Grain Boundary Misorientation Angle Research Articles

Characterizing the role of adjoining twins at grain boundaries in hexagonal close packed materials

Hexagonal close packed (HCP) Mg and Zr are being used in transportation and nuclear industries, respectively. The ductility and formability of these materials is significantly limited by the activation of prevalent deformation twinning. Twins in HCP polycrystals usually nucleate at grain boundaries (GBs), propagate into the grain, and they either terminate at opposing GBs (isolated-twins) or transmit into a neighboring grain (adjoining-twin-pairs: ATPs). Because twin interfaces provide a path for crack propagation, twin transmission is relevant to material ductility. This study combines electron backscatter diffraction (EBSD) based statistical analysis of twinning microstructures and crystal plasticity modeling, to characterize twin thickening processes away from and near GBs. Analysis of deformed Mg and Zr microstructures reveals that local twin thicknesses at GBs are statistically larger for ATPs compared to isolated-twins. Further, thicknesses are found to decrease with increasing GB misorientation angle. Full-field Fast-Fourier-Transform micromechanics modeling shows that shear-transformation induced backstress are locally relaxed at GBs for ATPs, but not for isolated-twins. As a consequence, ATPs can thicken locally at GBs and the preferential site for twin thickening shifts from the middle of the twin to common GB.

Characterization of Kapitza resistances of natural grain boundaries in cerium oxide

In this study, the Kapitza resistances of natural grain boundaries of Cerium Oxide (CeO2) at room temperature was experimentally determined and correlated with the grain misorientation. A spatial-domain thermoreflectance technique (SDTR) was used as the characterization tool and the Kapitza resistances of the target grain boundaries were obtained from solving the inverse heat conduction problem through a multi-parameter fitting process. The measurements were performed at ∼70 different grain boundaries with the size of adjacent grains larger than approximately 100 µm. From more than 50 sets of effective data, the average interfacial thermal resistance is measured as (8.95 ± 0.68) × 10−9 m2K/W, which is consistent with results from other studies. The grain orientations from five selected locations with good data quality were characterized by electron backscatter diffraction (EBSD). A direct correlation between Kapitza resistances and misorientation angles of high-angle grain boundaries was found.

Thermal conductivity of graphene grain boundaries along arbitrary in-plane directions: A comprehensive molecular dynamics study

The thermal conductivity of polycrystalline graphene is expected to be lower than that of pristine graphene, due to the existence of defects, such as grain boundaries (GBs). To study the thermal transport behavior in polycrystalline graphene, it is crucial to understand the thermal conductivity of graphene GBs as a function of the tilt GB misorientation angle and in-plane thermal loading angle. However, existing studies of thermal conductivity of graphene GBs only consider the case where the thermal flux is perpendicular or parallel to the graphene GB. To address this issue, here we perform systematic non-equilibrium molecular dynamics simulations and investigate the thermal conductivity of graphene GBs for all possible tilt GB misorientation angles (23 cases) under arbitrary in-plane thermal loading directions. The findings from the present study can offer quantitative guidance for using polycrystalline graphene in thermal devices and flexible electronics applications.

Enhancement of Hot Corrosion Resistance of Modified 9Cr-1Mo Steel Through Surface Nanostructuring and Pre-oxidation

Nanosize grains of ~ 65 nm were developed with large misorientation angles of grain boundaries in surface region of normalized and tempered modified 9Cr-1Mo steel by ultrasonic shot peening (USSP) with hard steel balls of 3 mm diameter. The surface roughness and the depth of nanostructured surface region were found to increase with the duration of USSP from 0.5 to 5 min. Hot corrosion tests were performed for the Un-USSP and the samples USSPed for the durations of 0.25 and 1.5 min and also for the samples subjected to USSP and subsequently pre-oxidation at 600 °C for 4 h. The hot corrosion resistance at 600 °C under 100% NaCl coating was significantly improved by USSP for 1.5 min and subsequent pre-oxidation at 600 °C for 4 h. The results are discussed in terms of the formation of more uniform and effective protective iron–chromium oxide layer on the USSPed surface from the subsequent pre-oxidation treatment, prior to hot corrosion of the specimens under 100% NaCl coating at 600 °C.

