Mechanism Of Grain Research Articles

Simulation of recrystallization grain growth in AZ61 magnesium alloy based on GA and 3D CA

In this paper, the Arrhenius constitutive model (GA-Arrhenius) optimized by genetic algorithm (GA) is established, and the dynamic recrystallization (DRX) grain growth process of AZ61 magnesium alloy during hot deformation is simulated by three-dimensional cellular automata (3D CA), and the morphological evolution and grain boundary migration of recrystallized grains are reproduced. The results show that the GA-Arrhenius model accurately predicts the rheological behavior of the material, while the 3D CA model effectively describes the formation and growth mechanism of grains during DRX.

Genome-Wide Identification of microRNAs Associated with Starch Biosynthesis and Endosperm Development in Foxtail Millet.

Foxtail millet is one of the oldest crops, and its endosperm contains up to 70% of starch. Grain filling is an important starch accumulation process associated with foxtail millet yield and quality. However, the molecular mechanisms of grain filling in foxtail millet are relatively unclear. Here, we investigate the genes and regulated miRNAs associated with starch synthesis and metabolism in foxtail millet using high-throughput small RNA, mRNA and degradome sequencing. The regulation of starch synthesis and quality is carried out mainly at the 15 DAA to 35 DAA stage during grain filling. The DEGs between waxy and non-waxy foxtail millet were significant, especially for GBSS. Additionally, ptc-miR169i_R+2_1ss21GA, fve-miR396e_L-1R+1, mtr-miR162 and PC-5p-221_23413 regulate the expression of genes associated with the starch synthesis pathway in foxtail millet. This study provides new insights into the molecular mechanisms of starch synthesis and quality formation in foxtail millet.

Inhibition of microelement accumulation and disorder of saccharide and amino acid metabolism explain rice grain empty under dimethylarsinic acid stress.

Metabolomic and transcriptomic analyses revealed an intensification of energy metabolism in rice grains under DMA stress, possibly causing the consumption of sugars or non-sugars and the development of unfilled grains Excessive dimethylarsinic acid (DMA) causes rice straighthead disease, a physiological disorder typically with erect panicle due to empty grain at maturity. Although the toxicity of DMA and its uptake and transport in rice are well recognized, the underlying mechanism of unfilled grains remains unclear. Therefore, a pot experiment was conducted using a susceptible variety (Ruanhuayou1179, RHY) and a resistant one (Nanjingxiangzhan, NJXZ) via the metabolomic and transcriptomic approaches to explore the mechanisms of empty grains in diseased rice under DMA stress. The results demonstrate an increase in total and methylated As in grains of RHY and NJXZ under DMA addition, with RHY containing higher levels of DMA. DMA addition increased the soluble sugar content in grains of RHY and NJXZ by 17.1% and 14.3% compared to the control, respectively, but significantly reduced the levels of amino acid, soluble protein, and starch. The decrease of grain Zn and B contents was also observed, and inadequate Zn might be a key factor limiting rice grain yield under DMA stress. Notably, DMA addition altered the expression levels of genes involved in the transport of sugar, amino acids, nitrates/peptides, and mineral ions. In sugar and amino acid metabolism, the reduction of metabolites and the upregulated expression of genes reflect positive regulation at the level of energy metabolism, implying that the reduction of grain starch and proteins might be ascribed to generate sufficient energy to resist the stress. This study provides a useful reference for understanding the molecular mechanism of grain emptying under DMA stress.

An experimental study of the effect of Ag, Cu, Li, Mg, Ni, Ti, Sc, Zr on grain refining in binary and multicomponent Al-based alloys

The objective of the current work is to establish the conventional mechanisms of grain refining, and the effect of the refiner-modifier interaction in Al-based alloys on the resultant grain refining obtained. The different castings were carried out in preheated metallic molds with solidification rates of around 0.15 °C/s and 7 °C/s. As the nucleation sites (Al3Ti) change in composition depending on the percentage of Si in the alloy, the term “poisoning” frequently used to explain the loss or weakening of the power of the refiner, is misused. Addition of L12 metals e.g., Zr and Sc would contribute to constitutional undercooling, restricting the coarsening of α-Al grains as well as act as suitable sites for heterogeneous nucleation. The use of transition or ultra pure (99.99) metals would increase the degree of undercooling as well as nucleation of new grains due to precipitation of the second phase leading to the formation of a heterogeneous grain distribution. Thus, grain refining of binary alloys - partially or fully, may not be produced only through constitutional undercooling. It is suggested that, the use of 0.18%Sc has more-or-less the same grain refining efficiency of 0.15%Ti added in the form of Al–Ti–B master alloy i.e., reduction in the grain size by about 85% and an increase in the alloy strength by about 30%. For a given solidification rate, there is a grain refining threshold beyond which no further refining can be achieved. Apparently grain refining mechanisms are independent of solidification rate, only the extent of refining.

