Grain Boundary Effects Research Articles

Effects of surface and grain boundary on temperature-pressure nano-phase diagrams of nanostructured carbon

Temperature-pressure phase diagrams can provide guidance for materials preparation and application, but nano-phase diagrams are scarce. Coordination environment of atoms located at surface and grain boundary differs to that of interior ones, indicating non-negligible surface and grain boundary effects on nano-phase transitions. The surface effect was universally considered in previous theoretical models, but its size-dependence was ignored. Moreover, the grain boundary effect was rarely explored. Here, the surface and grain boundary effects are modeled using a thermodynamic approach to construct the nano-phase diagrams of nanostructured carbon. As the size is reduced, additional pressures induced by these two effects rise, contributing to the transition from thermodynamically stable phase to metastable one, and the phase boundary shifts to low temperature and low pressure. Our prediction agrees well with available literature results.

Nanoscale friction of CVD single-layer MoS2 with controlled defect formation

Two-dimensional (2D) layered nanomaterials such as graphene, molybdenum disulfide (MoS2), or tungsten disulfide offer a promising solution in areas of solid-state lubrication, due to their excellent mechanical properties as well as low friction. However, defects can influence their friction and reduce their superior tribological properties. Thus, it is crucial to understand the effects of defects on sliding behavior in 2D nanomaterials, to foster a functional strategy for utilizing 2D nanomaterials as solid-state tribological films. In this study, frictional effects of defects, grain boundaries, and atomic-scale structural defects were explored on chemical vapor deposition (CVD) grown single layer MoS2. Selective patterning of defects into MoS2 was accomplished via controlled irradiation of helium ions with varying ion doses. The friction of MoS2 was characterized by friction force microscopy (FFM) and was found that friction depends on the defect formation controlled by helium ion irradiation. This approach offers a correlation between surface topography, defects and friction. Understanding the relative friction of MoS2 in the presence of different levels of defects is foundational to studying tribological properties of a single layer MoS2 at both nanoscales and macroscales.

Effect of grain boundaries on elastic shock wave in graphene

Effect of grain boundaries (GBs) on elastic shock wave in graphene is investigated by molecular dynamics simulations. Bicrystal graphenes with symmetrical GB are shocked along directions perpendicular and parallel to GB. For perpendicular shock loadings, double elastic shock waves emerge in form of quasilongitudinal (QL) and quasitransverse (QT) waves, since the loading direction is neither zigzag nor armchair. GB attenuates the QL wave and gives rise to new QT waves propagating into grains. Transverse particle motion in the elastic shocks can induce small lattice rotations and different oriented regions, whose number increases upon the passage of waves through GB. Upon shock loadings along GB, transverse particle motions of opposite direction generate in the two grains, and change the pressure distribution right behind wavefront, and then result in deviation of shock wave from planar loading or “V” shaped wavefront turning at GB. The above phenomena are attributed to the turn of grain orientation at GB and transverse particle motions induced by lattice symmetry reduction upon shock compression.

Regulating the lithium metal growth by Li3BO3/Li2OHCl solid-state electrolyte for long-lasting lithium metal stripping-plating

Lithium-rich anti-perovskite materials, with their high theoretical Li + conductivity and relatively low energy barrier for Li + transport, are highly promising as an electrolyte contender in all-solid-state lithium-metal batteries. Their current performance is however compromised by the grain boundary to result in low Li + conductivity and high activation energy. Herein, a composite electrolyte is prepared by introducing the glassy Li 3 BO 3 into the Li 2 OHCl to serve as a bridge to connect the Li 2 OHCl grains together to lower the impact from the grain boundary. The Li + conductivity of Li 2 OHCl can be improved by the presence of 10 wt% Li 3 BO 3 , and its impact on the lithium metal growth behavior is also investigated. It is found that the lithium-metal battery with Li 3 BO 3 /Li 2 OHCl prefers the deposition of lithium metal particles with larger size than that in the battery with Li 2 OHCl. Consequently, the lithium-metal symmetric cell with 10 wt% Li 3 BO 3 /Li 2 OHCl is able to display excellent cycling for over 1800 h at 0.1 mA cm −2 . The batteries with 10 wt% Li 3 BO 3 /Li 2 OHCl are also able to improve the cycle stability and rate performance. The results of this study provide the direct experimental proof of the effect of grain boundary in Li 2 OHCl on the battery performance. • The grain boundary barrier of LiRAP Li 2 OHCl was reduced by glassy Li 3 BO 3 . • Lithium nucleation and growth behaviors in Li 2 OHCl-based battery were investigated. • The cell with Li 3 BO 3 /Li 2 OHCl showed excellent lithium stripping-plating cycling. • The effect of grain boundary in Li 2 OHCl on the battery performance was studied.