Combined effects of cooperative grain boundary sliding and migration and reinforced particles on crack growth in fine-grained Mg alloys

A theoretical model is developed to describe the combined influences of cooperative grain boundary (GB) sliding and migration and reinforced particles on crack propagation in fine-grained Mg alloys. The numerical solutions of singular integral equations are derived on the basis of complex variable method of Muskhelishvili, the superposition principle of elasticity and distributed dislocation technique. The expressions of stress intensity factors (SIFs) near the right tip of basal crack are obtained and the energy release rate (ERR) characterizing the condition for crack growth is calculated. The influences of important parameters such as the location of cooperative GB sliding and migration, the size of reinforced particle and the misorientation angle of higher angle grain boundaries on the ERR are discussed in detail. The results show that the fracture toughness of fine-grained Mg alloys can be improved by cooperative GB sliding and migration and particle hardening and refining. There exists an optimum particle size that makes the fracture toughness of fine-grained Mg alloys best. Besides, the GB migration remarkably contributes to the fracture toughness of fine-grained Mg alloys and there is an optimum migration distance making the fracture toughness of fine-grained Mg alloys best.

Kapitza conductance of symmetric tilt grain boundaries of monolayer boron nitride

We use reverse nonequilibrium molecular dynamics simulations to study thermal conductivity of two–dimensional hexagonal boron nitride (h–BN) nanoribbons containing symmetric tilt grain boundaries. The simulations are conducted on periodic h–BN nanoribbons with zigzag and armchair chirality. The effective thermal conductivity of ribbons and Kapitza conductance of grain boundaries are calculated by inducing a constant heat flux along the longitudinal direction of ribbons. The steady state temperature profiles of nanoribbons display jumps at the location of grain boundaries. The temperature jumps monolithically increases with the misorientation angle of grain boundaries indicating that grain boundaries with higher misorientation angle have lower Kapitza conductance. The lower Kapitza conductance is due to higher phonon scattering at grain boundaries which is a result of a higher mismatch between the phonon spectra of grain boundary and grain atoms. Our modeling results also predict that by increasing the length, both Kapitza conductance of grain boundaries and effective thermal conductivity of ribbons increases. Although temperature does not have a significant impact on Kapitza conductance, but by increasing temperature effective thermal conductivity of ribbons decreases.

Tungsten content and grain boundary misorientation angle effect on crack blunting in nanocrystalline Ni-W alloy

The effect of tungsten (W) content and grain boundary misorientation angle (GBMOA) on crack blunting of nanocrystalline Ni-W alloy (20–100 nm) is researched theoretically, considering the coupled effects of dislocations and grain boundaries (GBs). In our proposed model, W atoms are clustered in the dislocation free region (DFZ), impeding dislocation slip, and W additions lead to GB segregation so that the boundary energy is reduced. The dislocations emitted from the crack tip are stopped at or/and penetrated through GBs, which depends on the total force acting on the dislocations as well as the critical penetration stress. The critical penetration stress is bound up with GB energy and residual Burgers vector. The number of dislocations emitted from the crack tip and penetrated through GB is calculated by using W content and GBMOA. The results show that an increase in W content decreases the critical penetration stress and increases the number of dislocations emitted from the crack tip. The critical stress intensity factors by considering the interactions between dislocations and GBs are larger than those of dislocations stayed at GBs. It is demonstrated that crack blunting depends significantly on both W content and GBMOA.