Heterogenous Grain Nucleation in Al-Si Alloys: Types of Nucleant Inoculation

The objective of the current work is to establish, on the one hand, the conventional mechanisms of grain refining and, on the other hand, the effect of the refining-modification interaction in Sr-modified Al-Si alloys on the achieved grain refining and the modification of eutectic silicon. For this purpose, the hypereutectic alloy A390.1 (~17%Si) was used. Various grain refiners were used, namely, Al-10%Ti, Al-5%Ti-1%B, and Al-4%B. After the preparation of the liquid metal, several concentrations of these master alloys were added to the liquid bath according to the desired objective. The different melts prepared were heated at 750 °C and cast in a preheated graphite mold with a solidification rate of around 0.8 °C/s. The liquid metal was. The presence of strontium (added in the form of Al-10%Sr master alloy) and boron completely affects the microstructure of the alloy. An atom of Sr unites with 6 atoms of B to form a compound whose stoichiometric formula is of the SrB6 type, leading to a significant reduction in the modification. A strong relationship exists between the addition of B and the recovery level of Sr. The affinity between titanium and boron is stronger than the affinity between boron and strontium. Both B and TiB2 phase particles do not react with Si; it is only the Ti part of the Al-Ti-B master that forms (Al, Si)3Ti. Regardless of the amount of Si content in the alloy, the Al-4%B master alloy achieves the best grain refining compared to Ti-containing master alloys.

Resistance mechanisms of cereal plants and rhizosphere soil microbial communities to chromium stress.

Agricultural soils contaminated with heavy metals poison crops and disturb the normal functioning of rhizosphere microbial communities. Different crops and rhizosphere microbial communities exhibit different heavy metal resistance mechanisms. Here, indoor pot studies were used to assess the mechanisms of grain and soil rhizosphere microbial communities on chromium (Cr) stress. Millet grain variety 'Jingu 21' (Setaria italica) and soil samples were collected prior to control (CK), 6 hours after (Cr_6h), and 6 days following (Cr_6d) Cr stress. Transcriptomic analysis, high-throughput sequencing and quantitative polymerase chain reaction (qPCR) were used for sample determination and data analysis. Cr stress inhibited the expression of genes related to cell division, and photosynthesis in grain plants while stimulating the expression of genes related to DNA replication and repair, in addition to plant defense systems resist Cr stress. In response to chromium stress, rhizosphere soil bacterial and fungal community compositions and diversity changed significantly (p<0.05). Both bacterial and fungal co-occurrence networks primarily comprised positively correlated edges that would serve to increase community stability. However, bacterial community networks were larger than fungal community networks and were more tightly connected and less modular than fungal networks. The abundances of C/N functional genes exhibited increasing trends with increased Cr exposure. Overall, these results suggest that Cr stress primarily prevented cereal seedlings from completing photosynthesis, cell division, and proliferation while simultaneously triggering plant defense mechanisms to resist the toxic effects of Cr. Soil bacterial and fungal populations exhibited diverse response traits, community-assembly mechanisms, and increased expression of functional genes related to carbon and nitrogen cycling, all of which are likely related to microbial survival during Cr stress. This study provides new insights into resistance mechanisms, microbial community structures, and mechanisms of C/N functional genes responses in cereal plants to heavy metal contaminated agricultural soils. Portions of this text were previously published as part of a preprint (https://www.researchsquare.com/article/rs-2891904/v1).

A crystal plasticity-based microdamage model and its application on the tensile failure process analysis of 7075 aluminum alloy

In this study, a microdamage model by introducing the damage of crystal is proposed. Damage variables are defined for each slip system, and the damage-coupled crystal plasticity constitutive equations are derived by virtue of the concept of effective stress and the hypothesis of strain equivalence. A function of damage driving force is proposed by analyzing failure mechanisms. The damage evolution equation is then derived based on thermodynamics. After that, a differential evolution-based method is adopted for the calibration of the parameters, and a numerical simulation algorithm is implemented for the failure process simulation of a single crystal material for verification purposes. The proposed model and the corresponding numerical method are then applied to the failure process analysis of a polycrystalline material 7075 aluminum alloy. The EBSD observation is conducted to obtain the size and orientation of grains, which combines with the Voronoi diagram method to be the basis for establishing the polycrystal finite element model. Afterwards, the numerical simulation of the failure process of specimens under tension is conducted. The predicted results are in good agreement with the experimental observations. It indicates that the proposed model can well reflect the damage-softening effect from the microplasticity to the macroscopic deformation. Finally, the two damage mechanisms of grains in 7075 aluminum alloy are investigated based on the calculated result.

