Stress-Corrosion-Cracking Sensitivity of the Sub-Zones in X80 Steel Welded Joints at Different Potentials.

X80 steel plays a pivotal role in the development of oil and gas pipelines; however, its welded joints, particularly the heat-affected zone (HAZ), are susceptible to stress corrosion cracking (SCC) due to their complex microstructures. This study investigates the SCC initiation mechanisms of X80 steel welded joints under practical pipeline conditions with varying levels of cathodic protection. The SCC behaviors were analyzed through electrochemical measurements, hydrogen permeation tests, and interrupted slow strain rate tensile tests (SSRTs) conducted in a near-neutral pH environment under different potential conditions (OCP, -1.1 VSCE, -1.2 VSCE). These behaviors were influenced by microstructure type, grain size, martensite/austenite (M/A) constituents, and dislocation density. The sub-zones of the weld exhibited differing SCC resistance, with the fine-grain (FG) HAZ, base metal (zone), welded metal (WM) zone, and coarse-grain (CG) HAZ in descending order. In particular, the presence of coarse grains, low dislocation density, and extensive M/A islands collectively increased corrosion susceptibility and SCC sensitivity in the CGHAZ compared to other sub-zones. The SCC initiation mechanisms of the sub-zones within the X80-steel welded joint were primarily anodic dissolution (AD) under open-circuit potential (OCP) condition, shifting to either hydrogen-enhanced local plasticity (HELP) or hydrogen embrittlement (HE) mechanisms at -1.1 VSCE or -1.2 VSCE, respectively.

Improved Bending Strength and Thermal Conductivity of Diamond/Al Composites with Ti Coating Fabricated by Liquid-Solid Separation Method.

In response to the rapid development of high-performance electronic devices, diamond/Al composites with high thermal conductivity (TC) have been considered as the latest generation of thermal management materials. This study involved the fabrication of diamond/Al composites reinforced with Ti-coated diamond particles using a liquid-solid separation (LSS) method. The interfacial characteristics of composites both without and with Ti coatings were evaluated using SEM, XRD, and EMPA. The results show that the LSS technology can fabricate diamond/Al composites without Al4C3, hence guaranteeing excellent mechanical and thermophysical properties. The higher TC of the diamond/Al composite with a Ti coating was attributed to the favorable metallurgical bonding interface compounds. Due to the non-wettability between diamond and Al, the TC of uncoated diamond particle-reinforced composites was only 149 W/m·K. The TC of Ti-coated composites increased by 85.9% to 277 W/m·K. A simultaneous comparison and analysis were performed on the features of composites reinforced by Ti and Cr coatings. The results suggest that the application of the Ti coating increases the bending strength of the composite, while the Cr coating enhances the TC of the composite. We calculate the theoretical TC of the diamond/Al composite by using the differential effective medium (DEM) and Maxwell prediction model and analyze the effect of Ti coating on the TC of the composite.

Significant reduction in creep life of P91 steam pipe elbow caused by an aberrant microstructure after short-term service.

P91 steel is an important steam pipe for ultra-supercritical power plants due to its excellent creep strength, which generally has a design life of 100,000 h. Here, we found a significant aberrant decrease in the creep rupture life of a main steam pipe elbow after only 20,000 h of service. The microstructure in the aberrant piece exhibited a decomposition of martensitic lath into blocky ferrite due to recrystallization and accumulation of M23C6 as well as formation of the Laves phase along the prior austenitic grain boundaries, resulting in the decrease of hardness that no long meet ASME standard requirement. The creep testing of the P91 piece at 550-600 °C and 85-140 MPa shows that the influence of temperature on the cavity formation and cracking is greater than that of the applied stress. The rupture life is nearly two orders of magnitude shorter than the normal P91, attributing to the creep damage of the subgrain growth, M23C6 and Laves phase coarsening (aggregation approaching 3.4 µm). The residual life of the aberrant piece was evaluated to be 53,353 h based on the Larson-Miller parameter, which is much shorter than the design life, suggesting the safety operation of the elbow area should be paid more attention during the afterward service periods. P91 steel, main steam pipe elbow, aberrant microstructure, service degradation, creep life prediction.

Precipitation Evolution in the Austenitic Heat-Resistant Steel HR3C upon Creep at 700 °C and 750 °C.

HR3C (25Cr-20Ni-Nb-N) is a key material used in heat exchangers in supercritical power plants. Its creep properties and microstructural evolution has been extensively studied at or below 650 °C. The precipitation evolution in HR3C steel after creep rupture at elevated temperatures of 700 °C and 750 °C with a stress range of 70~180 MPa is characterized in this paper. The threshold strength at 700 °C and 750 °C were determined by extrapolation method to be σ105700= 57.1 MPa and σ105750=37.5 MPa, respectively. A corresponding microstructure investigation indicated that the main precipitates precipitated during creep exposure are Z-phase (NbCrN), M23C6, and σ phase. The dense Z-phase precipitated dispersively in the austenite matrix along dislocation lines, and remained stable (both size and fraction) during long-term creep exposure. M23C6 preferentially precipitated at grain boundaries, and coarsening was observed in all creep specimens with some continuous precipitation of granular M23C6 in the matrix. The brittle σ phase formed during a relatively long-term creep, whose size and fraction increased significantly at high temperature. Moreover, the σ phases, grown and connected to form a large "island" at triple junctions of grain boundaries, appear to serve as nucleation sites for high stress concentration and creep cavities, weakening the grain boundary strength and increasing the sensitivity to intergranular fracture.

