Crystalline Microstructure Research Articles

Thermal and Structural Analysis of a High-Entropy Cr16Mn16Fe16Co16Ni16P20 Alloy—Influence of Cooling Rates on Phase Transformations

This study investigates the influence of cooling rates on the microstructure and phase transformations of the high-entropy alloy Cr16Mn16Fe16Co16Ni16P20. The alloy was synthesized via arc melting and subjected to three cooling conditions: slow cooling (52 K/s), accelerated cooling after a short electric arc pulse (3018 K/s), and rapid quenching (10⁵–10⁶ K/s) using the melt-spinning method. The microstructures were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Mössbauer spectroscopy. The thermal properties and phase transformations were analyzed using differential scanning calorimetry (DSC) and thermography. Slow cooling produced a complex crystalline microstructure, while accelerated cooling resulted in fewer phases. Rapid cooling yielded an amorphous structure, demonstrating that phosphorus and high mixing entropy enhance glass-forming ability. Phase transformations exhibited significant undercooling under accelerated cooling, with FCC phase crystallization shifting from 1706 K (slow cooling) to 1341 K, and eutectic crystallization from 1206 K to 960 K. These findings provide a foundation for optimizing cooling processes in high-entropy alloys for advanced structural and functional applications.

Effects of Reduction‐Oxidation Cycles on the Structure, Heat and Corrosion Resistance of Haynes 282 Nickel Alloy Manufactured by Using Powder Bed Fusion‐Laser Beam Method

ABSTRACTThe study investigated the effect of the oxidation–reduction cycles on the structure and corrosion resistance of the Haynes 282 nickel superalloy at ambient and elevated temperatures. The comparative studies were performed on specimens produced by the Powder Bed Fusion‐Laser Beam (PBF‐LB) process and those in the as‐received state. The microstructure of the PBF‐LB specimens was studied using optical and scanning electron microscopy, whereas the chemical composition of the scale formed after isothermal oxidation in an air atmosphere at 750°C was analysed using energy‐dispersive X‐ray spectroscopy and X‐ray Photoelectron Spectroscopy. The phase composition of the formed scale was determined by X‐ray diffraction. Laboratory‐induced hydrogen atmosphere was adopted through cathodic charging. A comparison of corrosion resistance was carried out on two types of Haynes 282 specimens, before and after the oxidation and cathodic charging processes. It was found that PBF‐LB process could be effectively used to manufacture Haynes 282 nickel superalloy with low porosity and a fine crystalline microstructure. The low‐porous, fine‐crystalline microstructure of the tested specimens produced by the PBF‐LB technique exhibited good resistance to electrochemical corrosion, slightly lower than wrought Haynes 282 nickel superalloy specimens.

Study on the Effect of Coal Grain Size on the Morphology of Soot Generated During Combustion

This study performed an experimental exploration to analyze the influence of different grain sizes of coal on the nanostructure and morphological parameters of soot generated during combustion. Initially, primary and mature soot samples were gained from the combustion flames of two different grain sizes of coal (less than 150 μm, named sample #1, and 6–8 mm, named sample #2) by using thermophoresis sampling technology. Subsequently, the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate and analyze the soot samples, with the aim of obtaining their morphological parameters and nanostructure characteristics. The TEM images indicate that the nascent soot produced during the flame formed by small-sized coal is relatively uniform, with individual particles 8–14 nm in size. The grain size of the nascent soot produced by large-sized coal is much larger, within a wide range of 50–350 nm. Additionally, the nanostructures of the nascent soot particles produced by samples #1 and #2 mainly consist of upright parallel crystal stripes. The crystal stripes of the soot particles formed by sample #1 have obvious microcrystalline structures, whereas only a small amount of microcrystalline structure is found at the edge of sample #2. Compared with sample #2, the soot formed during the combustion of sample #1 exhibits a denser crystalline structure. The SEM results indicate that the mature soot agglomerates formed in sample #2 are larger and more in quantity compared to sample #1. Furthermore, the mature soot agglomerates formed in sample #2 have a stronger coagulation performance and a more compact structure than that formed in sample #1.

