Effects of Aging Treatment on the Microstructures and Mechanical Properties of a TC18 Alloy.

In the present work, the effects of aging treatment on the microstructures of a TC18 alloy are studied. The influence of aging treatment on the tensile properties and failure mechanisms is systematically analyzed. It is found that the size and morphology of the primary α (αp) phases are insensitive to aging temperature and time. Furthermore, the aging temperature and time dramatically influence the precipitation of the secondary α (αs) phases. Massive αs phases precipitate and gradually coarsen, and finally weave together by increasing the aging temperature or extending the aging time. The variations in αp and αs phases induced by aging parameters also affect the mechanical properties. Both yield strength (YS) and ultimate tensile strength (UTS) first increase and then decrease by increasing the aging temperature and time, while ductility first decreases and then increases. There is an excellent balance between the strengths and ductility. When the aging temperature is changed from 450 to 550 °C, YS varies from 1238.6 to 1381.6 MPa, UTS varies from 1363.2 to 1516.8 MPa, and the moderate elongation ranges from 9.0% to 10.3%. These results reveal that the thickness of αs phases is responsible for material strengths, while the content of α phases can enhance material ductility. The ductile characteristics of the alloy with coarser αs phases are more obvious than those with thinner αs phases. Therefore, the aging treatment is helpful for the precipitation and homogeneous distribution of αs phases, which are essential for balancing the strengths and ductility of the studied Ti alloy.

Investigation on Mechanism of Microstructure Evolution during Multi-Process Hot Forming of GH4169 Superalloy Forging.

Typically, in the manufacturing of GH4169 superalloy forgings, the multi-process hot forming that consists of pre-deformation, heat treatment and final deformation is required. This study focuses on the microstructural evolution throughout hot working processes. Considering that δ phase can promote nucleation and limit the growth of grains, a process route was designed, including pre-deformation, aging treatment (AT) to precipitate sufficient δ phases, high temperature holding (HTH) to uniformly heat the forging, and final deformation. The results show that the uneven strain distribution after pre-deformation has a significant impact on the subsequent refinement of the grain microstructure due to the complex coupling relationship between the evolution of the δ phase and recrystallization behavior. After the final deformation, the fine-grain microstructure with short rod-like δ phases as boundaries is easy to form in the region with a large strain of the pre-forging. However, necklace-like mixed grain microstructure is formed in the region with a small strain of the pre-forging. In addition, when the microstructure before final deformation consists of mixed grains, dynamic recrystallization (DRX) nucleation behavior preferentially depends on kernel average misorientation (KAM) values. A large KAM can promote the formation of DRX nuclei. When the KAM values are close, a smaller average grain size of mixed-grain microstructure is more conductive to promote the DRX nucleation. Finally, the interaction mechanisms between δ phase and DRX nucleation are revealed.

High-Temperature Compression Behaviors and Constitutive Models of a 7046-Aluminum Alloy.

High-temperature forming behaviors of a 7046-aluminum alloy were investigated by hot compression experiments. The microstructural evolution features with the changes in deformation parameters were dissected. Results indicated the formation of massive dislocation clusters/cells and subgrains through the intense DRV mechanism at low compression temperature. With an increase in deformation temperature, the annihilation of dislocations and the coarsening of subgrains/DRX grains became prominent, due to the collaborative effects of the DRV and DRX mechanisms. However, the growth of subgrains and DRX grains displayed the weakening trend at high strain rates. Moreover, two constitutive models involving a physically based (PB) model and a gate recurrent unit (GRU) model were proposed for predicting the hot compression features. By validation analysis, the predicted values of true stress perfectly fit with the experimental data, indicating that both the proposed PB model and the GRU model can accurately predict the hot compression behaviors of 7046-aluminum alloys.

Hot Deformation Behavior of Hastelloy C276 Alloy: Microstructural Variation and Constitutive Models.