Phase-field-crystal study on the evolution behavior of microcracks initiated on grain boundaries under constant strain

The initiation and propagation behavior of microcracks is closely associated with the cleavage of crystalline materials. We use phase-field-crystal method to explore the evolution process and mechanism of microcracks initiated on grain boundaries (GBs). Constant biaxial strain is applied to the (0001) crystal plane of hexagonal close-packed bicrystal. Under applied strain, cracks are initiated at the end of semi-boundaries between grains. Following this crack initiation (CIN) mechanism, grain boundary misorientation angle (GBMA) can greatly affect the process of crack initiation and propagation (CINPR) in normal GB system. Along with the increase in GBMA, CIN is promoted and the type of subsequent crack propagation changes from trans-granular propagation into inter-granular propagation. System temperature and applied strain also have influence on CINPR. Associated with fracture mechanics theory, the effects of GBMA, temperature and strain on the behavior of CINPR are investigated. Additionally, we give curves of change in free energy to illustrate these effects from energy perspective. Crack arrestment mechanism, especially the plastic relaxation mechanism, is also discussed. The simulation results acquired in this work are in good agreement with theoretical analyses and experimental results.

Effect of microcrystallites formed by deformation on the growth and orientation of grains during recrystallization of iron

The changes of ultradispersed structure in deformed iron after annealing has been investigated. An ultradispersed structure of two different types—cellular and submicrocrystalline (SMC)—has been formed in iron by high pressure torsion deformation. The effect of the deformed-structure type on the temperature of recrystallization onset, the size of recrystallized grains, and the recrystallization texture has been understood. The comparison of recrystallization of the initial cellular and SMC structures should be made to determine the role of microcrystallites. The recrystallization temperature of iron with an SMC structure is 200–250°С lower than that with a cellular structure, because of the presence of microcrystallites, ready recrystallization nuclei. The recrystallization (annealing at 750°C, 1h) of the cellular structure results in the formation of a coarse-grained structure with an average recrystallized grain size that is by an order of magnitude coarser than that after the same annealing of the SMC structure (5 and 180 μm, respectively). The significant distinct feature of the SMC structure in contrast to the cellular one is the annealing-assisted formation of a <110> recrystallization texture in it, whereas the annealing of iron with the cellular structure does not cause the formation of a recrystallization macrotexture. An increase in the sharpness of the recrystallization texture correlates with a decrease in the average grain-boundary misorientation angle.

Incorporating the grain boundary misorientation effects on slip activity into crystal plasticity

ABSTRACTThe role of grain boundary misorientation angle (GBMA) distribution on slip activity in a high-manganese austenitic steel was investigated through experiments and simulations. Crystal plasticity simulations incorporating the GBMA distribution and the corresponding dislocation–grain boundary interactions were conducted. The computational analysis revealed that the number of active slip systems decreased when GBMA distribution was taken into account owing to the larger volume of grain boundary–dislocation interactions. The current results demonstrate that the dislocation–grain boundary interactions significantly contribute to the overall hardening, and the GBMA distribution constitutes a key parameter dictating the slip activity.

The Effects of Grain Boundaries on the Current Transport Properties in YBCO-Coated Conductors.

We report a detailed study of the grain orientations and grain boundary (GB) networks in Y2O3 films grown on Ni-5 at.%W substrates. Electron back scatter diffraction (EBSD) exhibited different GB misorientation angle distributions, strongly decided by Y2O3 films with different textures. The subsequent yttria-stabilized zirconia (YSZ) barrier and CeO2 cap layer were deposited on Y2O3 layers by radio frequency sputtering, and YBa2Cu3O7-δ (YBCO) films were deposited by pulsed laser deposition. For explicating the effects of the grain boundaries on the current carry capacity of YBCO films, a percolation model was proposed to calculate the critical current density (Jc) which depended on different GB misorientation angle distributions. The significantly higher Jc for the sample with sharper texture is believed to be attributed to improved GB misorientation angle distributions.

Energetic and thermal properties of tilt grain boundaries in graphene/hexagonal boron nitride heterostructures

Graphene/hexagonal boron nitride (G/h-BN) heterostructure has attracted tremendous research efforts owing to its great potential for applications in nanoscale electronic devices. In such hybrid materials, tilt grain boundaries (GBs) between graphene and h-BN grains may have unique physical properties, which have not been well understood. Here we have conducted non-equilibrium molecular dynamics simulations to study the energetic and thermal properties of tilt GBs in G/h-BN heterostructures. The effect of misorientation angles of tilt GBs on both GB energy and interfacial thermal conductance are investigated.

