Effect Of Grain Orientation Research Articles

Microscopic fatigue crack propagation model for polycrystalline alloys

In the present work, using the crystal plasticity finite element method in combination with the extended finite element method, a microscopic polycrystalline fatigue crack propagation (MPFCP) model based on the total cumulative shear strain was developed. MPFCP processes were reproduced well by the MPFCP model. The MPFCP behaviors of micro-single edge notched tensile (M−SENT) and micro-central cracked tension (M-CCT) model specimens under different constraint conditions were analyzed using the new model. Furthermore, the effects of grain orientation on the MPFCP rate and path were discussed. It was found that with the increase of constraints, the number of cycles required for the same MPFCP length increased for both M−SENT and M-CCT model specimens. A crack length of a = 100 μm was the transition length from the microstructurally small crack stage to the physically small crack stage. The diversity of grain orientation distribution had a significant influence on the MPFCP path and rate within each grain.

Grain engineering of high energy density BaTiO3 thick films integrated on Si

Ferroelectric (FE) ceramics with a large relative dielectric permittivity and a high dielectric strength have the potential to store or supply electricity of very high energy and power densities, which is desirable in many modern electronic and electrical systems. For a given FE material, such as the commonly-used BaTiO3, a close interplay between defect chemistry, misfit strain, and grain characteristics must be carefully manipulated for engineering its film capacitors. In this work, the effects of grain orientation and morphology on the energy storage properties of BaTiO3 thick films were systematically investigated. These films were all deposited on Si at 500 °C in an oxygen-rich atmosphere, and their thicknesses varied between ~500 nm and ~2.6 μm. While a columnar nanograined BaTiO3 film with a (001) texture showed a higher recyclable energy density Wrec (81.0 J/cm3vs. 57.1 J/cm3 @3.2 MV/cm, ~40% increase) than that of a randomly-oriented BaTiO3 film of about the same thickness (~500 nm), the latter showed an improved energy density at a reduced electric field with an increasing film thickness. Specifically, for the 1.3 μm and 2.6 μm thick polycrystalline films, their energy storage densities Wrec reached 46.6 J/cm3 and 48.8 J/cm3 at an applied electric field of 2.31 MV/cm (300 V on 1.3 μm film) and 1.77 MV/cm (460 V on 2.6 μm film), respectively. This ramp-up in energy density can be attributed to increased polarizability with a growing grain size in thicker polycrystalline films and is desirable in high pulse power applications.

Deformation mechanism in the mechanical response of nano polycrystalline HCP Zr and Zr-2.5 Nb: An atomistic study

Deformation-induced dislocations in polycrystalline hexagonal close-packed (HCP) metals have a great influence on the mechanical properties of materials. We use atomistic simulations to study the deformation behavior of Zr and Zr-2.5 Nb. We investigate the effects of grain orientation and loading directions on the nucleation and interactions of dislocations. We find that different deformation modes are activated under different loading directions, which may explain experimentally-observed superior mechanical strength under transverse loading than under radial loading. In addition, our simulations show that alloying leads to a more deformation-resistant material, due to the segregation of solute atoms to grain boundaries (GBs) as well as dislocation pinning, which makes emission from GBs more difficult. This study lays the foundation for investigating deformation through atomistic structural analysis.

An experimental study of anisotropic fatigue behavior of rolled ZK60 magnesium alloy

The strong anisotropy of wrought magnesium alloy significantly affects its application in structural components bearing fatigue loads. This study aims to explore the effects of grain orientations (RN-N versus RN-R) and sampling surfaces (RT-R versus RN-R) on the fatigue behavior of the ZK60 Mg alloy. Stress-controlled fatigue tests and quasi-in-situ EBSD tests were carried out on three different specimens. The sampling surface and grain orientation both have significant effects on the fatigue life of samples, especially at low-stress amplitude. Although the sampling methods are different, the three samples show similar cyclic evolution patterns. The consumption of available twins dominates the cyclic hardening behavior in the fatigue early stage. When loaded along ND, abundant intersecting twins induced by various variants can produce large plastic deformation, which is detrimental to the fatigue resistance of RN-N samples. When loaded along RD, the activation of specific twin variants leads to the reduction of the twinning areas, thus decreasing the plastic deformation of RN-R and RT-R samples. In addition, the constraint force along the width direction and sandwich-like metallographic structure of RN-R samples will hinder the activation and growth of twins, which results in smaller twinning areas and higher fatigue life than RT-R samples.