Growth behavior and kinetics of austenite grain in low-carbon high-strength steel with copper

A low-carbon high-strength steel with copper has better antibiological corrosion property, more widely used in large marine projects and ships. In this study, an austenite grain growth model of a low-carbon ship plate steel with 1.6Cu was established by using Sellars equation at 900 °C–1200 °C and different holding times (30–120 min) to reveal its kinetics. The pinning effect of grain boundary precipitates was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and a quantitative relationship between the solid solution and precipitation behavior of copper bearing precipitates in experimental steel and austenite grain growth was analyzed. The experimental results show that the austenite grains grow slowly, and the grains are fine grains when the heating temperature is below 1000 °C and the transition temperature of rapid grain coarsening is 1000 °C. The relative error of dynamic model can be controlled within 8.5%. During heat treatment, Cu atoms are segregated at the grain boundary to form a copper-rich region, providing a coating effect on the carbide and grain boundary and hindering the growth of grains. With the increase in temperature, the diffusion rate of copper atoms increases, and the precipitates containing copper are rapidly dissolved into austenite. Therefore, the pinning effect is weakened, and the austenite grains grow rapidly.

Study of Micro-Upsetting by Finite Element Simulation Based on Crystal Plasticity and Grain Boundary Strengthening Theories

The properties of individual grains affect the mechanical behaviors and response of materials in micro-scaled deformation, viz., microforming, and there are unknown phenomena and deformation behaviors existing and limiting the wide application of microforming due to size effect. In this paper, a composite model combining crystal plasticity and grain boundary strengthening theories was developed for numerical investigation into the effect of grain boundaries on the plastic deformation of copper micro-upsetting. By comparing the results with and without grain-boundary structure, it is revealed that grain boundaries, which act as the barriers of crystal slip, result in the enhanced flow stress and the discontinuous distribution of stress and strain. The grain size effect is also considered in this research, and the results show the coarse-grained material reduces the flow stress and enhances the inhomogeneous deformation.

Impedance and Electrical Evaluation of Rare Earth-Based Perovskite: BiYbO3

The rare earth element ytterbium based lead-free perovskite BiYbO3 was successfully synthesized by cost effective solid-state reaction technique. The analysis of the XRD reflection peaks revealed that BiYbO3 crystallizes with cubic [Formula: see text] single phase crystal system having cell parameter [Formula: see text][Formula: see text]Å. The decrease in the dielectric permittivity with frequency was found to follow the accepted Maxwell–Wagner model of interfacial polarization. The reported perovskite was found to be stable up to [Formula: see text]C as evident from the low [Formula: see text] values. The bulk capacitance of BiYbO3 decreases from 1.619[Formula: see text]nF/cm2 to 0.173[Formula: see text]nF/cm2 with the rise in temperature from [Formula: see text]C to [Formula: see text]C. The dielectric data shows that BiYbO3 perovskite follows a negative temperature coefficient of resistance (NTCR) trend. The information obtained from the Nyquist plot and the Cole–Cole electric modulus plot is complementary to each other. The effect of bulk and grain boundary is clearly visible in the Cole–Cole electric modulus plot, whereas a good fit of the equivalent circuit [Formula: see text] in the Nyquist plot gave important bulk and grain boundary (capacitance and resistance) parameters. The AC-conductive study for this rare earth perovskite is used to obtain the activation energies to understand the semiconducting behavior of BiYbO3.

