Grain Boundary Migration Rate Research Articles

Effect of Ti content on abnormal grain growth of Fe–Mn–Al–Ni–Ti shape memory alloy

In this paper, the effects of Ti content on the solvus temperature of γ-phase and abnormal grain growth (AGG) in Fe43.5−x Mn34Al15Ni7.5Ti x (x = 0, 0.5, 1 and 1.5) shape memory alloys (SMAs) were investigated. It is found that, the increase of Ti content leads to a significant reduction of the solvus temperature of γ-phase, a significant refinement of γ-phase, and a decrease of subgrain size. After 3 times cyclic heat treatments, the average grain size of Fe42Mn34Al15Ni7.5Ti1.5 SMA reaches about 9.0 mm, which is about twice of that for Fe42.5Mn34Al15Ni7.5Ti1 SMA. This is attributed to the small subgrains can provide a higher subgrain boundary energy (ΔG s) and grain boundary (GB) migration rate. The subgrain size of Fe42Mn34Al15Ni7.5Ti1.5 SMA (9.7 μm) is significantly smaller than that of Fe42.5Mn34Al15Ni7.5Ti1 SMA (21.3 μm). Thereby, the ΔG s (15.3 × 10−2 J mol−1) and GB migration rate (11.3 × 10−6 m s−1) of Fe42Mn34Al15Ni7.5Ti1.5 SMA are significantly higher than those of Fe42.5Mn34Al15Ni7.5Ti1 SMA (7.1 × 10−2 J mol−1, 6.3 × 10−6 m s−1). In addition, when the applied strain was up to 10%, the maximum superelastic strain of Fe42Mn34Al15Ni7.5Ti1.5 and Fe42.5Mn34Al15Ni7.5Ti1 were 5.5% and 5.1%, respectively. In summary, the addition of 1.5 at.% Ti in Fe–Mn–Al–Ni–Ti SMA can promote the AGG with relatively small loss in superelasticity.

Effect of Calcium on the Rate of Grain Boundary Migration in Pure Magnesium During Annealing

Effect of Calcium on the Rate of Grain Boundary Migration in Pure Magnesium During Annealing

The effects of antimony and hot rolling on the microstructure, texture, and magnetic properties of a non-oriented electrical steel

The present work investigates the effects of antimony and hot rolling on the microstructure, texture, and magnetic properties of a 1.2 wt%Si electrical steel. For this purpose, three samples with 0.002, 0.012, and 0.026 wt% antimony were produced by melting in an induction furnace and casting into ingots, followed by hot rolling with a 75 % reduction. The aim was to better understand the interaction effects of adding antimony and hot rolling on the microstructure, texture, and magnetic properties. Microstructural studies were performed using optical microscopy (OM) and field emission scanning electron microscopy (FESEM). The macrotexture measurement was performed via X-ray diffraction (XRD), while magnetic properties were measured by a vibrating sample magnetometer (VSM). The results showed that increasing the antimony content gradually reduces the grain size, which is due to the effect of antimony on the migration rate of grain boundaries. This behavior was observed in both as-cast and hot-rolled samples. The texture in as-cast samples is random, and θ-fiber is observed after hot rolling. The examination of the texture parameter (TP) showed that the sample with 0.002 wt%Sb has a higher TP compared to other samples. Moreover, the lowest levels of coercivity and remanence are observed in this sample, which is due to the inverse relationship between the grain size and coercivity. The addition of antimony reduces the grain size, thus destroying the magnetic properties under these conditions.

Effects of sintering aids on microstructure, mechanical, and optical properties of AlON ceramics synthesized by SPS

AbstractAluminum oxynitride (AlON) ceramics doped with different sintering aids were synthesized by spark plasma sintering process. The microstructures, mechanical, and optical properties of the ceramics were investigated. The results indicate that the optimal amount of sintering aids is 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO. The addition of La3+ and Mg2+ decreases the rate of grain boundary migration in ceramics, promotes pore elimination, and inhibits grain growth. The addition of Y3+ facilitates liquid‐phase sintering of AlON ceramics. Moreover, the addition of Mg2+ effectively promotes twin formation in the ceramics, which hinders crack propagation and dislocation motion when the ceramics are loaded. Hence, the AlON ceramic doped with 0.06 wt% La2O3 + 0.16 wt% Y2O3 + 0.30 wt% MgO exhibits a relative density of 99.95%, an average grain size of 9.42 μm, and a twin boundary content of 10.3%, which contributes to its excellent mechanical and optical properties.