Anisotropic response in mechanical behavior of additively manufactured Al–Mn-Sc alloys by in-situ EBSD tensile tests

The anisotropic of microstructure for additively manufactured Al alloys is attributed to sharp temperature gradient during laser melting, resulting in anisotropy of mechanical properties. The correlation of grain orientation, size and aspect ratio on mechanical properties were investigated using in-situ EBSD tensile method on selective laser melting Al–Mn-Sc alloys in longitudinal section and cross section. The lattice rotation behavior and the effects of grain orientation, grain size and aspect ratio on mechanical anisotropy were explored. The predominant <001> orientation of the columnar crystals in the longitudinal section and the <102 > and <101> orientation that dominates the equiaxed crystals in the cross-section had a certain influence on the anisotropy of mechanical properties. The grains with different shapes and sizes exhibited different rotation behavior, and lattice rotation of equiaxed crystals with smaller grain sizes was more complex. By introducing anisotropy coefficients (Ka), the anisotropy sensitivity to grain orientations was revealed. Based on the anisotropy coefficient, grain size and aspect ratio, the mechanical anisotropy in both directions was accurately predicted.

Strengthening in tension and weakening in torsion in drawn nickel microwires

This study deals with the microstructure and texture effects on strength in tension and torsion testing of nickel microwires. Wire drawing was used to produce four different batches of microwires with a diameter of 100 μm with different mechanical treatments. Tension tests showed strain hardening with increasing yield strength upon an increase in drawing strain. However, the torsion tests showed an opposite trend, with a decrease in strength upon increasing wire drawing strain. This unexpected behavior in strengthening during torsion is attributed to the microtextures of drawn wires. Electron backscattered diffraction (EBSD) scans on the cross-sections of microwires revealed a core region texture with strong <111> fiber and a significantly different texture in the peripheral shell region. The fraction of <111> fiber increased with increasing drawing strain. A comparative analysis of Taylor factor M for uniaxial and shear loading of different texture fibers components showed that the effect of grain orientation on the mechanical strength is much higher in shear loading than the uniaxial loading. Crystal plasticity theory has been used to understand the impact of the loading conditions and rigid body rotations on the influence of deformation in grains with different orientations. The rate of hardening during torsion loading was more for microwires with increasing drawing strain, and this is attributed to the generation of more geometrically necessary dislocations in finer grained materials.

Microstructure evolution and mechanical behavior of copper through‑silicon via structure under thermal cyclic loading

The through‑silicon via (TSV) technique is widely applied in the latest highly integrated circuits packaging. However, one of the prevalent failure modes is caused by thermal cyclic loading from power fluctuations of the chip. Different thermal expansion coefficients of Cu and Si could cause a mismatch of thermal stresses under temperature cycling, which will lead to thermal fatigue failure of structure. In the current study, thermal cycling experiments are performed on Cu-TSV samples to investigate the effect of temperature cycling on microstructure evolution and mechanical behavior. The electron backscatter diffraction analysis is conducted to investigate the grain size, local texture and microstructure evolution of Cu. Based on the crystal plasticity theory, a constitutive model considering temperature and grain size effect is developed, and the parameters are calibrated. Combining crystal plasticity theory and finite element analysis, the effects of grain orientation and different grain sizes on the stress distribution and plastic work evolution of TSV structure under thermal cyclic loading are investigated.

Effects of grains‘ morphology on strengthening mechanisms in ODM401 14Cr ODS steel at high temperatures

The effect of grain orientation on the mechanical behavior of the 14Cr ODS steel (ODM401) at temperatures 400–800 °C is analyzed. The tensile and stress relaxation tests are performed on tensile specimens with grain orientation parallel and perpendicular to the extrusion direction. The strengthening mechanisms are analyzed in terms of the internal and thermal stress component, dislocation glide and climb and grain boundary creep. Models of strengthening mechanisms are used for evaluation of their intensity for a given temperature, grain orientation and macroscopic plastic strain level (0.001, 0.01, 0.025). Both grain orientations provide similar strengthening up to 600 °C. The grain orientation parallel to the extrusion direction provides higher strength at temperatures 700–800 °C due to the reduced grain boundary creep and dislocations annihilation at grain boundaries.

