Search Results (108)

In the framework of high temperature components, the need to evaluate the accumulated creep damage during service life is fundamental to extend the life of components which are currently deemed as scrap as per design intent. Thus, the life assessment of Ni-based superalloys could be performed in relation to the accumulated creep deformation which represents the limiting factor for serviced components. Despite the different microstructural changes that occur in service life, this work focuses on the possibility to evaluate the material strain by means of electron backscattered diffraction (EBSD). The key point is the identification of the correlation between geometrically necessary dislocation (GND) density derived from EBSD analyses and the reached creep strain for a single crystal Ni-based superalloy. However, the results of GND density are affected by the settings’ parameters adopted to perform the analysis by the magnification level and the step size. These two parameters have been optimized by analyzing specimens from interrupted creep tests at strain levels between 0.5% and 10%, in the temperature range between 850 °C and 1000 °C. Full article

In this study, a multi-gradient microstructure was introduced into medium-Mn steel through torsion following heat treatment at different annealing temperatures, and through investigations on the mechanical properties under two annealing temperatures, it has also been revealed that different annealing temperatures before torsion affect the stability of austenite after torsion, thereby leading to distinct variations in mechanical performance. The yield strengths of the studied steel after annealing at 600 °C and 620 °C were 762 MPa and 673 MPa, with total elongation of 47.4% and 44.1%, respectively. After 90° torsion, the yield strength of experimental steels increased to 834 MPa and 808 MPa, while the elongation decreased to 21.6% and 29.5%, respectively. The gradient distributions from the center to the edge were observed for the austenite volume fraction, average grain size, martensite volume fraction, GND density, and hardness. The comparative analysis of the two annealing temperatures indicates that the larger grain size in the 620—annealed sample leads to its lower yield strength, while its higher austenite volume fraction and moderate stability promote a more sustained TRIP effect during deformation, contributing to its enhanced elongation. This multi-gradient microstructure is responsible for the yield strength improvements of 72 MPa and 135 MPa in the torsioned samples annealed at 600 °C and 620 °C, respectively. Full article

The laser welding of 4 mm thick Ti80 alloy under different powers was analyzed, and the weld morphology, microstructure, and mechanical properties were studied. A simulation model was established based on ABAQUS, and laser welding simulations were conducted using 2520 W and 3000 W laser welding power sources to analyze the temperature field and stress field, which were verified by experiments. The increase in power changed the weld morphology from Y-shaped to X-shaped and affected the number of pores in incomplete and complete penetration. The microstructure in the weld zone presented fine acicular α′ phase. Subsequently, grain boundary distribution maps, Kernel Average Misorientation (KAM) maps, and geometrically necessary dislocation (GND) density maps were generated through electron backscatter diffraction (EBSD) analysis. These comprehensive data visualizations enabled multi-dimensional investigation, establishing and analyzing correlations between laser welding parameters, microstructural evolution, and mechanical properties in Ti80 titanium laser welding. The hardness of the base material was 320 HV to 360 HV, and it increased from 420 HV to 460 HV in the weld zone. At 3000 W, the tensile strength reached 903.12 MPa, and the elongation was 10.40%, indicating ductile fracture. The simulation results accurately predicted the maximum longitudinal residual stress in the weld zone, with an error of 1.65% to 1.81% of the measured value. Full article

Introduction: Both preeclampsia (PE) and prediabetes (PD) are known hypertensive disorders of pregnancy, and a correlation has been shown between these two diseases. A recent study in our laboratory has shown that pregestational PD is a risk factor for developing PE during pregnancy, as pregestational PD increased antiangiogenic factors. However, pregestational PD antiangiogenic release has not been shown to be associated with liver dysfunction. Therefore, this study seeks to investigate pregestational PD as a risk factor for hemolysis, elevated liver enzymes, and low platelet (HELLP) syndrome. Materials and Methods: Animals were divided into a normal pregnant group (ND), a preeclamptic pregnant group (PE), and a prediabetic pregnant group (PD). On gestational day (GND) 19, animals were sacrificed, and blood and liver tissues were collected to measure antioxidant protection and lipid peroxidation parameters, liver TGs, liver enzymes, TNF-α, IL-6, and hematology parameters. Results: The results showed significant increases in liver TGs, liver enzymes, TNF-α, IL-6, and hematology parameters in the PE and PD pregnant groups compared to the ND group. Conclusions: These findings suggest that pregestational PD predisposes patients to metabolic and inflammatory changes associated with HELLP syndrome. To our knowledge, this is the first study to demonstrate a link between pregestational PD and HELLP syndrome-related complications in a preclinical model, highlighting the importance of monitoring metabolic health before pregnancy. Full article