Synergy of Nanocrystallinity, Temperature, and "the Third Element Effect" for Uncommon Oxidation Resistance of Fe-Cr-Al Alloys.

Nanocrystalline structure, oxidation temperature, and "The Third Element Effect" are among the factors that can profoundly govern the characteristics of the oxide scales that develop on oxidation-resistant alloys, thereby, their synergistic effect can considerably influence alloys' oxidation kinetics. As a result of the synergy, certain iron-chromium-aluminium (Fe-Cr-Al) alloy showed superior oxidation resistance at 800°C than at 700°C (whereas oxidation resistance commonly decreases with the increase in temperature). The superior resistance at higher temperatures is considerably enhanced when the structure of the alloy is nanocrystalline vis-à-vis the common microcrystalline structure. Nanocrystalline alloy oxidizes at a negligible rate (c.f., its microcrystalline counterpart). The characterization of the oxide scale demonstrates that the oxidation temperature governs the formation of the protective oxide scale with/without the assistance of the "Third element Effect". The findings may potentially have considerable commercial implications.

Microcrystalline-Fe2P4O12 as eco-friendly and efficient anode for high-performance dual-ion battery

Dual-ion batteries (DIBs) have garnered significant interest because of their cost-effectiveness and high level of safety. However, the anode typically utilized tends to show low cyclic stability in complete batteries when the only sources of lithium are primarily consumed in the electrolyte following the development of a solid electrolyte interphase (SEI) during the initial electrochemical process. Here, a simple approach is used to produce microcrystalline carbon-coated Fe2P4O12 at a mild temperature. This material has the ability to store lithium ions, resulting in a specific capacity of 215 mAh/g at a potential range of 1 to 2.5 V vs Li+/Li0. Furthermore, it demonstrates a remarkable coulombic efficiency of 99 % in the initial cycles, even in the absence of a solid electrolyte interphase (SEI) formation. On the other hand, the issue of the high voltage plateau of the graphite cathode is addressed by selecting a total of 4.2 V as the optimal voltage range in DIBs. Simultaneously, the composite Fe2P4O12 also demonstrates exceptional ion diffusion kinetics and reduced interfacial impedance due to its microcrystalline structure. The utilization of the proposed Fe2P4O12 anode addresses a crucial deficiency in the complete range of deep in-situ bioremediation techniques, hence expediting the industrialization process.

3D-printed laponite bioceramic triply periodic minimal surface scaffolds with excellent bioactivity for bone regeneration

Laponite (LAP) is a promising biomaterial for bone regeneration due to its reliable biocompatibility and excellent osteoinductivity in bone tissue engineering. However, the personalized manufacture of LAP bioceramic scaffolds with controlled complex architecture and high porosity remains challenging. This study used vat photopolymerization (VPP) to manufacture LAP bioceramic scaffolds with high precision and biological activity. We first selected a 40 wt% LAP bioceramic slurry for subsequent VPP printing based on stability experiments and viscosity characterization results. The curing parameters of the photosensitive bioceramic slurry and the degassing sintering process were studied to ensure the quality of the ceramic green bodies. Then, we characterized the effects of different sintering temperatures (1150 °C, 1200 °C, 1250 °C) on the crystalline phase composition, microstructure, and mechanical properties of the LAP bioceramic. The research showed that the densification and compressive strength of the LAP bioceramic sintered at 1250 °C reached 2.51 g/cm3 and 15 Mpa, respectively. Finally, the bioceramic scaffolds with different sintering temperatures were co-cultured with rat bone marrow mesenchymal stem cells to detect biocompatibility. The results showed that the three groups of scaffolds enhanced cell proliferation, adhesion, and osteogenic capacity. In conclusion, the LAP bone scaffolds by VPP presented the potential for bone repair.