Life prediction and damage analysis of creep-fatigue combined with high-low cycle loading by using a crystal plasticity-based approach

Many high-temperature rotating components are always subjected to complex loading waveforms, arising the concerns for multi-damage driving crack initiation. In this paper, a series of strain-controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests as well as the novel creep-fatigue combined with high-low cycle (CF-HL) tests were performed in a nickel-based superalloy at 650 ℃. Then, post-test microstructure observations were carried out to reveal the damage mechanisms under the multi-damaged CF-HL loading based on the EBSD-TEM combinative characterizations. In this aspect, the single-slip-dominated deformation mechanism under CFI loadings transformed to double-slip-dominated one under CF-HL loading was revealed. Computationally, a numerical procedure with a combination of crystal plasticity theory and finite element implementation was constructed for predicting the CF-HL crack initiation life and quantifying the crack initiation mechanisms. With the help of the developed fatigue and creep indicator parameters represented by accumulated energy dissipation, good agreements between experimental data and simulated results were achieved within a scatter band of ± 2 on life prediction. In addition, the simulation results indicate that the combined effects of grain orientation and multiple slip system activation showed great influence on the CF-HL crack initiation.

Regionalization of microstructure characteristics and mechanisms of slip transmission in oriented grains deposited by wire arc additive manufacturing

Regionalization of microstructure regulation and mechanical property adjustment during the thermal cycle of the deposition process plays a vital role in the grain morphology and orientation of aluminum alloy components manufactured using wire arc additive manufacturing (WAAM) technology. However, the microscopic mechanism of the mechanical property difference caused by uneven microstructure in different regions remains unclear for the WAAM 2319 alloy. The geometric properties of grains are described quantitatively in different regions for the WAAM 2319 alloy through EBSD data processing and analysis. The effect of grain orientation on grain boundary, including subgrain boundaries and the boundary of coincidence site lattice (CSL boundary), are explored with EBSD data. The grain boundary and dislocations are characterized by transmission electron microscopy (TEM). The distribution of geometrically necessary dislocation (GND) in the WAAM block at different regions is studied through EBSD analysis. The high Schmidt factor or Taylor factor (M) percentage was quantitatively calculated in different regions. Then the relationship between grain morphology and plastic deformation ability is established through these factors. The results indicate that the average grain size is small and located in the top and middle of the WAAM sample with a low critical Taylor factor (Mc). The Taylor factor in most grains easily exceeds Mc (Mc < M), which causes most dislocations to pass through grain boundaries quickly, and plastic deformation easily occurs in these regions. There are various CSL boundaries except Σ3 boundaries existing in the middle of the sample, which can maintain the high mobility of the grain boundaries. Therefore, more slip transmission in the middle of the WAAM sample can provide the driving force for grain boundary migration. Most grains with a high subgrain boundary density (above 2.5) and the geometrically necessary dislocation (GND) density (5 × 1014 m−2) can hinder the movement of dislocations and improve the strength of materials at the sidewall of the sample. The Schmidt factor of columnar crystals is generally low (below 0.25), and the sliding system does not start rapidly in columnar crystals, especially at the bottom of the WAAM sample.

Understanding the Plastic Deformation of Gradient Interstitial Free (IF) Steel under Uniaxial Loading Using a Dislocation-Based Multiscale Approach

Gradient interstitial free (IF) steels have been shown to exhibit a superior combination of strength and ductility due to their multiscale microstructures. The novelty of the work resides in the implementation of a modified slip transmission and a back-stress quantity induced by a long-range dislocation interaction in the dislocation-based multiscale model. This is an improvement over the model we previously proposed. Simulations are performed on IF specimens with gradient structures and with homogeneous structures. The macroscopic behavior of the samples under tension and compression is studied. The evolution of the microstructure such as dislocations, geometrically necessary dislocations (GNDs), and the effects of grain orientation is analyzed. Results show that with our enhanced model, the simulations can successfully reproduce the stress-strain curves obtained experimentally on gradient nano IF steel specimens under tension. The simulations also capture the tension-compression asymmetry (TCA) in specimens with homogeneous and gradient microstructures. The initial texture is found to have a significant effect on the TCA of specimens with gradient microstructures.