Evaluation of local stress state due to grain-boundary sliding during creep within a crystal plasticity finite element multi-scale framework

Previous studies demonstrate that grain-boundary sliding could accelerate creep rate and give rise to large internal stresses that can lead to damage development, e.g. formation of wedge cracks. The present study provides more insight into the effects of grain-boundary sliding (GBS) on the deformation behaviour of realistic polycrystalline aggregates during creep, through the development of a computational framework which combines: i) the use of interface elements for sliding at grain boundaries, and ii) special triple point (in 2D) or triple line (in 3D) elements to prevent artificial dilation at these locations in the microstructure with iii) a physically-based crystal plasticity constitutive model for time-dependent inelastic deformation of the individual grains. Experimental data at various scales is used to calibrate the framework and compare with model predictions. We pay particular consideration to effects of grain boundary sliding during creep of Type 316 stainless steel, which is used extensively in structural components of the UK fleet of Advanced Gas Cooled Nuclear Reactors (AGRs). It is found that the anisotropic deformation of the grains and the mismatch in crystallographic orientation between neighbouring grains play a significant role in determining the extent of sliding on a given boundary. Their effect on the development of stress within the grains, particularly at triple grain junctions, and the increase in axial stress along transverse boundaries are quantified. The article demonstrates that the magnitude of the stress along the facets is highly-dependent on the crystallographic orientations of the neighbouring grains and the relative amount of sliding. Boundaries, transverse to the applied load tend to carry higher normal stresses of the order of 100-180 MPa, in cases where the neighbouring grains consist of plastically-harder crystallographic orientations. An approach to estimate the amount of sliding as a function of GB particle morphology and diffusive accommodation is developed and employed. The possible implications of these findings on the initiation of creep damage are commented on.

Investigation on the Effects of Grain Boundary on Deformation Behavior of Bicrystalline Pillar by Crystal Plasticity Finite Element Method

A dislocation density–grain boundary interaction scheme coupled with the dislocation density-based crystalline plasticity finite element method has been established and used to investigate the deformation behavior of bicrystalline pillars with the same grain boundary misorientation angle but different crystal orientations. It is found that the angle between the activated slip systems, which is determined by the crystal orientations, rather than the grain boundary misorientation angle, influences the interactions between the plastic slip and the grain boundary, which further influence the heterogeneous deformation of bicrystalline specimens.

The Effect of Grain Boundary on Electrical Characteristics in the Source and Drain Regions of Polycrystalline Silicon Based in One Transistor Dynamic Random Access Memory.

In this paper, we present a capacitorless one transistor dynamic random access memory (1T-DRAM) based on a polycrystalline silicon (poly-Si) double gate MOSFET with grain boundaries (GBs). Several studies have been conducted to implement 1T-DRAM using poly-Si. This is because poly-Si has the advantage of low-cost fabrication and can be stacked. However, poly-Si has GBs, which can adversely affect semiconductor device. So far, related studies on poly-Si-based 1T-DRAM have only focused on GBs present in the channel domain. Hence, in this study, we analyzed the transfer and memory characteristics when a GB is present in the source and drain regions. As a result, we found that in the center of the depletion region in the source and channel junction, where the effect of GB was most significant, sensing margins decreased the most from 0.88 to 0.29 μA/μm, and retention time (RT) decreased from 85 ms to 47 μs. In addition, we found that at the center of the depletion region in the drain and channel junction, where the effect of GBs was most significant in the drain region, RT decreased the most from 85 ms to 52 μs.

A new CASE for complementary materials science categorization

A new CASE for complementary materials science categorization

Antagonist effects of grain boundaries between the trapping process and the fast diffusion path in nickel bicrystals

Hydrogen-grain-boundaries interactions and their role in intergranular fracture are well accepted as one of the key features in understanding hydrogen embrittlement in a large variety of common engineer situations. These interactions implicate some fundamental processes classified as segregation, trapping and diffusion of the solute which can be studied as a function of grain boundary configuration. In the present study, we carried out an extensive analysis of four grain-boundaries based on the complementary of atomistic calculations and experimental data. We demonstrate that elastic deformation has an important contribution on the segregation energy which cannot be simply reduced to a volume change and need to consider the deviatoric part of strain. Additionally, some significant configurations of the segregation energy depend on the long-range elastic distortion and allows to rationalize the elastic contribution in three terms. By investigating the different energy barriers involved to reach all the segregation sites, the antagonist impact of grain boundaries on hydrogen diffusion and trapping process was elucidated. The segregation energy and migration energy are two fundamental parameters in order to classify the grain-boundaries as a trapping location or short circuit for diffusion.

