temperature HIP)-treated and as-built samples. The standard HIP-treated material showed about a 10–14% lower yield strength than other tested materials. At 350 °C, the yield strength decreased to about 65% compared to the room-temperature strength for all tested specimens. An increase in ductility was observed at 150 °C compared to that at room temperature, but the values decreased between 150 and 350 °C because of the activation of different slip systems.

Numerical modelling of size effects in micro-cutting of f.c.c. single crystal: Influence of strain gradients

A size effect is exhibited by metals in cutting processes at small scales: a nonlinear escalation in the cutting energy per unit volume with a decrease in the thickness of the uncut chip. To understand this phenomenon, a numerical model of orthogonal micro-cutting of f.c.c. single-crystal copper was developed, and three different depths of cut (0.8 μm, 1.4 μm and 2.0 μm) were considered. Enhanced models of crystal plasticity (EMCP) and strain-gradient crystal plasticity (EMSGCP) implemented in ABAQUS/Explicit through a VUMAT Fortran subroutine were used. Obtained results were compared with the experiments reported in the literature. The influence of size effect on deformation response of a single-crystal material was investigated extensively in terms of the distribution of field variables such as strain gradients, stresses, lattice rotations and activity of different slip systems. The influence of crystallographic orientation was also studied. It was observed that the size-effect phenomenon was predicted more accurately with the EMSGCP theory, where polar dislocations evolving during deformation were found to affect it significantly.

Plastic deformation of the CaMg2 C14-Laves phase from 50 - 250°C

Intermetallic phases can significantly improve the creep resistance of magnesium alloys, extending their use to higher temperatures. However, little is known about the deformation behaviour of these phases at application temperatures, which are commonly below their macroscopic brittle-to-ductile-transition temperature. In this study, we therefore investigate the activation of different slip systems of the CaMg2 phase and the occurrence of serrated yielding in the temperature range from 50°C to 250°C. A decreasing amount of serrated flow with increasing temperature suggests that solute atoms govern the flow behaviour when the CaMg2 phase is off-stoichiometric.

In-situ study on tensile deformation and damage evolution of metastable β titanium alloy with lamellar microstructure

Tensile deformation and damage evolution of a metastable β titanium alloy (Ti–5Cr–4Al–4Zr–3Mo–2W–0.8Fe) with lamellar microstructure are studied by in-situ tensile test under scanning electron microscopy. In the tensile process, the main deformation modes include the dislocation slip, phase interface shear and grain boundary shear, and the geometrical orientation of α lamellae determines the activation of different slip systems and whether the interface shear is involved in deformation. The α lamellae may kink and even fragment under severe deformation. Slip transfer is prone to occur between α lamella and β interlayer that satisfy the Burgers orientation relationship, and the slip lines will deflect and bifurcate as more slip systems are activated and grains rotate. Due to the localized stress concentration and inhomogeneous deformation, the grain boundaries, phase interfaces, tips of β interlayers, junctions of colonies composed of α lamellae and shear bands are all the positions where are easy to generate microvoids. The crack propagates along a zigzag path on account of the synergistic reaction mechanism of critical resolved shear stress, activated slip system, shear band and grain boundary shear, resulting in an intergranular and transgranular mixed fracture mode.

Deformation mechanisms of Mg-Ca-Zn alloys studied by means of micropillar compression tests

The effect of Ca and Zn in solid solution on the critical resolved shear stress (CRSS) of <a> basal slip, tensile twinning and <c+a> pyramidal slip in Mg alloys has been measured through compression tests on single crystal micropillars with different orientations. The solute atoms increased the CRSS for basal slip to ~ 13.5 MPa, while the CRSS for pyramidal slip was lower than 85 MPa, reducing significantly the plastic anisotropy in comparison with pure Mg. Moreover, the CRSSs for twin nucleation and growth were very similar (~ 37 MPa) and the large value of the CRSS for twin growth hindered the growth of twins during thermo-mechanical processing. Finally, evidence of <a> prismatic slip and cross-slip between basal and prismatic dislocations was found. It is concluded that the reduction of plastic anisotropy, the activation of different slip systems and cross-slip and the weak basal texture promoted by the large CRSS for twin growth are responsible for the improved ductility and formability of Mg-Ca-Zn alloys.

On the evolving nature of c/a ratio in a hexagonal close-packed epsilon martensite phase in transformative high entropy alloys

Activation of different slip systems in hexagonal close packed (h.c.p.) metals depends primarily on the c/a ratio, which is an intrinsic property that can be altered through alloying addition. In conventional h.c.p. alloys where there is no diffusion-less phase transformation and associated transformation volume change with deformation, the c/a ratio remains constant during deformation. In the present study, c/a ratio and transformation volume change of h.c.p. epsilon martensite phase in transformative high entropy alloys (HEAs) were quantified as functions of alloy chemistry, friction stir processing and tensile deformation. The study revealed that while intrinsic c/a is dependent on alloying elements, c/a of epsilon in transformative HEAs changes with processing and deformation. This is attributed to transformation volume change induced dependence of h.c.p. lattice parameters on microstructure and stress state. Lower than ideal c/a ratio promotes non-basal pyramidal 〈c + a〉 slip and deformation twinning in epsilon phase of transformative HEAs. Also, a unique twin-bridging mechanism was observed, which provided experimental evidence supporting existing theoretical predictions; i.e., geometrical factors combined with grain orientation, c/a ratio and plastic deformation can result in characteristic twin boundary inclination at 45–50°.