In-Situ Synchrotron HEXRD Study on the Micro-Stress Evolution Behavior of a Superalloy during Room-Temperature Compression.

The residual stress generated during heat treatment of nickel-base superalloys will affect their service performance and introduce primary cracks. In a component with high residual stress, a tiny amount of plastic deformation at room temperature can release the stress to a certain extent. However, the stress-releasing mechanism is still unclear. In the present study, the micro-mechanical behavior of the FGH96 nickel-base superalloy during room temperature compression was studied using in situ synchrotron radiation high-energy X-ray diffraction. The in situ evolution of the lattice strain was observed during deformation. The stress distribution mechanism of grains and phases with different orientations was clarified. The results show that at the elastic deformation stage, the (200) lattice plane of γ' phase bears more stress after the stress reaches 900 MPa. When the stress exceeds 1160 MPa, the load is redistributed to the grains with their <200> crystal directions aligned with the loading direction. After yielding, the γ' phase still bears the main stress.

Analysis of the formation mechanism of ceramic grains and mechanical properties of Mo2FeB2-based cermets by valence electron structure

The valence electron structures (VES) of Mo2FeB2-based cermets were constructed based on the empirical electron theory of solids and molecules (EET). The formation mechanism of grains and the influence of grain morphologies on the mechanical properties of the materials were explained in accordance with the calculated phase structure formation factors (S') and the interface electron structure (σN: the number of atom state groups, ∆ρ': electron density difference, and ρ': electron density), respectively. The results indicated that the morphologies of the Mo2FeB2 hard phase grains were reflected by the S' value of the distinct crystal planes. The progressive decrease in the Mo/B atomic ratio aggravated the differences between the S(210)' and S(001)' values and promoted the preferential growth of the hard phase grains along the [001] direction. This resulted in an increase in the (210)/(100) interface area, with the grains gradually forming an elongated structure. However, it was noticed that as the ratio of Mo to B increased, the value of |S(210)' − S(001)'| gradually tended toward 0, which allowed the elongated hard phase grains to transform into quasi-equiaxial grains. In addition, the maximum decrease in the σN value recorded was over 2500 when the Mo to B ratio increased continuously, indicating that the bonding strength at the (210)/(100) interface between the hard and binder phases was better at low Mo/B atomic ratios than at high Mo/B atomic ratios. This helped improve the fracture toughness and transverse rupture strength of the Mo2FeB2-based cermets.

Research of the process of air separation of grain material in a vertical zigzag channel

The aim of the research is to determine ways to improve the efficiency of grain materials pneumatic separation based on the study of the interaction mechanism of grains with the air flow in the channel elements, which are inclined sections of the air duct. The paper considers a modified separation method that separates the grain material according to the aerodynamic properties of the components in a vertical zigzag air channel in an aerodynamic and gravitational field. The studies were carried out by means of mathematical modeling followed by experimental confirmation of the modeling results. A computer mathematical model was created in the MathCad 13 application package to determine the parameters of the zigzag aspiration channel. This model describes the influx of parameters in the channel (width, height, cut of the zigzag ledge to the horizon, edge of the zigzag ledge) on the nature of the grain trajectory. As a result of the numerical simulation process using the mathematical package Mathematica, dependence was obtained to determine the trajectory of motion depending on the angular velocity. An increase in the pneumatic separation effect during the grain mixtures division due to the influence of the Magnus effect was established as a result of experimental studies. The design of a zigzag separator with an annular channel section has been improved based of the research carried out.

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.

Effect of target grain size on target sputter etching morphology and performance

In this paper, three large scalar high-purity solid copper targets with different grain sizes are sputtered under the same experimental conditions. The sputter etching mechanism of grains on the target surface and the influence of target grain size on the sputter etching morphology were observed. Moreover, the target voltage of the three targets has also been measured. The results reveal that the sputtering of the grain on the target surface is extending from the grain boundary to the grain interior. Targets with different grain sizes show different target voltages depending on the sputter etching morphology. The target with a small grain size has a uniform and dense morphology with connected pits and bulges and a slight “black slump.” This morphology renders a higher target voltage than ones with larger grain sizes, which is due to the recapture of secondary electrons on the surface of the target.