Evading strength-corrosion tradeoff in Mg alloys via dense ultrafine twins

Conventional ultrafine-grains can generate high strength in Mg alloys, but significant tradeoff of corrosion resistance due to inclusion of a large number of non-equilibrium grain boundaries. Herein, an ultrafine-grain structure consisting of dense ultrafine twins is prepared, yielding a high strength up to 469 MPa and decreasing the corrosion rate by one order of magnitude. Generally, the formation of dense ultrafine twins in Mg alloys is rather difficult, but a carefully designed multi-directional compression treatment effectively stimulates twinning nucleation within twins and refines grain size down to 300 nm after 12-passes compressions. Grain-refinement by low-energy twins not only circumvents the detrimental effects of non-equilibrium grain boundaries on corrosion resistance, but also alters both the morphology and distribution of precipitates. Consequently, micro-galvanic corrosion tendency decreases, and severe localized corrosion is suppressed completely. This technique has a high commercial viability as it can be readily implemented in industrial production.

Effect of grain boundary direction on blistering in deuterium-exposed tungsten materials: Parallel grain boundary versus perpendicular grain boundary

The effect of grain boundary (GB) direction with respect to the exposed surface on blistering in tungsten (W) is studied. Four types of W materials were used in this work and classified according to GB directions: one with GBs parallel to the exposed surface (parallel GBs) and the other with GBs perpendicular to the exposed surface (perpendicular GBs). After exposure to high flux deuterium plasmas, blisters were observed and found to be related to GBs in all types of materials. It is found that large-size blisters were originated from parallel GBs rather than perpendicular GBs. Blisters were supposed to grow faster in parallel GBs than in perpendicular GBs. Moreover, the exfoliation of blister caps was observed in the materials with parallel GBs but not in that with perpendicular GBs. This study provides a new insight into the role of GB direction on blistering.

Effect of Crystallographic Orientation and Grain Boundaries on Martensitic Transformation and Superelastic Response of Oligocrystalline Fe\u2013Mn\u2013Al\u2013Ni Shape Memory Alloys

In situ tensile tests employing digital image correlation were conducted to study the martensitic transformation of oligocrystalline Fe–Mn–Al–Ni shape memory alloys in depth. The influence of different grain orientations, i.e., near-〈001〉 and near-〈101〉, as well as the influence of different grain boundary misorientations are in focus of the present work. The results reveal that the reversibility of the martensite strongly depends on the type of martensitic evolving, i.e., twinned or detwinned. Furthermore, it is shown that grain boundaries lead to stress concentrations and, thus, to formation of unfavored martensite variants. Moreover, some martensite plates seem to penetrate the grain boundaries resulting in a high degree of irreversibility in this area. However, after a stable microstructural configuration is established in direct vicinity of the grain boundary, the transformation begins inside the neighboring grains eventually leading to a sequential transformation of all grains involved.

Phase Field Modeling of Cubic to Tetragonal Transformation in YSZ and its Effect on Ionic Conductivity Degradation and Mechanical Damages

During the high-temperature operation of solid oxide fuel cells (SOFCs), the degradations of electrolyte material yttria-stabilized zirconia (YSZ) in both ionic conductivity and mechanical strength can be caused by the cubic to tetragonal phase transformation. In this work, microelasticity phase field model is built to simulate the YSZ phase transformation considering the effects of grain boundary and solid morphology. The YSZ skeleton in real SOFC anode is reconstructed using focused ion beam-scanning electron microscopy (FIB-SEM) dual-beam technique. The ionic conductivity degradation and the mechanical damages under external mechanical loads of brittle YSZ phase in anode are investigated based on the phase field simulation results. The simulation results may provide theoretical guidelines for improving the SOFC anode during fabrication.

Electrical properties of La-Mn-codoped BaTiO3-(Bi0.5Na0.5)TiO3 lead-free PTCR ceramics

La-Mn-codoped 0.97BaTiO3-0.03(Bi0.5Na0.5)TiO3 ceramics (abbreviated as xLa-yMn-BBNT3, x = 0.001, 0.002, 0.003, 0.004; y = 0, 0.0005, 0.001, 0.0015, 0.002) for application of lead-free positive temperature coefficient of resistivity (PTCR) thermistors were prepared using a wet chemical route. The analysis of XRD patterns shows that all prepared powders and ceramics are composed of pure tetragonal perovskite phase. The x = 0.002 La-doped ceramic sintered in air has a Curie temperature of Tc about 140 °C, room-temperature resistivity (ρ25) of ~103 Ω cm and resistivity jump (log(ρmax/ρmin)) of ~3 orders in magnitude. It is also found that the resistivity jump of prepared ceramic reaches up to 4.4 orders in magnitude when y = 0.0015 Mn was doped. Influence of grain and grain-boundary effect on PTCR effect was analyzed by complex impedance spectra measured at different temperatures, and the results reveal that the grain boundary effect plays key role in the PTCR effect.