This paper uses a combination of nanoindentation experiments and mechanism-based models to determine the dislocation densities and plasticity length scales associated with the nanoindentation of barite rock materials. These include estimates of the plasticity length scale, geometrically necessary dislocation densities (GNDs) and statistically stored dislocation densities (SSDs) that are shown to have major implications for the plastic deformation of geomaterials such as barite rocks. The statistical variations associated with the nanoindentation of barite rocks are also measured along with local variations in surface composition that are also elucidated via energy dispersive X-ray spectroscopy (EDS) during Scanning Electron Microscopy (SEM). The indentation size effects are shown to be greater than the statistical variations due to local differences in surface composition. The effects of local variations in surface composition are also discussed before relating the measured hardness values to the underlying dislocation densities (GNDs and SSDs) and plasticity length scale parameters using strain gradient plasticity theories. The presence of hard minerals such as quartz and other silicate minerals, as confirmed by the elemental composition of the rock samples, contributed significantly to the average hardness, elastic modulus, plasticity and relatively high dislocation densities. The implications of the results are discussed for the energy-efficient drilling and blasting of rocks, constitutive modeling of barite rock deformation and the crushing of rocks during mineral processing. Full article

The maintenance of intracellular redox homeostasis depends on the GSH/GSSG pair, which is the primary intracellular redox buffer. However, the NADPH/NADP⁺ pair also plays a vital role in this process. The primary source of NADPH is the pentose phosphate pathway and deficiency in the enzymes responsible for NADPH production in this pathway leads to developing of alternative NADPH supply strategies. The choice of compensation strategy has several consequences for cells physiology. The present study investigates how Saccharomyces cerevisiae yeast strains defective in generating NADPH via the pentose phosphate pathway due to deletion of ZWF1, GND1, or GND2 genes, respond to redox homeostasis disruption caused by allyl alcohol, a metabolic precursor of acrolein. Acrolein is a highly reactive aldehyde that rapidly depletes glutathione and triggers oxidative stress. Therefore, cells respond to acrolein through attempts to increase glutathione synthesis, but also by increasing NADPH production. The response requires coordinated action of glutathione- and NADPH-dependent systems. The high sensitivity of the Δgnd1 strain, which is unable to activate an adequate stress response, is evidence of this. The strategy employed by this strain to maintain redox homeostasis is inadequate and may even exacerbate allyl alcohol toxicity. Full article

The development of low-cost and high-performance Mg alloys is an important way to achieve further application of magnesium alloys. In this work, the as-extruded Mg_98.3−xZn_xGd₁Sm_0.7 alloy with excellent mechanical properties is successfully prepared by regulating the bimodal-grained structure. The effect of the Zn content on the microstructure evolution and mechanical properties of the as-extruded Mg_98.3−xZn_xGd₁Sm_0.7 alloy is systematically investigated. The results show that the addition of Zn increases the dynamic recrystallization (DRX) fraction and weakens the basal texture of the as-extruded alloy. The Mg_98.05Zn_0.25Gd₁Sm_0.7 alloy exhibits a typical bimodal-grained structure. A large amount of geometrically necessary dislocations (GNDs) are generated at the interface between the soft zone and the hard zone of the bimodal-grained structure during the plastic deformation process, resulting in back stress strengthening, thereby improving the strength of the alloy. And it achieves exceptional mechanical properties with an ultimate tensile strength (UTS) of 330 MPa, a yield strength (YS) of 248 MPa, and an elongation (EL) of 18.5% at room temperature. This paper provides a new idea for introducing a heterogeneous structure and improving the strength of low-cost Mg alloys. Full article

It has become a trend to precisely control the additive manufacturing process parameters within the high-density process window to obtain high-performance metal parts. However, there are few reports on this topic currently, leaving this research without sufficient references. This study took 316L austenitic stainless steel as a case study. In total, 36 groups of specimens were manufactured by Laser powder bed melting (LPBF), and then, two highly dense specimens were selected to study the variation in their microstructure and properties. The densities of the selected specimens, S1 (VED = 81 J/mm³) and S2 (VED = 156.3 J/mm³), are 99.68% and 99.99%, respectively. The results indicated that, compared with the S1 specimen, the S2 specimen significantly decreased in terms of yield strength (YS), ultimate tensile strength (UTS), and elongation (EL), which are 7.28%, 6.34%, and 19.15%, respectively. The differences in mechanical properties were primarily attributed to differences in their microstructures. Further, compared with the S1 specimen, the fitted ellipse aspect ratio and average grain size of the S2 specimen increased by 79.88% and 53.45%, respectively, and the kernel average misorientation (KAM) value and geometric necessary dislocation (GND) density increased by 36.00% and 58.43%, respectively. Furthermore, the S1 specimen exhibited a strong texture in the <101>//Z direction, whereas no obvious texture was observed in the S2 specimen. Obviously, the reason why precise regulation within the dense parameter range can achieve better performance is that the microstructure and mechanical properties of the specimens prepared within the dense range are different. More importantly, this study provides a feasible framework for optimizing alloys with broad and dense parameter ranges, demonstrating the potential to achieve high-performance components through precise parameter control. Furthermore, the results reveal that even within a wide range of high-density forming parameters, significant variations in microstructure and mechanical properties can arise depending on the selected parameter combinations. These findings underscore the critical importance of meticulous process parameter optimization and microstructural regulation in tailoring material properties. Full article