Relationship of CO2 adsorption performance and physicochemical property of biochar prepared by different types of biomass waste

The physicochemical property of biochar prepared by biomass waste is crucial for CO2 adsorption performance. However, the quantified relationship between the physicochemical property and CO2 adsorption capacity for biochar is still unclear. In this study, biochar samples with different physicochemical properties were prepared from six representative biomass of sewage sludge, chicken manure, apple and prickly ash branch, corn and rice straw. The quantitative investigation was conducted and the relationship between the physicochemical properties and CO2 adsorption capacity of biochar was analysed using Pearson correlation analysis method. The results showed that the biochar prepared from prickly ash branch at 800 °C pyrolysis exhibited a better CO2 adsorption capacity of 154.44 mg/g and larger specific surface area of 160.83 m2/g, compared with other biochars. According to the quantitative data about physicochemical properties of twenty-four kinds of biochar samples, the correlations between CO2 adsorption capacity and microcrystalline structure, surface functional groups, nitrogen content and specific surface area were obtained. The CO2 adsorption capacity showed a significant positive correlation with the specific surface area (SBET), stacking height of aromatic layers (Lc), number of aromatic layers (N) and nitrogen content, and the correlation order was SBET >N >Lc = nitrogen content. Moreover, the CO2 adsorption capacity showed a negative correlation with diameter of aromatic planes (La), CO, O-H and index of aromaticity (Aal/Aar), and the order of correlation was CO > O-H >La >Aal/Aar. The effect mechanism of physicochemical properties on CO2 adsorption of biochar was that microcrystalline structure had an influence on CO2 adsorption by van der Waals force, and nitrogen, oxygen-containing functional groups, and so on by Lewis acid-base interaction and hydrogen bonding.

Substrate and Step Rate Dependence Electrodeposition of Nickel–Cobalt–Molybdenum–Phosphorous Alloy for Efficient Hydrogen Evolution Reaction

Understanding the hydrogen economy involves recognizing the crucial role of water‐splitting in producing green, clean, and carbon‐free hydrogen. In that respect, the role of catalyst is very important as it enhances the reaction rate and efficiency, making hydrogen production more viable and sustainable. Herein, nickel–cobalt–molybdenum–phosphorous (Ni–Co–Mo–P) alloy has shown efficient catalysis properties for hydrogen evolution reaction (HER) in an alkaline medium. The quaternary alloys are directly grown on different substrates like nickel sheet, copper sheet, and stainless‐steel sheet by employing a simple pulse electrodeposition method. The method is conducted with a pulse interval time of 15 s at various pulse rates while maintaining the pH of 4 at room temperature. The alloy deposition is performed at a potential range from −1.5 V to −0.15 V (vs Ag/AgCl). The electrodeposition of the alloy in different substrates is first established with X‐Ray diffraction (XRD), field‐emission scanning electron microscopy (FESEM), and Raman spectroscopy. The deposited quaternary alloy exhibits the lowest overpotential of −163 mV at 10 mA cm−2 for copper substrate with a Tafel slope of 154 mV dec−1. The microcrystalline structure or amorphous nature and the rough grain surface of Ni‐Co‐Mo‐P alloys have characterized by XRD and scanning electron microscopy micrograph, respectively.

Periodically Sinusoidal Magnetic Stray Field and Improved Film Quality of CoMnP Micro-Magnet Arrays for Magnetic Encoders by Electrodeposition with the Assistance of Ultrasound

Magnetic encoders are composed of a magnetic sensor, a hard magnetic recording medium and a signal processing circuit. Electrodeposited micro-magnet arrays produced by micro-fabrication are promising recording media for enhancing encoder performance. However, two major engineering issues have yet to be resolved. One issue is an unknown relationship between the feature sizes of micro-magnet arrays and their stray field shapes, and another issue is the formation of micro-cracks due to the built-up residual stresses of thick films. In this study, we investigated the effect of feature sizes on the emanating stray field shape at various observation heights. Feature sizes include two height (i.e., film thickness) values of 78 μm and 176 μm, and both width and spacing with three values of 360 μm, 520 μm and 680 μm. Ultrasound-assisted agitation was adopted for investigating the effects of electrodepositing current densities on the film crystalline microstructures and magnetic properties. Narrowing the width of micro-magnets helps the stray field to become a sinusoidal profile. Thinner film, i.e., thickness 78 μm in this study, supports the stray field taking on a sinusoidal profile. Moreover, the spacing between the micro-magnets plays a key factor in determining the shape of the stray field. Under 37 kHz/156 W ultrasound agitation, the optimal hard magnetic properties of electrodeposited CoMnP films are residual magnetization 2329 G and coercivity 968 Oe by a current density of 10.0 mA/cm2. Ultrasound-assisted electrodeposition, along with duly designed feature size, facilitates the micro-magnet arrays having a sinusoidal stray field shape using high quality films. Furthermore, for the first time, a systematic understanding of feature-size-dependent stray field evolution and improved polarities quality has been realized for the recording media of sinusoidal magnetic encoders.

