Effect Of Grain Boundary Characteristics Research Articles

Deciphering the effect of grain boundary characteristics on fracture toughness of silicon nitride ceramics through a CNN regression model

Fracture toughness of silicon nitride (Si3N4) ceramics with different grain boundary characteristics was determined from their microstructural images via a convolutional neural network (CNN) model. For this purpose, the CNN model was trained using Si3N4 ceramics with sintering additives of Y2O3 and MgO, and then the fracture toughness for those with various lanthanoid oxides and MgO was determined from the microstructural images through the trained model. Herein, the difference between the determined and measured values indicates the effect of the grain boundary characteristics because they little appear in the microstructures. The measured and AI-determined fracture toughness showed that the large ionic radius of Sm2O3 enhanced the fracture toughness of the Si3N4 ceramics sintered at 1850 °C for 24 h. The trained model successfully determined fracture toughness values that closely matched the measured ones from the microstructural images, even for samples with pores and different grain boundary characteristics, except for the Sm2O3 sample sintered for 24 h.

Effects of grain boundary characteristics changing with cold rolling deformation on intergranular corrosion resistance of 443 ultra-pure ferritic stainless steel

The relationship between evolution in grain boundary characteristics and intergranular corrosion properties of cold rolled 443 ultra-pure ferritic stainless steel was investigated. The results showed that low-angle (LA) grain boundaries, special grain boundaries (SGB), and high-angle (HA) grain boundaries had a high intergranular corrosion sensitivity after cold deformation in reducing acid medium. In oxidative acid medium, the LA and SGB boundaries had a high intergranular corrosion resistance in comparison to HA boundaries, and their inhibitory effect on the corrosion continuance of the dynamic recrystallization high-angle (RHA) grain boundaries can improve the corrosion resistance of the RHA grain boundaries.

Effects of Grain Boundary Characteristics on Secondary Recrystallization Textures in Fe–Si Alloy

Effects of Grain Boundary Characteristics on Secondary Recrystallization Textures in Fe–Si Alloy

A computational framework for predicting the fracture toughness of metals as function of microstructure

We present a simplified computational framework based on the cohesive finite element method (CFEM) for predicting the macroscale fracture measures such as KIC and JIC of ductile metals as functions of microstructural attributes. Currently, no systematic approach exists to explicitly quantify the effects of grain and grain boundary behavior on the fracture measures of polycrystalline materials. Our computational approach involves embedding a microstructure region around the crack tip in a compact tension specimen subjected to mode-I loading and explicitly resolving fracture processes in the microstructure. To track how the interplay between intergranular and transgranular fracture mechanisms affect the fracture processes and consequently KIC and JIC, a grain boundary misorientation dependent interfacial separation model is used. The framework allows exploration of the effects of microstructure on the macroscopic fracture measures via the manifestation of different fracture mechanisms. Calculations carried out for Mo capture and delineate the competing effects between (a) intergranular and transgranular fracture and (b) constituent plasticity and fracture on the overall fracture toughness of the material. The use of statistically equivalent microstructure sample sets (SEMSS) allows the statistical distributions of KIC to be predicted for Mo with different grain sizes. The results indicate that, as the minimum grain boundary interfacial strength decreases and the grain yield strength increases, intergranular fracture becomes more pronounced over transgranular fracture. Consequently, the plastic dissipation primarily associated with transgranular fracture is suppressed, resulting in lower overall fracture toughness. Microstructures with intermediate levels of grain size exhibit the toughest material response via a combination of tortuous crack paths and plastic dissipation. Finally, the results are analytically quantified in a manner that takes into account the effects of grain boundary characteristics, constituent plasticity, and stochasticity via the use of the SEMSS. Although the calculations here are performed on Mo in a simplified setting, the approach can be extended and applied to other material systems.

Effects of Grain Boundary Characteristics on Its Capability to Trap Point Defects in Tungsten**Supported by the National Natural Science Foundation of China under Grant Nos 91426301, 11605256 and 11405231.

As recombination centers of vacancies (Vs) and self-interstitial atoms (SIAs), firstly grain boundaries (GBs) should have strong capability of trapping point defects. In this study, abilities to trap Vs and SIAs of eight symmetric tilt GBs in tungsten are investigated through first-principles calculations. On the one hand, vacancy formation energyrapidly increases then slowly decreases as the hard-sphere radius r0of the vacancy increases. The value ofis the largest when r0is about 1.38 Å, which is half the distance between the nearest atoms in equilibrium single crystal tungsten. That is, any denser or looser atomic configuration around GBs than that in bulk is helpful to form a vacancy. On the other hand, SIA formation energyat GBs decreases monotonically with increasing the hard-sphere radius of the interstitial sites, which indicates that GBs with larger interstitial sites have stronger ability to trap SIAs. Based on the data obtained for GBs investigated in this study, it is found that the ability to trap Vs increases as the GB energy increases, and the capability of trapping SIAs linearly increases as the excess volume of GB increases. Due to its lowest GB energy and smallest excess volume among all GBs studied, twin GB ∑3(110)[111] has the weakest capability to trap both Vs and SIAs.