Nowadays, members of the genus Enterobacter have been documented as human and aquaculture pathogens. To date, no reports have described Enterobacter bugandensis infecting Hippocampus abdominalis. In the present study, an isolate of E. bugandensis, designated H4, was identified as a causative pathogen in cultured H. abdominalis following Koch’s postulate, and its virulence properties were further described. The isolate’s genome consisted of a single circular chromosome and harbored several virulence and resistance genes, including, but not limited to, csgG, acrB, hcp, gndA, galF, rpoS, fur, rcsB, and phoP involved in adherence, antimicrobial activity, effector delivery systems, immune modulation, and regulation, as well as baeR, blaACT-49, ramA, hns, ftsI, acrA, gyrA, fabI, crp, oqxB, parE, gyrB, phoP, rpoB, tuf, ptsI, and fosA2 functioning against aminoglycoside, cephamycin, disinfecting agent and antiseptic, fluoroquinolone, macrolide, peptide, and other antimicrobials. Additionally, the isolate exhibited multiple resistance to cephalosporins, penicillins, and tetracyclines and demonstrated a median lethal dose (LD₅₀) of 4.47 × 10⁵ CFU/mL in H. abdominalis. To our knowledge, this is the first study to describe E. bugandensis infecting H. abdominalis. These findings highlight the zoonotic potential of E. bugandensis and underscore the need for targeted health management in seahorse farming. Full article

A Mg-Gd-Y alloy prepared by surface mechanical attrition treatment (SMAT) was annealed at 450 °C combined with peak aging. The deformation and fracture mechanisms were investigated using in situ tensile tests. Through quantitative calculations of the geometrically necessary dislocation (GND) densities, it was found that the fine-grained (FG) layer in the gradient structure carried greater plastic strain than the coarse-grained (CG) layer during tension. The calculation results of the geometric compatibility parameter (m’) and microstructure characterization during in situ tests showed that crack initiation and propagation were prone to occur between adjacent coarse grains. However, the hetero-deformation-induced (HDI) strengthening and strain hardening induced by the strain gradient between the FG and CG layers effectively improved the strength–ductility synergy of the gradient-structured (GS) alloy. In addition, the synergistic effect of intrinsic and extrinsic toughening mechanisms in the GS alloy played a significant role in delaying premature failure. Full article

Fracture toughness anisotropy is a key concern in IN718 components produced by Laser Powder Bed Fusion (LPBF), due to their strong crystallographic texture and characteristic lamellar microstructure. In this study, the effect of grain orientation on fracture toughness was evaluated by testing two LPBF IN718 builds with the same laser scanning strategy (R0), but with two different orientations: vertical (R0-0) and 45° inclined (R0-45) relative to the build direction. The mechanical response was assessed through compact tension (CT) tests following ASTM E399 and ASTM E1820 standards. Results show that the R0-45 specimens exhibited a fracture toughness nearly 2.5 times higher than R0-0 specimens. Detailed microstructural analysis, supported by EBSD and SEM, reveals that the higher toughness in the R0-45 orientation is linked to a combination of smaller effective grain size along the crack path, higher levels of geometrically necessary dislocations (GND), and increased kernel average misorientation (KAM), which collectively enhance plastic accommodation and crack-tip shielding. These findings support and reinforce the established understanding of the relationship between microstructure and anisotropic fracture behavior in LPBF IN718, facilitating its practical application in the design and orientation of additively manufactured components. Full article

The inhibition of recrystallization in high-strain nickel-based single-crystal superalloys remains a critical challenge for advanced turbine blade applications. This study investigates the evolution of the primary γ’ phase and dislocation during annealing in a third-generation Re-containing single-crystal superalloy (WZ30) subjected to 5% compressive deformation. Isochronal annealing (700 to 1200 °C, 1 min) combined with scanning electron microscopy (SEM) and an electron backscatter diffraction (EBSD) analysis revealed a nonlinear variation of the geometrically necessary dislocation (GND) density, which reached a minimum of 1000 °C with 62.7% of the primary γ’ phase retained. Prolonged recovery annealing at 1000 °C for 10 h effectively inhibited recrystallization during subsequent solution heat treatment. This result provides a practical strategy for inhibiting recrystallization in single-crystal superalloys. Full article