Comparative transcriptome analysis provides insights into grain filling commonalities and differences between foxtail millet [Setaria italica (L.) P. Beauv.] varieties with different panicle types.

Grain filling affects grain weight and quality and is among the most critical factors in determining the yield and quality of cereal crops. Though hybrids have larger panicles and numerous spikelets with a larger sink capacity than conventional varieties, data on the grain filling commonalities and differences between foxtail millet varieties with different panicle types remain sparse. In this study, we found that “Zhang Gu 13” (ZG, large panicle) exhibits a significantly higher panicle weight than “Yu Gu 18” (YG, conventional panicle) at the early stage of grain filling, but the weight of YG increased rapidly and gradually overtook ZG during the middle stages. A temporal expression pattern analysis demonstrated that the genes involved in photosynthesis, metabolic pathways, and phenylpropanoid biosynthesis were downregulated, while those related to peroxisome function, purine metabolism, and zeatin biosynthesis were upregulated during grain filling in both varieties. A total of 6,832 differentially expressed genes (DEGs) were identified in both varieties, with the majority identified at the early and late stages. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis further revealed that the upregulated DEGs in YG were associated with gibberellin (GA) biosynthesis, ATP-binding cassette (ABC) transporters, and plant hormone signal transduction. Photosynthesis-related DEGs, such as photosystem and antenna proteins, were significantly upregulated in ZG. This study provides preliminary insights into the differences in gene expression and molecular mechanisms of grain filling between ZG and YG in the North China summer-sowing region.

High temperature oxidation mechanisms of grain refined Fe-25Al-1.5Ta(+TaC/+(Ta,Nb)C) iron aluminides at 700 °C in air

The high temperature oxidation mechanisms of grain refined Fe-25Al-1.5Ta (at%) with TaC or (Ta,Nb)C additives were investigated at 700 °C in air for 503 h to study the influence of microstructural changes on the oxidation behaviour. While a thin and stable α-Al2O3 scale was formed at the Fe-Al matrix, additional phases were selectively oxidised leading to higher oxidation kinetics of Fe-25Al-1.5Ta with carbide additives. The selectively oxidised C14 (Fe,Al)2Ta Laves phase showed the formation of outer Fe2O3 and an inner (Al,Ta)-rich oxide, while Al-rich oxides were found along the (Al,Ta)-rich oxide/Fe-Al phase boundary and locally below Fe2O3.

Effect of ultrasonic field on microstructure evolution in friction stir welding of dissimilar Al/Mg alloys

Understanding of the microstructure evolution and the influence of ultrasonic vibration on friction stir welding (FSW) of dissimilar Al/Mg alloys is of great significance in optimizing the process parameters and improving the joint quality. In this study, the microstructure evolutions in the weld nugget zone (WNZ) of dissimilar Al/Mg joints during FSW and ultrasonic vibration enhanced FSW (UVeFSW) were characterized and compared. It was found that ultrasonic vibration (UV) has great effect on the grains structure of the WNZ in the Mg alloy side. Specially, the exerted UV changed the main dynamic recrystallization (DRX) mechanism of grains in the Mg alloy side from continuous DRX (CDRX) to discontinuous DRX (DDRX) under lower or higher welding speeds but constant tool rotation speed. Along the thickness direction, the average grain sizes near the bonding interface in the WNZ increased first and then decreased, and the maximum grain size was located at the mid-depth of the weld. Low strain shear texture appeared more in the WNZ of the Al alloy side during FSW, while in UVeFSW more locations in the WNZ were with high strain shear textures. The application of UV field improved the DRX degree in the whole weld through promoting the entanglement, aggregation and rearrangement of dislocations.

DNA Methylation and RNA-Sequencing Analysis Show Epigenetic Function During Grain Filling in Foxtail Millet (Setaria italica L.)