The favourable large misorientation angle grain boundaries in graphene.

A grain boundary (GB) in graphene is a linear defect between two specifically oriented graphene edges, whose title angles are denoted as θ1 and θ2, respectively. Here we present a systematic theoretical study on the structure and stability of GBs in graphene as a function of the misorientation angle, Φ = (θ1-θ2) and the GB orientation in multi-crystalline graphene, which is denoted by Θ = (θ1 + θ2). It is surprising that although the number of disorders of the GB, i.e., the pentagon-heptagon pairs (5|7s), reaches the maximum at Φ∼ 30°, the GB formation energy versus the Φ curve reaches a local minimum. The subsequent M-shape of the Efvs. the Φ curve is due to the strong cancellation of the local strains around 5|7 pairs by the "head-to-tail" formation. This study successfully explains many previously observed experimental puzzles, such as the multimodal distribution of GBs and the abundance of GB misorientation angles of ∼30°. Besides, this study also showed that the formation energy of GBs is less sensitive to Θ, although the twin boundaries are slightly more stable than others.

An ab-initio investigation of the effect of graphene on the strength-electron density correlation in SiC grain boundaries

Recent developments in SiC based ceramic materials have shown a possibility of graphene dispersion at grain boundaries (GBs) significantly modifying bulk thermomechanical properties. Graphene and SiC have been known to have significant electronic affinity for each other. This work presents an electronic density of states-mechanical strength correlation based understanding of the effect of graphene layer defects on the tensile strength of selected 3C–SiC GBs that incorporate graphene layers. The tensile deformation simulations are performed using Car–Parrinello molecular dynamics (CPMD) method. Three different SiC GBs are examined (unit GB, ∑3 tilt SiC GB, and ∑9 tilt SiC GB). For each examined GB type, graphene layers with four different defect types are examined. Analyses establish quantitative correlation between the tensile strength of the examined GBs and graphene defect type in GBs. Of the defects examined, double vacancy defect most significantly deteriorates GB strength. GB failure strain is mainly determined by graphene cleavage fracture strain. Graphene cleavage is accompanied by monoatomic carbon chain formation, pentagon ring formation, and heptagonal ring formation. The specific mechanism closely depends upon the graphene–SiC interaction strength defined based on total electron density of states. The interaction strength variation is found to be closely correlated to the tensile strength variation in GBs. Examination of electron density variation points to specific sites of graphene cleavage fracture that correlates to earlier failure mechanism observations. Observations are used to predict strength of SiC GBs as a function of GB misorientation angle. The developed relation predicts other reported values in literature quite closely.

Effects of mechanical force on grain structures of friction stir welded oxide dispersion strengthened ferritic steel

The weldability of oxide dispersion strengthened (ODS) ferritic steels is a critical obstructive in the development and use of these steels. Friction stir welding has been considered to be a promising way to solve this problem. The main purpose of this work was to reveal the effects of mechanical force on grain structures of friction stir welded ODS ferritic steel. The grain appearances and the misorientation angles of grain boundaries in different welded zones were investigated by the electron backscatter diffraction (EBSD). Results showed that the mechanical force imposed by the stir tool can activate and promote the recrystallization characterized by the transformation of boundaries from LABs to HABs, and contribute to the grain refinement. The type of recrystallization in the stir zone can be classified as the continuous dynamic recrystallization (CDRX).

In situ determination of misorientation angle of grain boundary by field ion microscopy analysis

We proposed an advanced analysis technique for characterizing a grain boundary using field ion microscopy (FIM) for atom probe analysis. The technique enables quick and precise estimation of the misorientation angle of the grain boundary by matching the calculated crystallographic pole positions with the actual FIM image including the grain boundary. We investigated the accuracy in estimation of the misorientation angle using target grain boundaries which had been analyzed by electron backscatter diffraction pattern (EBSD) analysis. From the comparison between EBSD and FIM analyses, we found that the technique enables the determination of the misorientation angle with a high accuracy of ± 0.4°, which is comparable with that achieved by EBSD.