Impact of grain boundary characteristics on lattice thermal conductivity: A kinetic theory study on ZnO

Grain boundaries are natural interfaces present in polycrystalline materials and have an important role in transport properties. In this work, the impact of grain boundary crystallographic mismatch, local impurity modulation, and spacing on lattice thermal conductivity is examined from the kinetic theory approach, with ZnO as a case study. We employ a dislocation-based model to describe the grain boundary scatterings of phonons, in which structural characteristics of grain boundaries are explicitly built-in and grain boundary scattering time depends on phonon frequency. This is in contrast to the gray model or the commonly used Casimir limit, which is blind to both grain boundary features and phonon frequency. We show that the lattice thermal conductivity generally decreases with grain boundary misorientation angle, and this dependence is significant for small grain boundary spacing while it tends to diminish for a large one. Intriguingly, our results show that local grain boundary chemistry can affect even more substantially than the crystallographic misfit on phonon relaxation time and interfacial thermal (Kapitza) resistance. Our results suggest new opportunities in tuning lattice thermal conductivity besides the nanostructure engineering approach, and demonstrates the synergetic effects of grain boundary characteristics on phonon conduction in polycrystals.

Microstructural evolution of a fine-grained 7075Al alloy processed by friction stir process during partial remelting

The success of thixoforming mostly depends on the preparation of semisolid slurry, consisting of non-dendritic and spherical solid grains surrounded by liquid. Initial microstructure of alloys before remelting, especially the initial grain size and the grain boundaries, can influence microstructural coarsening of semisolid alloys. The investigation focused on the microstructural evolution during reheating of a fine-grained 7075Al alloy processed by friction stir process (FSP) into the semisolid state. The results showed that a semisolid slurry containing fine and spherical solid grains was prepared and the distribution of solid grains and liquid phase is relatively uniform. Owing to the penetration of liquid phase into high angle grain boundaries (HAGBs) and a large fraction of HAGBs in the FSPed alloy, a network structure of intragranular liquid film in the semisolid state can be obtained in a short soaking time. The coarsening rate constant of the alloy increased with increasing liquid fraction. The grain coarsening mechanism in the semisolid state was discussed, and the effect of grain boundary characteristics in the initial microstructure on coarsening kinetics of semisolid alloys was also described.

The effect of grain boundary characteristics on the morphology of the crystal/melt interface of multicrystalline silicon

The effect of grain boundary characteristics on the crystal/melt interface morphology during the unidirectional solidification of multicrystalline Si was studied by in situ observations. It was shown that sharp and smooth grooves were formed at the crystal/melt interfaces at Σ27 and random grain boundaries, whereas no grooves were formed at Σ3 {1 1 1} twin boundaries. We explain the reasons why the grooves form at grain boundaries and discuss the impurity segregation at the grain boundary grooves on the crystal/melt interface.

Effect of grain boundary characteristics on the oxidation behavior of ferritic stainless steel

The effect of grain boundary characteristics on the oxidation of ferritic stainless steel was investigated using XRD, SEM, energy dispersive spectroscopy, and electron backscattered diffraction. Oxide crystals at special grain boundaries were compared with that of random boundaries. The spinel type oxide grew along the grain boundaries whereas both spinel and chromia grew at the grain interiors. Oxidation rate at special boundaries was slower than random boundaries. The resistance to oxidation of special boundaries is influenced by their angular deviation from the ideal coincidence site lattice (CSL) misorientation. The special boundaries near ideal CSL misorientation are more resistant to oxidation.

Integrated Effects of Grain Boundary Characteristics on the Behavior of Intergranular Corrosion in 5XXX-Series Alloys

not Available.

Effect of Grain Boundary Characteristics on Lattice Orientations

Grain boundary characteristics are defined by five parameter, grain boundary plane normal and misorientation angle/axis between two adjacent grains. The influence of the grain boundary character distribution on lattice evolution during deformation was investigated using three-dimensional crystal plasticity finite element method (CPFEM). Various combinations of grain boundaries were modeled systematically. In analyzing the numerical microstructural characterization obtained by the simulation, orientation average scheme and correlation parameters between misorientation and its special distribution are used. Inter- and intra-grain structures were investigated using the spatial distribution of lattice orientation. Main emphasis was placed on misorientation distributions around grain boundaries, where grain interaction mainly occurred.