Isothermal deformation experiments of the Hastelloy C276 alloy were executed using the Gleeble-3500 hot simulator at a temperature range of 1000-1150 °C and a strain rate range of 0.01-10 s-1. Microstructural evolution mechanisms were analyzed via transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). Results reveal that the influences of hot compression parameters on the microstructure variation features and flow behaviors of the Hastelloy C276 alloy were significant. The intense strain hardening (SH) effects caused by the accumulation of substructures were promoted when the strain rates were increased, and true stresses exhibited a notable increasing tendency. However, the apparent DRV effects caused by the annihilation of substructures and the increasingly dynamic recrystallization (DRX) behaviors occurred at high compressed temperature, inducing the reduction in true stresses. In addition, a physical-based (PB) constitutive model and a long short-term memory (LSTM) model optimized using the particle swarm optimization (PSO) algorithm were established to predict the flow behavior of Hastelloy C276 alloy. The smaller average absolute relative error and greater relation coefficient suggest that the LSTM model possesses a higher forecasting accuracy than the PB model.

Dislocation Substructures Evolution and an Informer Constitutive Model for a Ti-55511 Alloy in Two-Stages High-Temperature Forming with Variant Strain Rates in ß Region.

The high-temperature compression characteristics of a Ti-55511 alloy are explored through adopting two-stage high-temperature compressed experiments with step-like strain rates. The evolving features of dislocation substructures over hot, compressed parameters are revealed by transmission electron microscopy (TEM). The experiment results suggest that the dislocations annihilation through the rearrangement/interaction of dislocations is aggravated with the increase in forming temperature. Notwithstanding, the generation/interlacing of dislocations exhibit an enhanced trend with the increase in strain in the first stage of forming, or in strain rates at first/second stages of a high-temperature compressed process. According to the testing data, an Informer deep learning model is proposed for reconstructing the stress-strain behavior of the researched Ti-55511 alloy. The input series of the established Informer deep learning model are compression parameters (compressed temperature, strain, as well as strain rate), and the output series are true stresses. The optimal input batch size and sequence length are 64 and 2, respectively. Eventually, the predicted results of the proposed Informer deep learning model are more accordant with the tested true stresses compared to those of the previously established physical mechanism model, demonstrating that the Informer deep learning model enjoys an outstanding forecasted capability for precisely reconstructing the high-temperature compressed features of the Ti-55511 alloy.

Soil heavy metal pollution from Pb/Zn smelting regions in China and the remediation potential of biomineralization.

Smelting activities pose serious environmental problems due to the local and regional heavy metal pollution in soils they cause. It is therefore important to understand the pollution situation and its source in the contaminated soils. In this paper, data on heavy metal pollution in soils resulting from Pb/Zn smelting (published in the last 10 years) in China was summarized. The heavy metal pollution was analyzed from a macroscopic point of view. The results indicated that Pb, Zn, As and Cd were common contaminants that were present in soils with extremely high concentrations. Because of the extreme carcinogenicity, genotoxicity and neurotoxicity that heavy metals pose, remediation of the soils contaminated by smelting is urgently required. The primary anthropogenic activities contributing to soil pollution in smelting areas and the progressive development of accurate source identification were performed. Due to the advantages of biominerals, the potential of biomineralization for heavy metal contaminated soils was introduced. Furthermore, the prospects of geochemical fraction analysis, combined source identification methods as well as several optimization methods for biomineralization are presented, to provide a reference for pollution investigation and remediation in smelting contaminated soils in the future.

Effect of Deformation Parameters of an Initial Aged GH4169 Superalloy on Its Microstructural Evolution during a New Two-Stage Annealing.

This study aims to explore the effect of deformation parameters on microstructure evolution during the new two-stage annealing method composed of an aging treatment (AT) and a cooling recrystallization annealing treatment (CRT). Firstly, the hot compressive tests with diverse deformation parameters were finished for an initial aged deformed GH4169 superalloy. Then, the same two-stage annealing method was designed and carried out for the deformed samples. The results show that the deformation parameters mainly affect the grain microstructure during CRT by influencing the content, distribution and morphology of the δ phase after deformation. The reason for this is that there is an equilibrium of the content of the δ phase and Nb atom. When the deformation temperature is high, the complete dissolution behavior of the δ phase nuclei promotes the dispersion distribution of the δ phase with rodlike and needle-like shapes during AT. Thus, the fine and heterogeneous microstructure is obtained after annealing because the recrystallization nucleation is enhanced in those dispersed δ phases during CRT. However, when the retained content of δ phase nuclei is high after deformation, the clusters of intragranular δ phases will form during AT, resulting in the pinning of the motion for dislocation. The elimination of the mixed grain microstructure is slowed down due to the low static recrystallization (SRX) nucleation rate within the deformed grain.