Misorientation effect of grain boundary on the formation of discontinuous precipitation in second and third generation single crystal superalloys

[001] tilt artificial grain boundaries of Ni-based single crystal superalloys CMSX-4 and DD10 have been prepared by self-diffusion bonding. The microstructural stability of 0 ∼ 30∘ artificial grain boundaries have been investigated after heat treatment at 1100 ∘ C for 0 ∼ 300 h. TCP phases and cellular colony developed on boundaries are related to misorientation angle of the bonded boundaries of DD10 and DD10 alloys as well as the bonded boundaries of CMSX-4 and DD10 alloys. The heterogeneous nucleation of TCP phase, enveloped by γ′ film, occurred along 15∘ and 20∘ boundaries. Discontinuous Precipitation (DP) reaction occurred along high misorientation angle (20∘ ∼ 30∘ ) boundaries. However, no TCP phase formation existed along grain boundaries with different misorientation angles in CMSX-4/CMSX-4 bonded alloys as well as for a 0∘ boundary in DD10/DD10 and CMSX-4/DD10 bonded alloys. The current study clearly suggests that grain boundary precipitation and its morphology were influenced by the misorientation angle of grain boundary and the content of refractory elements in alloy.

Severe plastic deformation of commercial purity aluminum by rotary swaging: Microstructure evolution and mechanical properties

The microstructure evolution and change in mechanical properties of commercially pure aluminum (Al 1050) were investigated during severe plastic deformation by rotary swaging (RS) at ambient temperature. Optical microscopy (OM) and scanning electron microscopy (SEM) using electron back scatter diffraction (EBSD) were utilized to document the evolution of the microstructure. Hardness and tensile tests were conducted to characterize mechanical properties. Rotary swaging was found to lead to a marked decrease in grain size. The microstructure consisted of cell structure of low angle grain boundaries (LAGBs) within bigger grains. After heavy swaging to true deformation degree of φ=3, the microstructure was quite uniform normal to flow direction in terms of cell size, average misorientation angle and content of low angle grain boundaries. Extremely fine dynamically recrystallized grains, heterogeneously nucleated at existing grain boundaries were evident on the section parallel to the flow direction. As compared to the as-received condition, the yield stress and ultimate tensile strength of the material was strongly increased by a factor of 8 and 2.3, respectively. Furthermore, the elongation to fracture was drastically reduced as was the uniform strain indicating a marked reduction in work hardening capability.

Nanostructural analysis of ZnO:Al thin films for carrier-transport mechanisms

The carrier mobility of sputter-deposited Al-doped ZnO transparent-conducting (ZnO:Al) thin films was controlled between 22 and 48 cm2/Vs by varying the ZnO:Al seed layer. The statistical distribution of the [001] grain misorientation was characterized from the X-ray diffraction rocking curve in the range from 0.043 (2.5°) to 0.179 rad (10.2°). The grain-boundary energy barriers (Eb) from Seto's model [1] clearly exhibit linear dependence on the grain-boundary misorientation angle (ω) according to the equation Eb = 78 ± 4 + 173 ± 32 ω meV.

Influence of grain boundaries misorientation angle on intergranular corrosion in 2024-T3 aluminium

The special attention has been paid to the influence of misorientation angle of a random grain boundary (GB) on susceptibility to intergranular attack. The detailed observations of the microstructure of the intergranular corrosion (IGC) in 2024-T3 aluminium alloy (AA2024-T3) subjected to galvanic corrosion tests in two different solutions containing chloride ions (0.1 M and 0.5 M NaCl) were carried out using Scanning Electron Microscopy (SEM). The Electron Backscattered Diffraction (EBSD) technique was used to determine the grain boundary character distribution (GBCD) in the initial sample and a GBCD of corroded grain boundaries on a sample subjected to the corrosion test. The results are discussed in terms of the influence of the misorientation angle on the susceptibility of the grain boundaries to corrosion.