Influence of carbon and oxygen impurities on the migration rate of <110> tilt boundaries in austenite

The effect of impurity carbon and oxygen atoms on the migration rate of the tilt boundaries with the misorientation axis <110> in γ-Fe with fcc crystal lattice was studied by the method of molecular dynamics. Dependences of energy of the considered boundaries and rate of their migration at a temperature of 1600 K on the misorientation angle were obtained. The migration rate of <110> tilt boundaries under the same conditions turned out an order of magnitude lower than the migration rate of <111> and <100> boundaries, which is primarily due to the relatively low energy of <110> boundaries. In addition, the low-angle <110> tilt boundaries are unique compared to other tilt boundaries – grain­boundary dislocations in them are ordinary perfect edge dislocations with even cores that do not contain jogs periodically located on them as in <111> and <100> boundaries. The introduction of impurity carbon and oxygen atoms led to a significant decrease in migration rate of the grain boundaries. The binding energies of impurity carbon and oxygen atoms with grain-boundary dislocations in the austenite were calculated. The obtained values correlate well with the dependences of migration rate of <110> boundaries on the impurities concentration. Effect of impurities on migration of the boundaries in austenite turned out to be stronger than in the previously studied nickel and even more so in silver, which can be explained by the relatively low value of the electronegativity of iron atoms in comparison with nickel and silver. A higher value of the binding energy with dislocations in austenite and, accordingly, a greater effect on the migration rate of grain boundaries were obtained for carbon atoms.

Solute drag assessment of grain boundary migration in Au

Solute atoms segregate and impose a retarding pressure, also known as solute drag pressure, at the grain boundary (GB) leading to reduced GB migration rates. The solute drag pressure depends critically on the segregation energy and the solute diffusivity across the GB. These parameters are, however, typically used as adjustable parameters to describe experimental observations. Here, we present an approach to analyze solute drag based on density functional theory (DFT) calculations. As an example, we apply the proposed approach to available experimental data for migration rates of the 30∘<111> GB in Au with Fe and Bi impurities at the ppm level. Based on the DFT calculations, Bi is identified as a strongly segregating element while Fe segregation is weak in comparison. The effective segregation energy for Bi is found to vary from −0.59 eV to −0.72 eV in the experimentally investigated temperature range of 500–610 K. Further, the activation energy for trans−GB diffusion of Bi is calculated with DFT to fall into the range of 0.5–0.6 eV. These DFT based values are consistent with those obtained by the conventional solute drag analysis of the experimental data using the Cahn−Lücke−Stüwe (CLS) model. The proposed approach is discussed in terms of its strengths for trend predictions as well as its quantitative uncertainties.

Влияние концентрации вакансий на скорость миграции границ наклона в никеле: молекулярно-динамическое моделирование

The effect of vacancy concentration on the migration rate of high-angle tilt boundaries with misorientation axes &lt;111&gt; and &lt;100&gt; in nickel was studied by the method of molecular dynamics. It is shown that the dependence of the migration rate of grain boundaries on the vacancy concentration is nonmonotonic and has a maximum at a concentration of vacancies introduced at the initial stage of about 1%. With a further increase in concentration, especially above 4%, the migration rate of the considered boundaries decreased as a result of deceleration of boundaries by low-mobility vacancy clusters attached to it, which the boundary could no longer sorb, as in the case of relatively small clusters.

Recrystallization and Associated Twinning Evolution in Nickel-Based GH4141 Superalloy During Annealing

The GH4141 superalloy with 20, 40 and 55% cold deformations is annealed at 1080, 1120 and 1180 °C for 3-25 min to study the recrystallization and twinning behavior. The migration rate of grain boundaries increases significantly as the temperature increases in the range of 1080-1180 °C. After recrystallization, the hardness of the alloy is obviously reduced, and the recrystallized grains are randomly oriented without preferred orientation. The orientation imaging microscopy maps indicate that large amounts of Σ3 twin boundaries caused by the stacking faults appear in recrystallized grains. On one hand, the fraction of Σ3 boundaries after short time annealing has increased with the increase of temperature, meaning that the higher temperature contributes to the faster migration rate of grain boundaries and thus promotes the formation of stacking faults and twin boundaries before full recrystallization. On the other hand, the density of Σ3 boundaries has gradually decreased with the increase of grain size due to the annihilation and rare formation of twin boundaries after full recrystallization. The twinning evolution can be explained using the classical growth accident model.