Modeling Dynamic Recrystallization Behavior in a Novel HIPed P/M Superalloy during High-Temperature Deformation.

The dynamic recrystallization (DRX) features and the evolution of the microstructure of a new hot isostatic pressed (HIPed) powder metallurgy (P/M) superalloy are investigated by hot-compression tests. The sensitivity of grain dimension and DRX behavior to deformation parameters is analyzed. The results reveal that the DRX features and grain-growth behavior are significantly affected by deformation conditions. The DRX process is promoted with a raised temperature/true strain or a reduced strain rate. However, the grains grow up rapidly at relatively high temperatures. At strain rates of o.1 s-1 and 1 s-1, a uniform microstructure and small grains are obtained. Due to the obvious differences in the DRX rate at various temperatures, the piecewise DRX kinetics equations are proposed to predict the DRX behavior. At the same time, a mathematical model for predicting the grain dimension and the grain growth behavior is established. To further analyze the DRX behavior and the changes in grain dimension, the hot deformation process is simulated. The developed grain-growth equation as well as the piecewise DRX kinetics equations are integrated into DEFORM software. The simulated DRX features are consistent with the test results, indicating that the proposed DRX kinetics equations and the established grain-growth model can be well used for describing the microstructure evolution. So, they are very useful for the practical hot forming of P/M superalloy parts.

Intercomparison of global terrestrial carbon fluxes estimated by MODIS and Earth system models.

Earth system models (ESMs) have been widely used to simulate global terrestrial carbon fluxes, including gross primary production (GPP) and net primary production (NPP). Assessment of such GPP and NPP products can be valuable for understanding the efficacy of certain ESMs in simulating the global carbon cycle and future climate impacts. In this work, we studied the model performance of 22 ESMs participating in the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) by comparing historical GPP and NPP simulations with satellite data from MODIS and further evaluating potential model improvement from CMIP5 to CMIP6. In CMIP6, the average global total GPP and NPP estimated by the 22 ESMs are 16% and 13% higher than MODIS data, respectively. The multi-model ensembles (MME) of the 22 ESMs can fairly reproduce the spatial distribution, zonal distribution and seasonal variations of both GPP and NPP from MODIS. They perform much better in simulating GPP and NPP for grasslands, wetlands, croplands and other biomes than forests. However, there are noticeable differences among individual ESM simulations in terms of overall fluxes, temporal and spatial flux distributions, and fluxes by biome and region. The MME consistently outperforms all individual models in nearly every respect. Even though several ESMs have been improved in CMIP6 relative to CMIP5, there is still much work to be done to improve individual ESM and overall CMIP performance. Future work needs to focus on more comprehensive model mechanisms and parametrizations, higher resolution and more reasonable coupling of land surface schemes and atmospheric/oceanic schemes.

Microstructural Variation and a Physical Mechanism Model for a Ti-55511 Alloy during Double-Stage Hot Deformation with Stepped Strain Rates in the ß Region.

The microstructural variation and high-temperature flow features of a Ti-55511 alloy in the ß region are studied by utilizing double-stage compression with a stepped strain rate. The results demonstrate that the stresses in the latter stage of hot compression markedly reduce as the strain at the previous stage or the strain rate at the previous/latter stage drops. Moreover, the annihilation/interaction of substructures is promoted, and the distinct refinement of the dynamic recrystallization (DRX) in the ß grain can be found. However, the coarsening of the ß grain and the consumption of dislocation substructures are accelerated at high temperatures. Furthermore, the principal DRX nucleation mechanism of the Ti-55511 alloy during double-stage compression with a stepped strain rate in the ß region is discontinuous DRX. Additionally, by using the microstructural variation characteristics related to the forming parameters, a physical mechanism equation is modeled to forecast the forming features, the DRX fraction, and the size of the ß grain in the investigated alloy. The forecasted results are in accordance with the tested results, indicating that the established model can accurately forecast the microstructure variation and flow features of the studied alloy.