Grain filling is a crucial process for crop yield and quality. Certain studies already gained insight into the molecular mechanism of grain filling. However, it is unclear whether epigenetic modifications are associated with grain filling in foxtail millet. Global DNA methylation and transcriptome analysis were conducted in foxtail millet spikelets during different stages to interpret the epigenetic effects of the grain filling process. The study employed the whole-genome bisulfite deep sequencing and advanced bioinformatics to sequence and identify all DNA methylation during foxtail millet grain filling; the DNA methylation-mediated gene expression profiles and their involved gene network and biological pathway were systematically studied. One context of DNA methylation, namely, CHH methylation, was accounted for the largest percentage, and it was gradually increased during grain filling. Among all developmental stages, the methylation levels were lowest at T2, followed by T4, which mainly occurred in CHG. The distribution of differentially methylated regions (DMR) was varied in the different genetic regions for three contexts. In addition, gene expression was negatively associated with DNA methylation. Evaluation of the interconnection of the DNA methylome and transcriptome identified some stage-specific differentially expressed genes associated with the DMR at different stages compared with the T1 developmental stage, indicating the potential function of epigenetics on the expression regulation of genes related to the specific pathway at different stages of grain development. The results demonstrated that the dynamic change of DNA methylation plays a crucial function in gene regulation, revealing the potential function of epigenetics in grain development in foxtail millet.

Effect of abc Pressing at 573 K on the Microstructure and Martensite Transformation Temperatures in Ti49.8Ni50.2 (at%)

This paper presents experimental data on the microstructure and martensite transformation temperatures of Ti49.8Ni50.2 (at%) after abc pressing (multi-axial forging) to different true strains e from 1.84 to 9.55 at 573 K. The data show that increasing the true strain results in grain–subgrain refinement on different scales at a time. With e = 9.55 at 573 K, the average grain–subgrain size measured approximately 130 nm. Decreasing the abc pressing temperature from 723 to 573 K caused a decrease in all martensite transformation temperatures, a change in the lattice parameters, R phase formation, and angular shifts of diffraction peaks and their broadening. The largest change in the microstructure of Ti49.8Ni50.2 was provided by abc pressing to e = 1.84. Increasing the true strain to e = 9.55 resulted in a much smaller effect, suggesting that the alloy obtained a high density of structural defects even at e = 1.84. Two possible mechanisms of grain–subgrain refinement are discussed.

EFFECTS OF GRINDING WHEEL WEAR ON THE THERMO-MECHANICAL LOADS IN THE GRINDING PROCESS

A large amount of the energy produced during grinding is converted into heat. Since not all of the heat can be dissipated by the cooling lubricant, thermally induced displacements in machine components occur, which has a negative influence on the component quality. The generation and distribution of heat is influenced by the change of the grinding wheel topography due to wear.Therefore, the wear mechanisms of grains were identified and quantified and their effect on heat generation was investigated. For this purpose, creep feed grinding investigations on bearing steel were conducted with electroplated CBN grinding wheels with different grain specifications.

Correlation mechanism of grain orientation/microstructure and mechanical properties of Cu–Ni–Si–Co alloy

Abstract The relationship between the microstructure and properties of the different orientations of a Cu–Ni–Si–Co alloy was investigated by tensile testing, X-ray diffraction electron backscattering diffraction, transmission electron microscopy, and high-energy X-ray diffraction (HEXRD). The results revealed that the cold-rolled alloy contained mainly a Brass {110} and R {124} texture. The alloy was aged, and it exhibited mainly an R texture, and its volume and distributing width were 45.2% and 10.8°, respectively. The aged alloy exhibited obvious anisotropy, and its tensile strength and electrical conductivity in the rolling direction were 870 MPa and 50% IACS, respectively. In the Cu–Ni–Si–Co alloy, the orientation grains close to the [111] crystal plane were in the hard orientation zone, the Schmid factor value was low, and the material strength was relatively high. At the same time, the [111] crystal plane was close-packed and exhibited good conductivity. The oriented grains close to the [100] crystal plane was in the soft oriented zone and had lower strength and conductivity. Through HEXRD analysis, it was found that the oriented grains with a high twin stacking-fault probability had lower stacking fault energy, and the probability of aging-induced twinning was high.

Grain growth kinetics and grain refinement mechanism in Al2O3/WC/TiC/graphene ceramic composite

The grain growth kinetics and grain refinement mechanism of Al2O3 grains and WC grains in Al2O3/WC/TiC/graphene ceramic composite were investigated in this work. The grain growth exponent of Al2O3 was determined as 2, which conformed to the growth mechanism of grain boundary diffusion. Meanwhile, the grain growth exponent of WC was determined as 3, which conformed to the grain growth mechanism of volume diffusion or liquid-phase diffusion. The different wettability of graphene to Al2O3 and WC was responsible for their different grain growth mechanisms. By analyzing grain growth activation energy, it can be concluded that the grain growth of Al2O3 and WC went through three stages: (1) softening stage, (2) rapid growth stage and (3) stable stage. The grain refinement mechanism of Al2O3 grains was graphene pinning effect and intragranular structure, and the grain refinement of WC grains could be attributed to the strong bonding interface between WC and graphene.