Optimization of the grain boundary character distribution of pure copper by low-strain thermomechanical processing

Abstract Although thermomechanical processing has been widely used in grain boundary engineering, the relationship between thermomechanical parameters and grain boundary character distribution is still not well understood. In the present study, electron backscatter diffraction was used to study the grain boundary character distribution in pure copper after lowstrain thermomechanical treatments. It was found that the low-R coincidence site lattice frequency and grain size decreases in the following sequence, 10% compression &gt; 15% compression &gt; 5% compression, except for 700 0C. During thermomechanical treatments of copper, strain-induced grain boundary migration and grain growth may occur during annealing of 5% compressed copper, and recrystallization dominates during annealing of 15% compressed copper, while the annealing mechanism of 10% compressed copper changes from strain-induced grain boundary migration and grain growth to recrystallization when the annealing temperature exceeds 600 0C. The results indicated that during single-step low-strain thermomechanical treatments, straininduced grain boundary migration and grain growth would gradually change to recrystallization with the increase of pre-deformation level and annealing temperature. Among the three mechanisms, strain-induced grain boundary migration seems to be more effective than recrystallization and grain growth in the optimization of grain boundary character distribution, and it is suggested that this is due to the high boundary migration rate of strain-induced grain boundary migration.

Evolution of Annealing Twins and Recrystallization Texture in Thin-Walled Copper Tube During Heat Treatment

Thin-walled copper tubes are usually produced by multi-pass float-plug drawing deformation. In general, the annealing treatment subsequently is necessary to release the stored energy and adjusts the microstructure. In this study, an investigation on the evolution of annealing twins as well as textures in the thin-walled (Ф6 mm × 0.3 mm) copper tube underwent holding time-free heat treatment was reported. Electron backscattered diffraction analysis reveals that a large number of Σ3 boundaries (60° 〈111〉 twin relationship) are produced at the early stage of heat treatment, which is due to the lower boundary energy. With the recrystallization proceeding, the migration rate of grain boundaries decreases on account of the grain growth; meanwhile, the unique Σ9 boundaries (38.9° 〈110〉 relationship) are formed due to the interaction of the Σ3 boundaries. As a result, the number fractions of Σ3 boundaries and high-angle grain boundaries decrease rapidly. During the grain growth stage, a strong recrystallization texture was formed due to the fact that the grains of Goss orientation have a growth advantage over the others. As a result, the initial copper texture was transferred into the Goss texture in domination.

Fabrication and properties of in situ intergranular CaZrO3 modified microporous magnesia aggregates

Lightweight microporous magnesia aggregates with closed porosity of 6.2%, apparent porosity of 2.1% and median pore size of 2.36 μm were fabricated by introducing nano-sized ZrO2 combined with magnesite decomposition and sintered at 1780 °C. The sintering properties and microstructure revealed that nano-sized ZrO2 promoted the sintering and formation of closed intragranular pores by increasing abundant crystal defects and producing cation vacancies (VMg'') raising the migration rate of grain boundaries, which induced a change in porosity type from large open pores to small closed pores. The nano-sized ZrO2 changed the bonding of magnesia grains from single CaO–SiO2–MgO phases bonding to composited CaO–SiO2–MgO phases-CaZrO3 phases bonding, significantly enhancing the slag penetration resistance. The closed porosity played a more important role in reducing the thermal conductivity compared with total porosities. The microporous magnesia aggregates and thermal conductivity of 8.994 W (m K)−1 at 800 °C exhibit potential for application in wear lining refractories.

Effects of Cr addition on the constitutive equation and precipitated phases of copper alloy during hot deformation

The Cu-Ni-Si alloy has widely applications in the lead frames and electronics industries due to its high strength and conductivity. In this work, hot deformation behavior of the Cu-1.5Ni-1.1Co-0.6Si and Cu-1.5Ni-1.1Co-0.6Si-0.1Cr alloys were investigated through the isothermal compression tests using the Gleeble-1500D thermo-mechanical simulator operating at the temperature ranging from 500 °C to 900 °C and 0.001–10 s−1 strain rate. The deformed microstructure was characterized by the electron backscatter diffraction (EBSD) and the transmission electron microscopy. The constitutive equations of the alloys were established. According to the microstructure analysis, it can be observed that the grain size of the alloy with Cr was more uniform. In addition, the misorientation angle of 14.19 during recrystallization was significantly lower than 24 after the recrystallization, which means that the migration rate of grain boundaries is slow. The texture of the Cu-Ni-Co-Si alloy at 800 °C is the Goss {011}〈100〉 texture and {001}〈100〉 cubic texture, while the Goss texture at 900 °C is replaced by the {011} 〈112〉brass texture. The effects of Cr on precipitation phases were analyzed, and the precipitated phases were (Ni, Co)2Si, Co2Si. The addition of Cr promoted precipitation and significantly reduced the precipitate size. The addition of Cr can improve the strength and activation energy of the alloy. The activation energy was 569.8 kJ/mol and 639.5 kJ/mol, respectively.