Microstructure Evolution and a Unified Constitutive Model of Ti-55511 Alloy Compressed at Stepped Strain Rates.

The flow behavior and microstructure change of the Ti-55511 alloy are investigated by thermal compression experiments with stepped strain rates. The phase transformation features, the dynamic recrystallization (DRX) behavior of the ß matrix, the dynamic spheroidization mechanism of the lamellar α phase and the evolution of the ß sub-grain size are quantitatively analyzed. A unified constitutive model is constructed to characterize the hot deformation features of the Ti-55511 alloy. In the established model, the work hardening effect is taken into account by involving the coupled effects of the equiaxed and lamellar α phases, as well as ß substructures. The dynamic softening mechanisms including the dynamic recovery (DRV), DRX and dynamic spheroidization mechanisms are also considered. The material parameters are optimized by the multi-objective algorithm in the MATLAB toolbox. The consistency between the predicted and experimental data indicates that the developed unified model can accurately describe the flow features and microstructure evolution of the hot compressed Ti-55511 at stepped strain rates.

Effects of Aging Treatment on Corrosion Behavior of a Tensile Deformed Al-Cu-Mn-Fe-Zr Alloy in 3.5% NaCl Solution.

In this paper, the effects of an aging treatment on the corrosion resistance/mechanism of a tensile deformed Al-Cu-Mn-Fe-Zr alloy are investigated. The impedance magnitude and polarization resistance increase, while the corrosion current decreases with the increased aging time and temperature. The discontinuously-distributed precipitates and precipitation-free zone, which can cut the corrosion channels, appear at grain boundaries when the temperature is relatively high and the aging time is relatively long. They can improve the corrosion resistance. Additionally, the intergranular and pitting corrosion are the main mechanisms. The intergranular corrosion is likely to occur in an under-aged alloy. This is because the potential difference between the grain boundaries and grains is high, due to the segregation of Cu atoms. When the aging degree is increased, the grain boundary precipitates reduce the potential difference, and the intragranular precipitates make the surrounding matrix prone to dissolution. As such, the pitting corrosion is likely to occur in the over-aged alloys.

Effects of Double-Stage Annealing Parameters on Tensile Mechanical Properties of Initial Aging Deformed GH4169 Superalloy.

This study takes large size samples after hot-upsetting as research objects and aims to investigate the optimization double-stage annealing parameters for improving the mechanical properties of hot-upsetting samples. The double-stage annealing treatments and uniaxial tensile tests for hot-upsetting GH4169 superalloy were finished firstly. Then, the fracture mode was also studied. The results show that the strength of hot-upsetting GH4169 superalloy can be improved by the double-stage annealing treatment, but the effect of annealing parameters on the elongation of GH4169 alloy at high temperature and room temperature is not significant. The fracture mode of annealed samples at high-temperature and room-temperature tensile tests is a mixture of shear fracture and quasi-cleavage fracture while that of hot-upsetting sample is a shear fracture. The macroscopic expressions for the two fracture modes belong to ductile fracture. Moreover, it is also found that the improvement of strength by the double-stage annealing treatment is greater than the single-stage annealing treatment. This is because the homogeneity of grains plays an important role in the improvement of strength for GH4169 superalloy when the average grain size is similar. Based on a comprehensive consideration, the optimal annealing route is determined as 900 °C × 9-12 h(water cooling) + 980 °C × 60 min(water cooling).

Evolution of Annealing Twins in a Hot Deformed Nickel-Based Superalloy.