Structure Determination of Er Doped Ti-Al-Nb Alloy by Neutron Diffraction Analysis.

Neutron diffraction experiments with both conventional powder diffraction setup and under in-situ compressive loading were conducted to investigate the structural origins of large strength and toughness enhancements in Ti-16Al-27Nb alloy after Er addition. The primary phase is determined to be the ordered B2 structure form, in agreement with the previous electron microscopy study. Lattice strains of {210} and {100} planes were measured as a function of applied stress, and elastic anisotropy was found for both, and strong plastic nonlinearity was discovered for (210) reflection. The grain refinement during plastic deformation was proposed by both the 2D diffraction intensity distribution and SEM observations, while stress-induced martensitic phase transition was not observed in this study. It is believed that the activation of different slip systems and grain refinement might be the structural origin of the novel mechanical properties of this alloy.

In-situ EBSD study of deformation behaviour of 600 MPa grade dual phase steel during uniaxial tensile tests

This paper studied the plastic deformation behaviour of DP600 steel subjected to uniaxial tension, by means of in-situ EBSD technique. It provides experimental evidences and detailed insight into the microstructural aspects of plastic deformation. A phase identification method based on the band slope map of EBSD was adopted to differentiate martensite from ferrite. The results show that the plastic strain localization lies mainly in the ferrite grains, fracture could usually start in ferrite grains close to hard martensite grains. With the increase of strain, average misorientation angle decreased while the fraction of LAGBs increased. Average Taylor factor for the whole microstructure became higher at high strains due to work hardening process, and plastic deformation results in soft regions with zonal distribution parallel to the loading direction. In the undeformed state, the texture orientation (111)[01¯1] and (111)[11¯0] are the major components of the γ-fibre while (223)[11¯0] and (221)[11¯0] are the main components of α-fibre. The intensity of the α-fibre slightly decreased, while the intensity of the γ-fibre increased with increasing strain. Plastic deformation occurred in some grains which were subdivided into different regions due to the activation of different slip systems. The tensile axis orientation of the grain rotated gradually to the line link <100>−<101>, and lattice rotation within one single grain differs from regions to regions.

Analysis of crystallographic preferred orientations of experimentally deformed Black Hills Quartzite

Abstract. The crystallographic preferred orientations (textures) of three samples of Black Hills Quartzite (BHQ) deformed experimentally in the dislocation creep regimes 1, 2 and 3 (according to Hirth and Tullis, 1992) have been analyzed using electron backscatter diffraction (EBSD). All samples were deformed to relatively high strain at temperatures of 850 to 915 °C and are almost completely dynamically recrystallized. A texture transition from peripheral [c] axes in regime 1 to a central [c] maximum in regime 3 is observed. Separate pole figures are calculated for different grain sizes, aspect ratios and long-axis trends of grains, and high and low levels of intragranular deformation intensity as measured by the mean grain kernel average misorientation (gKAM). Misorientation relations are analyzed for grains of different texture components (named Y, B, R and σ grains, with reference to previously published prism, basal, rhomb and σ1 grains). Results show that regimes 1 and 3 correspond to clear end-member textures, with regime 2 being transitional. Texture strength and the development of a central [c]-axis maximum from a girdle distribution depend on deformation intensity at the grain scale and on the contribution of dislocation creep, which increases towards regime 3. Adding to this calculations of resolved shear stresses and misorientation analysis, it becomes clear that the peripheral [c]-axis maximum in regime 1 is not due to deformation by basal 〈a〉 slip. Instead, we interpret the texture transition as a result of different texture forming processes, one being more efficient at high stresses (nucleation or growth of grains with peripheral [c] axes), the other depending on strain (dislocation glide involving prism and rhomb 〈a〉 slip systems), and not as a result of temperature-dependent activity of different slip systems.

Free energy of dislocations in a multi-slip geometry

The collective dynamics of dislocations is the underlying mechanism of plastic deformation in metallic crystals. Dislocation motion in metals generally occurs on multiple slip systems. The simultaneous activation of different slip systems plays a crucial role in crystal plasticity models. In this contribution, we study the energetic interactions between dislocations on different slip systems by deriving the free energy in a multi-slip geometry. In this, we restrict ourselves to straight and parallel edge dislocations. The obtained free energy has a long-range mean-field contribution, a statistical contribution and a many-body contribution. The many-body contribution is a local function of the total dislocation density on each slip system, and can therefore not be written in terms of the net dislocation density only. Moreover, this function is a strongly non-linear and non-convex function of the density on different slip systems, and hence the coupling between slip systems is of great importance.

Explore the anisotropic indentation pile-up patterns of single-crystal coppers by crystal plasticity finite element modelling

We report a new in-depth explanation of the anisotropic pile-up phenomenon based on the plastic slip theory. A crystal plasticity finite element method (CPFEM) model which considers plastic slips and lattice rotations as the only deformation mechanism has been developed to investigate the anisotropic pile-up behaviour of (001), (011) and (111) initially orientated single-crystal copper (Cu) undergoing nanoindentation. It is concluded that the activation of different slip systems contributes to the anisotropy of pile-up patterns.