Influence of phosphorus on hot deformation microstructure of a Ni-Fe-Cr based alloy

The influence of phosphorus on hot deformation microstructure of GH984G alloy was investigated. The results indicate that phosphorus accelerates the process of dynamic recrystallization (DRX) nucleation and prolongs the time of DRX grain growth. The alloy containing more phosphorus shows greater flow stress and dislocation density in the early stage of hot deformation, while the stress and dislocation density decrease with the increase of phosphorus after further deformation. Phosphorus inhibits the formation of Σ3 twin boundary at low strain rate or high deformation temperature but promotes it at high strain rate and low deformation temperature. The microstructure characterizations reveal that more blocky MC carbides with larger size form in the alloy with higher phosphorus content and serve as strong obstacles to the dislocation movement, thus increasing the flow stress and dislocation density in the early stage of hot deformation. The higher dislocation density promotes the nucleation of dynamic recrystallization and then reduces the flow stress and dislocation density at higher strain. The formation of Σ3 boundaries depends on growth accident during the process of DRX grain growth. More MC carbides in phosphorus-containing alloy decrease the rate of grain boundary migration and the frequency of growth accident, then reduce the fraction of Σ3 boundary. The change of twin boundary with phosphorus content at high strain rate and low deformation temperature is related to the critical grain size of twin formation.

Effect of recrystallization annealing temperature on texture and magnetic properties of 2.97% Si non-oriented silicon steel

The effect of recrystallization annealing at temperatures varying from 910 to 1060 °C on the texture and magnetic properties of cold-rolled sheets with 0.3 mm in thickness of 2.97 wt.% Si–0.59wt.% Al non-oriented silicon steel were investigated. With increasing of cold-rolled sheets annealing temperature, the average of the recrystallized grain sizes increased, because of higher temperature corresponds to a faster migration rate of grain boundaries. Increasing of grain size resulted in reducing of the hysteresis loss and core losses, as the number of grain boundary significantly reduced. However, the domain size and the eddy current loss would increase as the grain sizes continued to increase, and then affecting the core losses. The oversized microstructure (∼140 µm) in 1030 °C annealed sheet brought about an augment in P15/50 (∼2.27 W/kg) and (∼130 µm) in 1000 °C annealed sheet of P10/400 (∼12.84 W/kg). Furthermore, the textures of the final sheets were mainly made up of α*-fiber, γ-fiber and {001}&lt;130&gt; texture. The magnetic induction diminished with increasing of annealing temperature and this result could be attributed to the strengthening in γ-fiber (&lt;111&gt;//ND) and weakening in λ-fiber (&lt;100&gt;//ND) texture.

Effect of grain-boundary diffusion acceleration during recrystallization in submicrocrystalline metals and alloys prepared by severe plastic deformation

The results of studying the effect of grain-boundary diffusion acceleration during the annealing of submicrocrystalline (SMC) materials prepared by severe plastic deformation techniques are described. It is shown that the grain-boundary diffusion coefficient during recrystallization of SMC materials depends on the density of lattice dislocations and the pattern and rate of migration of the grain boundaries. It is found that, in SMC metals that undergo anomalous grain growth during annealing, the grain-boundary diffusion coefficient increases and its activation energy decreases. In SMC materials in which the recrystallization process exhibits conventional behavior, the diffusion properties of grain boundaries hardly differ from the equilibrium properties. Expressions describing the dependence of the grain-boundary diffusion coefficient on the migration rate of grain boundaries, as well as the thermodynamic and crystallographic parameters of the material, are derived. The calculation results are compared with the experimental data.