Effects of temperature and grain size on active twinning systems in commercially pure titanium

In order to clarify the effects of grain boundary, grain size and deformation temperature on twinning deformation in polycrystalline commercially pure titanium, active twinning systems during compression deformation at temperatures from 25 °C to 800 °C investigated using SEM/EBSD techniques. Four twinning systems were confirmed to operate under compression at 10% strain in a deformation temperature dependent manner: {112̅1} and {112̅2} twins were observed only at relatively low temperatures (e.g. ≦ 400 °C), while, {101̅1} twins were observed at relatively high temperatures (e.g. ≧ 400 °C), and {101̅2} twins formed at every tested temperature (25 °C–800 °C). Our results suggested that the effects of strain concentration at grain boundaries on twinning differ based on the active twinning systems, which are affected by: 1) the difference in the formation temperature ranges between single-crystal and polycrystalline specimens, 2) the ratio of the number of deformation twins touching grain boundaries to the total number of deformation twins, and 3) grain size dependence.

Effect of Cr addition on the structure and electrical properties of CaCu3Ti4O12 NTC thermistor

In the present work, CaCu3-xCrxTi4O12 (CCCTO, 0 ≤ x ≤ 1) ceramics were prepared by a solid-state reaction. The influence of Cr on the structure and electrical properties of the CCCTO ceramics was investigated in detail. X-ray diffractometry (XRD) revealed that all samplesʼ main phases were CaCu3Ti4O12 (CCTO), but CuO and CaTiO3 phases were also found. Cr doping suppressed the abnormal growth of grains, thus the grain size distribution became more uniform with the increase of Cr doping content. The resistance-temperature analysis revealed that all CCCTO ceramics had a noticeable Negative Temperature Coefficient (NTC) effect. The resistivity ρ30 of the CCCTO ceramics decreased from 1.15 × 106 to 8.73 × 104 Ω cm with an increase in the value of x, along with a decrease in the thermal constant B from 6596 to 3267 K. It was also observed that both the grain and grain-boundary effects contributed to their NTC characteristics. The analysis revealed that the conductivity of the ceramics arose mainly from the electron hopping mechanism. All the samples showed an electrical relaxation behavior. The observations indicated that the structures and electrical properties of CCCTO ceramics could be attuned precisely by adjusting the concentration of the Cr2O3 doping agent.

Nanocrystalline strain glass TiNiPt and its superelastic behavior

TiNi-based shape-memory alloys are known to exhibit a strain glass state under certain conditions, generally in the presence of high-density defects such as excess solute atoms or alloying elements, dislocations, and nanoprecipitates. In this paper, we report a strain glass transition in a nanocrystalline ${\mathrm{Ti}}_{50}{\mathrm{Ni}}_{35}{\mathrm{Pt}}_{15}$ alloy. The nanocrystalline strain glass state is achieved by a combined effect of high-density grain boundaries and high concentration doping of Pt atoms in the B2 matrix. The nanocrystalline ${\mathrm{Ti}}_{50}{\mathrm{Ni}}_{35}{\mathrm{Pt}}_{15}$ strain glass alloy showed a large near-complete progressive superelasticity with a recovery strain of about 6% and a low apparent Young's modulus of about 30 GPa in a wide temperature range of over 200 \ifmmode^\circ\else\textdegree\fi{}C. In situ synchrotron x-ray diffraction measurement showed that the strain glass B2 [B2(SG)] phase experienced B2(SG)\ensuremath{\rightarrow}R\ensuremath{\rightarrow}B19 transformation upon loading and B19\ensuremath{\rightarrow}B2(SG) upon unloading. The findings of this study provide insight for the development of nanocrystalline strain glass shape-memory alloys.