The hot deformation characteristics of a GH4169 superalloy are investigated at the temperature and strain rate ranges of 1193-1313 K and 0.01-1 s-1, respectively, through Gleeble-3500 simulator. The hot deformed microstructures are analyzed by optical microscopy (OM), transmission electron microscopy (TEM), and electron backscattered diffraction (EBSD) technology. The effects of deformation parameters on the features of flow curves and annealing twins are discussed in detail. It is found that the shapes of flow curves are greatly affected by the deformation temperature. Broad peaks appear at low deformation temperatures or high strain rates. In addition, the evolution of annealing twins is significantly sensitive to the deformation degree, temperature, and strain rate. The fraction of annealing twins first decreases and then rises with the added deformation degree. This is because the initial annealing twin characters disappear at the relatively small strains, while the annealing twins rapidly generate with the growth of dynamic recrystallized grains during the subsequent hot deformation. The fraction of annealing twins is relatively high when the deformation temperature is high or the strain rate is low. In addition, the important role of annealing twins on dynamic recrystallization (DRX) behaviors are elucidated. The obvious bulging at initial twin boundaries, and the coherency of annealing twin boundaries with dynamic recrystallized grain boundaries, indicates that annealing twins can motivate the DRX nucleation during the hot deformation.

Strengthening of a Near ß-Ti Alloy through ß Grain Refinement and Stress-Induced α Precipitation.

Near ß-Ti alloys with high strength and good ductility are desirable for application in aviation and aerospace industries. Nevertheless, strength and ductility are usually mutually exclusive in structural materials. Here we report a new thermo-mechanical process, that is, the alloy was cross-rolled in ß field then aged at 600 °C for 1 h. By such a process, a high strength (ultimate tensile strength: 1480 MPa) and acceptable ductility (elongation: 10%) can be simultaneously achieved in the near ß-Ti alloy, based on the microscale ß matrix and nanoscale α phase. The microstructure evolution, mechanical properties and strengthening mechanisms have been clarified by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the grain size of the ß phase progressively decreased with the increasing of rolling reduction. Moreover, dense dislocation structures and martensite phases distributed in the cross-rolled ß matrix can effectively promote the precipitation of nanoscale α particles. TEM analyses confirmed that a heat-treatment twin was generated in the newly formed α lath during aging. These findings provide insights towards developing Ti alloys with optimized mechanical properties.

Study on the Polar Extracts of Dendrobium nobile, D. officinale, D. loddigesii, and Flickingeria fimbriata: Metabolite Identification, Content Evaluation, and Bioactivity Assay.

The polar extract of the Dendrobium species or F. fimbriata (a substitute of Dendrobium), between the fat-soluble extract and polysaccharide has barely been researched. This report worked on the qualitative and quantitative studies of polar extracts from D. nobile, D. officinale, D. loddigesii, and F. fimbriata. Eight water-soluble metabolites containing a new diglucoside, flifimdioside A (1), and a rare imidazolium-type alkaloid, anosmine (4), were identified using chromatography as well as spectroscopic techniques. Their contents in the four herbs were high, approximately 0.9⁻3.7 mg/g based on the analysis of quantitative nuclear magnetic resonance (qNMR) spectroscopy. Biological activity evaluation showed that the polar extract of F. fimbriata or its pure component had good antioxidant and neuroprotective activity; compounds 1‒4 and shihunine (8) showed weak α-glucosidase inhibitory activity; 4 and 8 had weak anti-inflammatory activity. Under trial conditions, all samples had no cytotoxic activity.

Xyloketal B exerts antihypertensive effect in renovascular hypertensive rats via the NO-sGC-cGMP pathway and calcium signaling.