Sulfuric acid treatment to control the microcrystalline structure of starch-based hard carbon for sodium storage

By treating starch with different concentrations of sulfuric acid, we investigated the effect of cross-linked starch-based hard carbon on the performance of sodium-ion batteries (SIBs) at various concentrations. After treatment, the optimal sample exhibits a spherical microstructure, which can provide effective active sites and enhance structural stability, thereby achieving high capacity and long cycle life for SIB electrodes. In subsequent electrochemical tests, after 100 cycles at low current density of 0.1 A g−1, the capacity of H40 remains of 306 mA h g−1. And under the high current density of 1 A g−1, the capacity of H40 can still maintain of 228 mA h g−1, exhibiting a high capacity retention rate of 89 %, which is higher than other samples. This study provides a promising approach for the large-scale production of biomass-derived carbonaceous SIBs anodes.

Improved thermal, mechanical, and dielectric properties of thermotropic liquid crystalline poly(ester amide)s containing lactam-derived segmental units

We prepared two different series of thermotropic liquid crystalline poly(ester amide)s (TPEAs) via bulk polycondensation reactions of 4-hydroxybenzoic acid (HBA, 75.0 mol %) and 6-hydroxy-2-naphthoic acid (HNA, 25.0–17.5 mol %) with ε-caprolactam (CL, 0.0–7.5 mol %) or γ-butyrolactam (BL, 0.0–7.5 mol %). Our investigation aimed to explore the impact of lactam-derived aliphatic amide units’ length and content on the liquid crystalline feature, microstructure, thermal transition, thermal stability, mechanical/relaxational/rheological behavior, and dielectric characteristics of TPEAs. The molecular structure and fibrillar formation of TPEAs containing aliphatic amide units were confirmed through FT-IR and SEM analysis. With increasing CL or BL-derived units from 1.0 mol % to 5.0 mol %, we observed an increase in crystallinity, glass transition temperature, melting temperature, complex melt viscosity, and storage modulus of TPEAs, attributed to the enhanced intermolecular hydrogen bonding interactions. However, at 7.5 mol % CL or BL-derived unit content, these properties decreased due to increased chain irregularity as well as lowered crystallinity. Notably, the dielectric constants (3.31–3.04 at 2 MHz) of TPEAs decreased with the increase of lactam-derived aliphatic amide units owing to the restricted chain mobility by intermolecular hydrogen bonding interactions. We believe that the TPEAs synthesized in this study hold significant potential for applications in technical plastics, superfibers, and printed circuit board materials.

Potential skincare benefits and self-healing properties of Lignosus rhinocerotis polysaccharides as affected by ultrasound-assisted H2O2/Vc treatment

Natural polysaccharides have been recognized as major bioactive components in skincare and wound care products. In this study, the skincare benefits and self-healing properties of Lignosus rhinocerotis polysaccharides (LRP) and its degraded products (DLRP-1, DLRP-2 and DLRP-3) by ultrasound assisted H2O2/Vc treatment (U-H/V) at different ultrasonic intensity (28.14, 70.35, and 112.56 W/cm2) were investigated. U-H/V altered the internal crystalline structure and microstructure of LRP, and enhanced the thermal stability. Due to the breakage of molecular chains after U-H/V, the moisture absorption of LRP was enhanced but the moisturizing property showed a different degree of reduction. U-H/V significantly improved the antioxidant, anti-tyrosinase and anti-inflammatory activities of LRP. Furthermore, the results of enzyme kinetic studies showed a mixed competitive-noncompetitive inhibition of tyrosinase activity by DLRP-3 and the inhibition constant of DLRP-3 on tyrosinase was 2.97 mg/mL. The apparent viscosity of LRP dispersions showed a first increasing followed by decreasing trend as ultrasonic intensity rose. U-H/V enhanced the viscoelastic properties of LRP gels without destroying their self-healing properties. This findings reveal that U-H/V is beneficial for improving the skincare efficacy of LRP, providing a theoretical foundation for the applicability of LRP in wound dressings.