A Geometry Optimization of Spiral Grain Selector During Directional Solidification of Nickel‐Based Superalloy

A spiral grain selector with excellent geometric parameters can ensure qualified single-crystal (SX) is selected while decreasing lesser thermal gradient (G) during casting of SX nickel-based superalloy . In this paper, three configurations of spiral grain selectors with different height of starter block (H = 18, 25, 35 mm) and same spiral passage are adopted. Based on the quantitative analysis of orientation distribution of grains in starter block, it is found that the deviation of <001> oriented grains in the projection zone of spiral passage inlet (circle with a diameter of 4 mm) are smaller than grains of overall cross-section (circle with a diameter of 10 mm), which verify that starter block with smaller diameter have better optimization effect of grain orientation. Moreover, the average deviation of <001> oriented grains decreases to a range of 6.6–10.8° when the height of starter block is 18–27 mm, and SX selection is completed on the position of less than half turn in spiral passage regardless of the number of grains in the inlet position. Finally, a modified spiral grain selector is designed from the perspective of practical production, of which total height is reduced by at least 15 mm, and can decrease lesser G at some extent during casting .

Effect of Grain Orientation on Hydrogen Embrittlement Behavior of Interstitial-Free Steel

In interstitial-free (IF) steel with a certain microtexture, the micro-orientation of grains is essential to understand the occurrence of hydrogen-induced cracking in body-centered cubic (BCC) structural steels. In this study, the hydrogen embrittlement (HE) susceptibility of IF steels was determined by slow strain rate tensile (SSRT) tests and hydrogen microprinting (HMT) experiments from the perspective of crystal orientation. The strength of the specimen with hydrogen was slightly higher than that without hydrogen, while the ductility and toughness were drastically reduced by hydrogen charging during the SSRT test. The HE susceptibility was characterized by the loss of elongation (Iδ) and toughness (Iψ), with losses of 46.3% and 70%, respectively. The microstructural observations indicate that cracks initiated along grains oriented in the {100} || normal direction (ND), and grain boundaries (GBs) around {100}||ND were prone to be enriched in hydrogen atoms; that is, {100} || ND showed poor resistance to intergranular cracking and susceptible to hydrogen segregation. HMT was used to confirm the above viewpoints. Meanwhile, the statistical results showed those high-angle misorientations of 50–60° deviation are the locations most vulnerable to fracture.

Orientation behavior in TRC-ZA21 magnesium alloy with fine grain size during nano-indentation process

The deformation behavior in magnesium alloy was greatly affected by grain orientation. It is crucial to analyze the relationship between deformation mechanism and grain orientation. In this study, the deformation behaviors in grains possessing different orientations for TRC-ZA21 alloy with fine grain size were investigated using the nano-indentation deformation coupling EBSD method. The effects of grain orientation and grain boundary on deformation behavior and propagation of deformation mechanism were discussed. The results illustrated that the irregular performance of the nano-mechanical properties could be attributed the inconsistency of grain orientation as well as the grain boundary misorientation angle. Grain orientation, followed by the criterion of Schmid factor, regulated the deformation mechanism of grains that were in direct contact with the nano-indenter. This signified the orientation dependence in plastic deformation. The deformation behavior in grains, induced by plastic deformation and indirectly in contact with the nano-indenter, was found to be influenced by the grain boundary. The orientation difference in adjacent grains determines the influence of grain boundary in plastic deformation, revealing the competitive and coordinative behavior associated with these deformation mechanisms. The c-axes angle between adjacent grains was the key factor to determine the influence of grain boundary on deformation propagation.

Deformation mechanism of ferrite in a low carbon Al-killed steel: Slip behavior, grain boundary evolution and GND development

The forming quality and performance of double walled brazed tube formed by steel sheet are seriously affected by the deformation behavior of the initial sheet. In this work, the deformation mechanism of ferrite in a low carbon Al-killed steel sheet was investigated by in situ tensile and electron backscatter diffraction (EBSD) tests. It is found that ferrite presents single slip, double slip and cross slip as well as slip transfer behavior in the deformation process. The activation of the {110}<111> slip system is the main deformation mode, the less activation number of {112}<111> and {123}<111> is due to the orientation dependence and high critical resolved shear stresses (CRSS), respectively. A high Schmid factor (SF) or geometric compatibility factor m' will contribute to slip transfer. Meanwhile, the evolution of low angle grain boundaries (LAGBs) is the main deformation feature for ferrite polycrystals, and the fraction of 2–5° LAGBs in the whole LAGBs shows a strong linear relationship with strain. The subdivision of grains and rotation of different parts lead to the gradual evolution of LAGBs into high angle grain boundaries (HAGBs). Furthermore, small grains are more likely to accumulate the geometrically necessary dislocation (GND) because the microstructural unit size restricts the movement of dislocation, while the less effect of grain orientation is related to the high SF for all grains.