Xyloketal B (Xyl-B) is a novel marine compound isolated from mangrove fungus Xylaria sp. (No 2508). We previously showed that Xyl-B promoted endothelial NO release and protected against atherosclerosis through the Akt/eNOS pathway. Vascular NO production regulates vasoconstriction in central and peripheral arteries and plays an important role in blood pressure control. In this study, we examined whether Xyl-B exerted an antihypertensive effect in a hypertensive rat model, and further explored the possible mechanisms underlying its antihypertensive action. Administration of Xyl-B (20 mg·kg-1·d-1, ip, for 12 weeks) significantly decreased the systolic and diastolic blood pressure in a two-kidney, two-clip (2K2C) renovascular hypertensive rats. In endothelium-intact and endothelium-denuded thoracic aortic rings, pretreatment with Xyl-B (20 µmol/L) significantly suppressed phenylephrine (Phe)-induced contractions, suggesting that its vasorelaxant effect was attributed to both endothelial-dependent and endothelial-independent mechanisms. We used SNP, methylene blue (MB, guanylate cyclase inhibitor) and indomethacin (IMC, cyclooxygenase inhibitor) to examine which endothelial pathway was involved, and found that MB, but not IMC, reversed the inhibitory effects of Xyl-B on Phe-induced vasocontraction. Moreover, Xyl-B increased the endothelial NO bioactivity and smooth muscle cGMP level, revealing that the NO-sGC-cGMP pathway, rather than PGI2, mediated the anti-hypertensive effect of Xyl-B. We further showed that Xyl-B significantly attenuated KCl-induced Ca2+ entry in smooth muscle cells in vitro, which was supposed to be mediated by voltage-dependent Ca2+ channels (VDCCs), and reduced ryanodine-induced aortic contractions, which may be associated with store-operated Ca2+ entry (SOCE). Taken together, these findings demonstrate that Xyl-B exerts significant antihypertensive effects not only through the endothelial NO-sGC-cGMP pathway but also through smooth muscle calcium signaling, including VDCCs and SOCE.

α-Glucosidase inhibitory and cytotoxic botryorhodines from mangrove endophytic fungus Trichoderma sp. 307.

One new depsidone, botryorhodine H (1), together with three known analogues, botryorhodines C, D and G (2-4), were obtained from the mangrove endophytic fungus Trichoderma sp. 307 by co-culturing with Acinetobacter johnsonii B2. Structures were determined by 1D and 2D NMR analyses and high-resolution mass spectrum. Compounds 1-3 showed α-glucosidase inhibitory activity with IC50 ranging from 8.1 to 11.2 µM, and compound 1 exhibited potent cytotoxicity against rat prolactinoma MMQ and rat pituitary adenoma GH3 cell lines (IC50 = 3.09 and 3.64 µM).

Phochrodines A-D, first naturally occurring new chromenopyridines from mangrove entophytic fungus Phomopsis sp. 33.

Four new chromenopyridine derivatives, phochrodines A-D (1-4), were identified from mangrove entophytic fungus Phomopsis sp. 33# by means of various modern chromatographic, spectroscopic and single crystal X-ray diffraction techniques. Compounds 1-4 with an unusual 5H-chromeno[4,3-b]pyridine skeleton were the first naturally occurring chromenopyridines. Their anti-inflammatory, antioxidant and cytotoxic activities were evaluated. 3 and 4 showed moderate inhibition of nitric oxide production with IC50 values of 49.0 as well as 51.0µM, respectively. 4 had well ability to scavenge DPPH radical with IC50 value of 34.0µM. The four had no cytotoxic activity for MDA-MB-435 breast cancer cells.

Induction of Diverse Bioactive Secondary Metabolites from the Mangrove Endophytic Fungus Trichoderma sp. (Strain 307) by Co-Cultivation with Acinetobacter johnsonii (Strain B2).

Two new sesquiterpenes, microsphaeropsisin B (1) and C (2), and two new de-O-methyllasiodiplodins, (3R, 7R)-7-hydroxy-de-O-methyllasiodiplodin (4) and (3R)-5-oxo-de-O-methyllasiodiplodin (5), together with one new natural product (6) and twelve known compounds (3, 7-17), were isolated from the co-cultivation of mangrove endophytic fungus Trichoderma sp. 307 and aquatic pathogenic bacterium Acinetobacter johnsonii B2. Their structures, including absolute configurations, were elucidated by extensive analysis of spectroscopic data, electronic circular dichroism, Mo2(AcO)4-induced circular dichroism, and comparison with reported data. All of the isolated compounds were tested for their α-glucosidase inhibitory activity and cytotoxicity. New compounds 4 and 5 exhibited potent α-glucosidase inhibitory activity with IC50 values of 25.8 and 54.6 µM, respectively, which were more potent than the positive control (acarbose, IC50 = 703.8 µM). The good results of the tested bioactivity allowed us to explore α-glucosidase inhibitors in lasiodiplodins.