Nitrogen‐Induced Microcrystalline‐to‐Nanocrystalline Structure Transition in Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition: Comparison of N2 and NH3 Precursors

The structure and properties of polycrystalline chemical vapor deposition (CVD) diamond coatings grown by microwave plasma CVD in H2–CH4 mixtures can be effectively controlled by nitrogen admixture in the process gas. Here, a comparative study of adding nitrogen from different precursors, N2 and ammonia NH3, in concentrations up to 0.4%vol on grain size, texture, surface roughness, and sp2/sp3 ratio of the produced films on Si substrates is performed. A transition from microcrystalline to smooth nanocrystalline diamond structure is found to occur at a certain concentration of the precursor, for NH3 this threshold concentration being much lower, 0.02–0.1%, than for N2. The higher activity of ammonia is associated with easier formation of cyano radicals in the plasma as detected with optical emission spectroscopy, in accord with the lower bond‐dissociation energy for NH3 compared to N2. On the contrary, a smaller addition (0.004%) of either N2 or NH3 promotes almost doubling of the growth rate, while preserving the microcrystalline structure of the film. The results establish ammonia as a convenient alternative precursor to commonly used N2 added in the plasma for the diamond film structure modifications.

Microcrystalline and nanocrystalline structure of diamond films grown by MPCVD with nitrogen additions: Study of transitional synthesis conditions

This research explores the complex influence of nitrogen concentration and substrate temperature on the resultant properties of polycrystalline diamond (PCD) films grown by microwave plasma chemical vapor deposition (CVD). In particular, we investigated the growth parameters to find the exact conditions for changing the morphology of the resulting film from microcrystalline (MCD) to nanocrystalline (NCD). A series of 2 µm-thick polycrystalline diamond films was grown on Si substrates in methane-hydrogen–nitrogen gas mixtures with varied: (i) nitrogen concentration (0–2 %) and (ii) substrate temperature (700–1050 °C). Comprehensive characterization techniques, including scanning electron microscopy (SEM), micro-Raman spectroscopy, and X-ray diffraction, were employed to assess the morphological, structural, and spectroscopic properties of the films. The study reveals that even minor additions of nitrogen significantly modulate secondary nucleation, impacting both film morphology and phase composition. Furthermore, substrate temperature emerges as another critical parameter, influencing the growth kinetics and crystallite size. The comparison of the characteristics of grown PCD films allowed us to find conditions for the formation of NCD films with minimal surface roughness and maximal growth rate: nitrogen concentration [N2] ≈ 0.2–0.5 % and temperature T ≈ 850–900 °C. These findings can be used to optimize the CVD synthesis parameters of PCD films for applications as protective or friction-reducing layers, as well as for superhard cutting tools and optical devices.

Cellulose nanocrystal (CNC) from okra plant (Abelmoschus esculentus L.) stalks as a reinforcement in bionanocomposite fabrication: Extraction, processing, and characterization study