Deformation mechanisms of Al thin films: In-situ TEM and molecular dynamics study

Molecular dynamics (MD) is a simulation method regularly used for examining the mechanical properties of materials on an atomic level. Despite many reasonable results obtained by this method, it remains unclear how well an MD simulation can reproduce the results of a specific experiment. Thin aluminum-based films were deformed in-situ in a transmission electron microscope (TEM). Grain boundary processes were identified as the primary deformation mechanism, and grain rotations during deformation were confirmed by automatic orientation maps. Tensile deformation of Al-based thin films with columnar grains corresponding to the material structure observed in the experiment was then simulated using MD. Several main attributes of the simulation were found to match the experimental results. The effect of grain orientation on intragranular dislocation activity was observed by TEM and confirmed by MD simulations.

A comparative study of microstructures and nanomechanical properties of additively manufactured and commercial metallic stents

Additive manufacturing emerges as an innovative technology to fabricate medical stents used to treat blocked arteries. However, there is a lack of direct comparison of underlying microstructure and mechanical properties of additively manufactured and commercial stents. In this study, additively manufactured and commercial 316 L stainless steel stents were investigated comparatively, with electrochemical polishing being used to improve the surface finish of the former stent. Microstructural characterisation of both stents was carried out through optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Their hardness and elastic modulus were studied using Berkovich nanoindentation, with an emphasis on the effect of grain orientation. In addition, spherical nanoindentation was used to generate indentation stress-strain curves based on load-displacement responses. The obtained results showed that electrochemical polishing was effective in diminishing the average surface roughness, with a reduction of Ra value from 8.45 µm to 5.96 µm. The additively manufactured stent demonstrated the hierarchical grain microstructure with columnar grains and cellular sub-grains, as opposed to equiaxed fine grains and twins in the commercial stent. The hardness and modulus of additively manufactured stents were higher than those of the commercial ones. The grains close to the (111) orientation exhibited the highest hardness and elastic modulus followed by (101) and (001) orientations. The indentation stress-strain curves, yield strength, and hardening behaviour were similar for the additively manufactured and commercial stents. This work provides a fundamental understanding of the microstructure and properties of the additively manufactured stent and represents an important step towards innovative manufacturing of stents.

Short communication: Experimental factors affecting fission-track counts in apatite

Abstract. The tools for interpreting fission-track data are evolving apace, but, even so, the outcomes cannot be better than the data. Recent studies showed that track etching and observation affect confined-track length measurements. We investigated the effects of grain orientation, polishing, etching and observation on fission-track counts in apatite. Our findings throw light on the phenomena that affect the track counts and hence the sample ages, whilst raising the question: what counts as an etched surface track? This is pertinent to manual and automatic track counts and to designing training strategies for neural networks. Counting prism faces and using the ζ calibration for age calculation are assumed to deal with most etching- and counting-related factors. However, prism faces are not unproblematic for counting, and other surface orientations are not unusable. Our results suggest that a reinvestigation of the etching properties of different apatite faces could increase the range useful for dating and lift a significant restriction for provenance studies.

Crystal Plasticity Simulation of Yield Loci Evolution of SUS304 Foil.

The deformation process of metal foils is usually under a complex stress status, and the size effect has an obvious influence on the microforming process. To study the effect of grain orientation and grain size distribution on the yield loci evolution of SUS304 stainless steel foils, three representative volume element (RVE) models were built based on the open source tools NEPER and MTEX. In addition, the yield loci with different grain sizes are obtained by simulation with Duisseldorf Advanced Material Simulation Kit (DAMASK) under different proportional loading conditions. The initial yield loci show a remarkable difference in shape and size, mainly caused by the distinct texture characteristics. By comparing the crystal plasticity simulation with the experimental results, the model with normal grain size distribution and initial texture based on Electron Back-scattered Diffraction (EBSD) data can more accurately describe the influence of the size effect on the shape and size of yield loci, which is the result of the interaction of grain size distribution and texture. However, the enhancement of grain deformation coordination will weaken the impact of the size effect on yield loci shape if the grain size distribution is more uniform.

Effect of Grain Orientation on the Microscopic Corrosion Behavior of Pure Zinc

Effect of Grain Orientation on the Microscopic Corrosion Behavior of Pure Zinc