New insight into the mechanism of metadynamic softening in austenite

In the current study, the relation between the softening behaviour and the grain structure, dislocation substructure and crystallographic texture development was investigated during post-deformation annealing of a fully dynamically recrystallized (DRX) austenitic Ni–30%Fe model alloy. The present observations revealed a novel mechanism of post-dynamic softening consisting of several concurrent processes. The initial softening stage involves rapid growth of the dynamically formed nuclei and migration of the mobile boundaries. Simultaneously, the sub-boundaries within DRX grains progressively disintegrate through dislocation climb and dislocation annihilation. This eventually leads to the formation of dislocation-free grains, and reduction in the rate of grain boundary migration. As a result, the DRX texture largely remains preserved throughout the annealing process. Furthermore, the visibility of extrinsic grain/twin boundary dislocations, originated from absorbed glide lattice dislocations during the DRX process, gradually decreases during the post-deformation annealing, as a result of their mutual annihilation and progressive incorporation into the boundary structure.

Multi-Phase-Field Model to Simulate Microstructure Evolutions during Dynamic Recrystallization

A numerical model to simulate microstructure evolution and macroscopic mechanical behavior during hot working was developed. In this model, we employed a multi-phase-field model to simulate the growth of dynamically recrystallized grains with high accuracy and the Kocks-Meching model to calculate the evolution of dislocation density due to plastic deformation and dynamic recovery. Furthermore, an efficient computational algorithm was introduced to perform the multi-phase-field simulation efficiently. The accuracy of the developed model was confirmed by comparing the migration rate of grain boundaries with the theoretical value. Also, the numerical results for a polycrystalline material are compared with those obtained from a cellular automaton simulation. Furthermore, the effects of the initial grain size, grain boundary mobility and nucleation rate on the dynamic recrystallization behavior were investigated using the developed model.

In Situ EBSP Analysis of Grain Boundary Migration during Recrystallization in Pure Aluminum Foils

Grain boundary mobility in preferential growth of cube grains ({100}&lt;001&gt;) was evaluated by in-situ electron back scattering diffraction pattern (EBSP) analysis in order to clarify the fundamental mechanism of primary recrystallization in pure aluminum foils of 99.9% purity thermo-mechanically processed in the industrial production route for aluminum foils for electrolytic capacitors. We have carried out the continuous EBSP measurements during recrystallization of the aluminum foils heated to various temperatures in the chamber of scanning electron microscopy (SEM). We have succeeded in dynamic observation of the preferential growth of cube grains by the in-situ EBSP analysis. The in-situ EBSP analysis could reveal the migration rate of grain boundaries surrounding the cube grains. It was clarified that the proportional relation between migration rate and annealing time was satisfied. The stored energy providing the driving force for the grain boundary migration during primary recrystallization could be estimated from the misorientation within the deformed grains. The mobility of the grain boundary could be evaluated using the measured grain boundary migration rate and stored energy. Then the activation energy could be estimated by the in-situ EBSP analysis at various temperatures ranging from 270°C to 310°C. The obtained activation energy was 124 kJ/mol, which approximately corresponded to that for the diffusion of impurity such as iron or silicon in aluminum. This suggested that the rate-determining process of the grain boundary migration of cube grains was impurity diffusion in the pure aluminum foils.

Atomic motion during the migration of general [0 0 1] tilt grain boundaries in Ni

We generalize a previous study of the atomic motions governing grain boundary migration to consider arbitrary misorientations of [001] tilt boundaries. Our examination of the nature of atomic motions employed three statistical measures of atomic motion: the non-Gaussian parameter, the “dynamic entropy” and the van Hove correlation function. These metrics were previously shown to provide a useful characterization of atomic motions both in glass-forming liquids and strained polycrystalline materials. As before, we find highly cooperative, string-like motion of atoms, but the grain boundary migration itself is a longer timescale process in which atoms move across the grain boundary. These observations are consistent with our previous results for Σ5 [001] tilt boundaries. It is evident from our work that the grain boundary structure and misorientation have a significant influence on the rate of grain boundary migration.

The effect of starting nanostructure on the thermal stability of electrodeposited nanocrystalline Co

The effect of starting microstructure on the thermal stability of electrodeposited nanocrystalline Co was studied. The starting microstructure was characterized by X-ray diffraction, transmission electron microscopy, and infrared spectroscopy, while the thermal stability was investigated by differential scanning calorimetry. It was found that over the range of starting structures examined, 8–20 nm mean grain size and 240–980 ppm S, the S impurities have the dominant effect on the thermal stability. It was determined that the rate of abnormal grain boundary migration was controlled by dynamic segregation.