Currently, CNC is attractive to the researchers to fabricate multifunctional bionanocomposite because of their outstanding physicochemical, thermomechanical, morphological properties, and eco-friendly nature. Whereas in most cases CNC is extracted from the bast/bark of primary plants, which have other beneficial applications in several sectors. Hence, it is crucial to find out alternative sources of CNCs to diminish the extra pressure on the primary plants. While the useless agrowaste biomass of okra stalks would be a new and beneficial alternative to produce CNCs as a reinforcement. Here, a series of chemical reactions were directed to produce CNCs. The samples were characterized by FTIR-ATR,TGA/DTA,FESEM,EDX,XRD,UV–vis-NIR, and DLS analysis. The obtained results suggested that the newly produced CNCs possessed substantial active functional groups(–OH,CO-C,–NH), high thermal stability, greater crystallinity(86.09±0.001 %), and notable microstructure indicating a well-organized porous surface with encouraging spherical shapes. The CNCs are free from impurities and coloring materials; additionally, they exhibit a highly negative surface charge and smaller particle sizes. It can be stated that the produced CNCs should have a good agreement with the sustainable environment and be beneficially applied as a reinforcing agent to fabricate bionanocomposites. Also acts as a sustainable alternative to the fossil-based hazardous ones for various uses.

Effect of equal channel angular pressing on microstructure and mechanical properties of a Cu-Cr-Ni-Si-Co alloy

The microstructural and properties of a Cu-Cr-Ni-Co-Si alloy produced by equal channel angular pressing (ECAP) were systematically investigated. After the fourth-pass ECAP deformation, the average grain size was refined from 30 μm (solid solution state) to below 3 μm, resulting in a fine and regularly shaped equiaxed crystalline microstructure. The distribution of grain boundaries became more uniform. During ECAP deformation, the volume fraction of Copper texture {001} <100> decreased, while that of the Brass {011} <211> increased, and the Shear {123} <634> remained nearly constant. An increase in the number of ECAP deformation passes facilitated dynamic recrystallization, leading to an increase in the fraction of the recrystallized texture. After thermomechanical treatment (first-pass ECAP +450 °C aged/120 min + 80 % cold-deformation +450 °C aged/30 min), the alloy exhibited good mechanical properties, with a tensile strength of 546 MPa, a yield strength of 475 MPa, an elongation of 18.2 %, and an electrical conductivity of 52.8 %IACS. The main strengthening mechanisms included precipitation strengthening, dislocation strengthening and grain boundary strengthening, with the precipitation strengthening accounting for 45.6 % of the yield strength.

Ablative property and mechanism of pitch-based carbon fiber modified C/C composites with high thermal conductivity

The novel C/C composites with thermal transport function were prepared using the mesophase-pitch carbon fibers (CFMP) as the thermal diffusion channels. The introduction of CFMP greatly improved the microstructure, thermal properties, and ablative resistance of the C/C composites. During the graphitization process, compared with PAN fibers (CFPAN), CFMP was more likely to be graphitized to form a highly ordered three-dimensional graphite structure. The highly organized microcrystalline structure of CFMP resulted in a tight interface with PyC that lessened the likelihood of flaws and cracks during graphitization. CFMP, which acted as a thermal conduction skeleton, significantly improved the thermal conductivity of C/C composites. After 3000 °C HTT, the thermal conductivity of C/C-3000-Z composites was increased to 51.70 and 225.02 W/(m K) in the XY and Z planes, respectively. During the ablation process, C/C-3000-Z specimen exhibited a lower temperature gradient and less thermal stress owing to the outstanding thermal properties and fewer defects. After 30 s ablation, the temperature difference of surface and backside was only 495.9 °C, and the mass and linear ablation rates were 0.3 μm/s and 0.9 mg/s, respectively.

Step-by-Step Tuning of Tribological and Anticorrosion Performance of Zinc Phosphate Conversion Coatings through Effective Integration of Spherical P-Doped MoS2 Nanoparticles.