Effect of grain boundary characteristics on hot tearing in directional solidification of superalloys

The effect of grain boundary (GB) misorientation on hot tearing susceptibility of directionally solidified (DS) nickel-based superalloys was explored. We found that the castability of second generation nickel-based superalloy CMSX-4 is inferior to DS superalloy IN792, an alloy well known for bad castability. The castability of CMSX-4 is somewhat improved at a higher solidification rate. The hot tearing tendency increases with increasing GB misorientation angle. As feeding tendency becomes greater with increasing misorientation, this points to the importance of GB cohesion for solidification cracking in the alloy. Microstructure investigation reveals that hot tearing is associated with formation of continuous gamma and gamma prime eutectic films at the GB in CMSX-4. We assume that the gamma and gamma prime eutectic, which reflects the remaining liquid at the end of solidification, prevents the impinging dendrite arms from touching and in this way decreases cohesion.

Effect of grain-boundary characteristics on castability of nickel-base superalloys

Hot tearing susceptibility of two Ni-base superalloys, IN792 and CM247, during directional solidification was studied. Effects of grain-boundary (GB) misorientation on castability were examined by casting single-crystal (SC) and bicrystal (BC) specimens. Crack-free specimens were obtained in castings with GB misorientation angles of less than ∼12 deg. Severe cracking occurred if the GB angle was greater than 25 deg. Secondary dendrite arm length right at the GB was found to be larger than in the GB vicinity and to increase with GB misorientation. The amount of eutectic melt and foreign element segregation is also larger at the GB. The greater susceptibility of the GB to hot tearing is almost certainly caused by reduced strength compared to the grain interior. The reduced strength is either due to reduced secondary arm bridging because of geometrical constraints or due to the existence of a thin liquid film as a result of stronger segregation.

The Effect of Grain Boundary Characteristics on Microstructure and Stress Void Evolution in Electroplated and Sputtered Cu Films

The Effect of Grain Boundary Characteristics on Microstructure and Stress Void Evolution in Electroplated and Sputtered Cu Films

Correspondence

The success of thixoforming mostly depends on the preparation of semisolid slurry, consisting of non-dendritic and spherical solid grains surrounded by liquid. Initial microstructure of alloys before remelting, especially the initial grain size and the grain boundaries, can influence microstructural coarsening of semisolid alloys. The investigation focused on the microstructural evolution during reheating of a fine-grained 7075Al alloy processed by friction stir process (FSP) into the semisolid state. The results showed that a semisolid slurry containing fine and spherical solid grains was prepared and the distribution of solid grains and liquid phase is relatively uniform. Owing to the penetration of liquid phase into high angle grain boundaries (HAGBs) and a large fraction of HAGBs in the FSPed alloy, a network structure of intragranular liquid film in the semisolid state can be obtained in a short soaking time. The coarsening rate constant of the alloy increased with increasing liquid fraction. The grain coarsening mechanism in the semisolid state was discussed, and the effect of grain boundary characteristics in the initial microstructure on coarsening kinetics of semisolid alloys was also described.

Effect of grain boundary characteristics on mechanical behaviour of quenched aluminium

Tests concerning the mechanical properties of quenched aluminium were carried out on samples having different grain boundary characteristics. In comparison with aluminium of equilibrium structure, the quenched aluminium was found to be characterised by: a greater value of yield point in samples having a low fraction of special grain boundaries, and a lower value of yield point and a reduction of the Lüders strain in samples having a high fraction of special grain boundaries. The effects can be ascribed to the activity of dislocation loops as sources of dislocations or to a change in grain boundary characteristics as a result of annihilation of non-equilibrium vacancies on the grain boundaries.MST/965

Effect of grain boundary characteristics on mechanical behaviour of quenched aluminium

Tests concerning the mechanical properties of quenched aluminium were carried out on samples having different grain boundary characteristics. In comparison with aluminium of equilibrium structure, the quenched aluminium was found to be characterised by: a greater value of yield point in samples having a low fraction of special grain boundaries, and a lower value of yield point and a reduction of the Lüders strain in samples having a high fraction of special grain boundaries. The effects can be ascribed to the activity of dislocation loops as sources of dislocations or to a change in grain boundary characteristics as a result of annihilation of non-equilibrium vacancies on the grain boundaries.MST/965

Effects of Grain Boundary Characteristics of Steel on Magnetoacoustic Emission Spectra

AbstractThe pulse height distribution of a magnetoacoustic emission (MAE) spectrum is expected to be generally Gaussian due to its random nature. The functional form of distribution depends on the microstructure of a ferromagnet since the domain wall-lattice defect interaction produces MAE. The present study investigated the effects of grain boundary characteristics on the properties of MAE spectra obtained by external AC magnetic field-driven domain wall motions. The results show the enhancement of domain wall-defect interaction as more grain boundary disorder is introduced to HY80 steel samples. This was confirmed by the growth of a non-Gaussian-like distribution in the tail section of histograms with increased population of impurities trapped at the grain boundaries causing embrittlement. It is found that the enhancement of domain wall-defect interaction, which is responsible for generation of high amplitude MAE pulses, also tends to reduce the rate of such MAE events by limiting domain wall motions. Application of a stronger AC magnetic field should increase the count rate of high amplitude MAE signals in more embrittled samples.