In the Direct Energy Deposition (DED) process, the deposited material experiences intricate thermo-mechanical processes. Subsequent thermal cycling can trigger Dynamic Recrystallization (DRX) under suitable conditions, with specific strain and temperature parameters facilitating grain refinement and homogenization. While prior research has examined the impact of thermal cycling in continuous wave (CW) lasers on DRX in 316 L stainless steel deposits, this study delves into the effects of pulsed wave (PW) laser thermal cycling on DRX. Here, the thermo-mechanical response to PW cyclic thermal loading is empirically assessed, and the evolution of microstructure, grain morphology, geometric dislocation density (GND), and misorientation map during PW DED of 316 L stainless steel is scrutinized. Findings reveal that DRX is activated between the 8th and 44th thermal cycles, with temperatures fluctuating in the range of 680 K–750 K–640 K and grains evolving within a 5.6%–6.2%–5.2% strain range. After 90 thermal cycles, the grain microstructure undergoes significant alteration. Throughout the thermal cycling, dynamic recovery (DRV) occurs, marked by sub-grain formation and low-angle grain boundaries (LAGBs). Continuous dynamic recrystallization (CDRX) accompanies discontinuous dynamic recrystallization (DDRX), with LAGBs progressively converting into high-angle grain boundaries (HAGBs). Elevated temperatures and accumulated strain drive dislocation movement and entanglement, augmenting GND. The study also probes the influence of frequency and duty cycle on grain microstructure, finding that low pulse frequency spurs CDRX, high pulse frequency favors DRV, and the duty cycle has minimal impact on grain microstructure under PW cyclic thermal load. Full article

Sintered silver, widely used in WBG electronic device packaging for its excellent electrothermal properties and high-temperature stability, faces challenges in macroscopic mechanical behavior and reliability due to porosity, especially for pressureless sintered silver. However, the intrinsic pores inside sintered material introduce uncertainties during nanoindentation tests for mechanical characterization. This study investigated the impact of pore distribution on the dislocation behavior of pressureless sintered silver during nanoindentation. Firstly, pressureless sintered silver models with 8–33% porosity were prepared and characterized through scanning electron microscope (SEM) for porosity, electron backscatter diffraction (EBSD) for the geometrically necessary dislocation (GND) density distribution, and transmission electron microscopy (TEM) for the crystal structure and microscopic strain. The EBSD results indicated that nanoindentation caused localized plastic deformation in sintered silver, closely related to its porous structure. The TEM results revealed that sintered silver undergoes dislocation slip during nanoindentation, leading to complex dislocation network formation, while the strain decreased with distance from the indentation. To further investigate the relationship of pore distribution and dislocation behavior during nanoindentation, molecular dynamics (MD) simulations were carried out. The MD results revealed that the dislocation distribution was consistent with the EBSD and TEM results. During loading, with the increased porosity from 10% to 23.7%, the total dislocation length was reduced by 63%, while it led to a 38% increase in total dislocation length with the average pore size decreased from 3.84 nm to 2.88 nm under similar porosity conditions. This study improves the understanding of the deformation mechanisms of porous sintered silver under nanoindentation and provides insight into the mechanical characterization of porous materials. Full article

Riboflavin (vitamin B₂) is an essential micronutrient required for all living organisms. It is naturally synthesized by plants and most microorganisms, including the bacterium Bacillus subtilis, the filamentous fungus Ashbya gossypii, and the yeast Candida famata—all of which are known to be riboflavin overproducers. The choice of production organism in industrial applications depends on factors such as yield, ease of cultivation, and the availability of genetic tools. As a result, several microorganisms are commonly used, and their relative prominence can shift over time with advances in metabolic engineering and process optimization. This review presents a comparative analysis of riboflavin biosynthesis across prokaryotic and eukaryotic systems, with a particular focus on regulatory mechanisms governing flavinogenesis. Special attention is given to recent advances in metabolic engineering strategies, including the application of CRISPR/Cas9 genome editing in Bacillus subtilis and Ashbya gossypii. In yeast systems, significant improvements in riboflavin production have been achieved primarily through the manipulation of transcriptional regulators (e.g., SEF1, SFU1, TUP1) and metabolic genes. The role of other important genes (PRS3, ADE4, ZWF1, GND1, RFE1, VMA1, etc.) in riboflavin overproduction in C. famata is described. The review also explores the use of alternative, low-cost feedstocks—including lignocellulosic hydrolysates and dairy by-products—to support more sustainable and economically viable riboflavin production. Although considerable progress has been achieved in genetic optimization and bioprocess development, further work is required to fine-tune metabolic flux and maximize riboflavin synthesis, particularly under industrial conditions. This review highlights key opportunities for future research aimed at refining metabolic interventions and expanding the use of renewable substrates for environmentally sustainable riboflavin production. Full article