Surface coatings with enhanced mechanical stability, improved tribological performance, and superior anticorrosion performance find immense application in various industrial sectors. Herein, we report the development of multifunctional composite zinc phosphate coatings by the effective integration of a structurally and morphologically tuned P-doped MoS2 nanoparticle additive (3P-MoS2) into the zinc phosphate matrix to offer attractive characteristics suitable for industrial applications. The integration of spherical nanoparticles as additive leads to the formation of homogeneous and compact coatings with a densely packed crystalline microstructure having enhanced microhardness, distinctive leaf-like morphology, and comparatively smooth topographical features. The attractive lubricity of the additive (3P-MoS2), coupled with its spherical morphology, facilitates a transition from sliding to rolling friction and contributes significantly toward the performance enhancement of the tuned composition of the composite zinc phosphate coating (0.3-PMS). Thus, the tuned 0.3-PMS coating delivers the lowest specific wear rate (1.334 × 10-5 mm3/Nm) and coefficient of friction (0.114) that significantly outperform bare-zinc phosphate coating. Further, the electrochemical corrosion study results indicate the improvement in corrosion resistance behavior of the composite zinc phosphate coatings with reduced corrosion current density (icorr) and charge transfer resistance (Rct) values, as compared to the bare-zinc phosphate coating. The effect of passivation in conjunction with the barrier protection characteristics of the composite coatings induced by the optimal composition of the integrated additive nanoparticles (3P-MoS2) can efficiently prevent the infiltration of corrosive ions and thereby significantly reduce the rate of corrosion.

Scale-span feature of surface analysis, macromolecular and pore structure in coal: Implications for inherent evolutionary mechanism of morphological microstructure

Morphological microstructural evolution of tectonic coal determines CBM storage and transportation mechanism as well as the occurrence of coal and gas outburst. Scale-span morphological feature of original and tectonic coals was characterized by AFM, Raman spectrum and physisorption method. The results demonstrate that metamorphism could remold the surface property of coal from rugged band to flat porous structure with pore form factor from 0.572 to 0.831, promoting the formation of regular and round pores. Tectonism facilitates ability of gas sorption in coal, breaking the basic structural integrity. Metamorphism could facilitate the ordered macromolecular structural evolution on recombination and aromatization as well as condensation; besides, tectonism may promote the evolution and development of microcrystalline structure in advance. The aforementioned results have revealed essential differences in morphological microstructure between original and tectonic coals, which are of great guiding significance to safe mining of CBM and prediction of coal and gas outburst.

Coupled cellular automata-crystal plasticity modeling of microstructure-sensitive damage and fracture behaviors in deformation of α-titanium sheets affected by grain size

Concerning the micro-scale deformation of titanium metal sheets, the number of grains in the sheet thickness direction decreases, and their formability exhibits a strong grain size sensitivity. Meanwhile, the twinning-induced dynamic recrystallization (TDRX) associated with grain size significantly affects the fracture behavior in the microforming of titanium sheets. Therefore, an accurate prediction of formability to improve manufacturing reliability remains challenging in the microforming of miniaturized titanium components. To address this issue, an in-depth understanding of the grain size-dependent TDRX behavior and its role in damage and fracture development in the microforming of α-titanium sheets is critical, and a coupled cellular automata-crystal plasticity (CA-CP) modeling framework was thus developed as an approach providing efficient solutions and insightful comprehensions of the issue. For the proposed modeling framework, a kinematic model for TDRX was established and integrated into the CP model by the CA algorithm. As a result, the microstructure evolution caused by TDRX was regarded as an intrinsic part of the constitutive behavior to connect heterogeneous plastic deformation and damage evolution through data transmission between the CP model and the CA algorithm. Additionally, the coupled CA-CP modeling framework was validated with the internal defect morphologies and deformation microstructures characterized by X-ray computed tomography (X-CT) and electron backscattered diffraction (EBSD). Experiment and simulation results demonstrated that the fine recrystallized (DRXed) grains were generated after the twin fragmentation when the dislocation density at twin boundaries reached a threshold of 9.2 × 1013 /m2. After TDRX, the dislocation density and the stress concentration intensity in recrystallization regions were revealed to decrease, accounting for the ductility improvement. Nevertheless, the dislocation density at twin boundaries was determined to decrease with the increase of grain size, leading to less twin fragmentation and the absence of TDRX. The uncoordinated deformation between fine DRXed grains motivated defects to grow spherically into microvoids, thereby preventing premature intergranular cracks along twins/grain boundaries. Ultimately, the deformation microstructures resulting from TDRX with the decrease of grain size were confirmed to control the brittle to ductile fracture transition of α-titanium sheets. The presented modeling framework and simulation procedure were validated to be able to predict the material integrity affected by crystalline microstructure in the deformation of titanium metal sheets.