Gradual increasing dyslipidemia in treatment-naive male patients with human immunodeficiency virus and treated with tenofovir plus lamivudine plus efavirenz for 3 years.

INTRODUCTION: Since the development of antiretroviral therapy (ART) with TDF plus 3TC plus EFV, this specific regimen has not been studied enough with long-term lipid and uric acid monitoring. METHODS: A prospective follow-up cohort study was performed. Sixty-one treatment-naive male patients with human immunodeficiency virus (HIV) were divided into three groups based on their baseline CD4+ cell count (26, 12, and 23 patients in the < 200, 200 to 350, and > 350 groups, respectively). The lipid and purine metabolism parameters of the patients over 144 weeks were analyzed. RESULT: Within 144 weeks, TG, LDL-c, TC and HDL-c gradually increased, especially TC and HDL-c (P = 0.001, 0.000, respectively). Moreover, the percentages of hyper-cholesterolemia, hyper LDL cholesterolemia, hyper-triglyceridemia and low HDL cholesterolemia also gradually increased, especially low HDL cholesterolemia significantly increased (P = 0.0007). The lower the baseline CD4+ cell counts were, the higher the TG levels and the lower the TC, LDL-c and HDL-c levels were. But there was significant difference of only baseline LDL-c levels between the three groups (P = 0.0457). No significant difference of the UA level and the percentages of hyperuricemia was found between the different follow-up time point groups or between the three CD4+ cell counts groups (all P > 0.05). The risk factors for dyslipidemia included age, anthropometric parameters and follow-up weeks, and for hyperuricemia was virus load. CONCLUSIONS: Gradual increasing dyslipidemia was found in male patients with human immunodeficiency virus primarily treated with tenofovir plus lamivudine plus efavirenz for 3 years. There-fore lipid metabolism parameters should be closely monitored during long-term ART with the TDF plus 3TC plus EFV regimen.

Lymphocyte subsets with the lowest decline at baseline and the slow lowest rise during recovery in COVID-19 critical illness patients with diabetes mellitus.

BACKGROUND: Host dysregulation of immune response was highly involved in the pathological process of Coronavirus disease 2019 (COVID-19), especially COVID-19 severe cases with DM. AIM: In this study we aimed at the dynamic change of peripheral lymphocyte and subsets during COVID-19 covery. METHODS: The peripheral lymphocyte and subsets of 95 confirmed cases with COVID-19 from baseline to four weeks were compared between critical illness and non-critical illness cases with or without DM. RESULTS: The dynamic characteristics of lymphocyte and subsets in COVID-19 patients was that it reduced significantly at one week, rapidly elevated to the peak at two weeks after onset, then gradually declined during recovery. The COVID-19 critical illness patients with DM had the lowest decline at one week and the slow lowest rise at two weeks after onset, while COVID-19 non-critical illness patients with DM had the rapid highest rise at two weeks after onset, both of them had similar lymphocyte and subsets at five weeks after onset and lower than those patients without DM. CONCLUSIONS: These findings provide a reference for clinicians that for COVID-19 patients with DM and the lowest decline of lymphocyte and subsets, immunomodulatory therapy as soon as possible might avoid or slow down disease progression; moreover for COVID-19 critical illness patients with or without DM and non-critical illness patients with DM, continuous immunomodulatory therapy in later stages of disease might speed up virus clearance, shorten hospital stay, improve disease prognosis in COVID-19 critical illness patients with DM.

Transcriptome analysis reveals novel insights into the continuous cropping induced response in Codonopsis tangshen, a medicinal herb.

Codonopsis tangshen Oliv. (C. tangshen Oliv.), a famous medicinal herb in China, is seriously affected by continuous cropping (C-cro). The physiological and biochemical results indicated that C-cro significantly affected the malonaldehyde (MDA) and chlorophyll content, as well as activities of catalase (CAT) and superoxide dismutase (SOD) when compared with the non-continuous cropping (NC-cro) group. Transcriptome profiling found 762 differentially expressed genes, including 430 up-regulated and 332 down-regulated genes by C-cro. In addition, pathway enrichment analysis revealed that genes related to 'Tyrosine degradation I', 'Glycogen synthesis' and 'Phenylalanine and tyrosine catabolism' were up-regulated, and genes associated with 'Signal transduction', 'Immune system', etc. were down-regulated by C-cro. The expression of target genes was further validated by Q-PCR. In this study, we demonstrated the effects of C-cro on C. tangshen at the transcriptome level, and found possible C-cro responsive candidate genes. These findings could be further beneficial for improving the continuous cropping tolerance.

Effect of Shot Peening on Oxidation Behavior of SS304H Upon Long Term Steam Exposure.

Specimens of austenitic stainless steel 304H (SS304H) were shot peened and exposed to steam at 600, 650, and 700 °C for 10,000 h, 15,000, and 20,000 h. After steam exposure, un-peened SS304H has three oxide layers, Fe-O, Fe-Cr-O and Cr2O3, while shot peened specimens have an Fe-Cr-O layer, a Cr2O3 and an amorphous Fe-Si-O layer. The evolution of the oxide layers as a function of duration of steam exposure and temperature reveals that the growth of the Fe-O and the Fe-Cr-O layers is inhibited by shot peening. The oxide layers in shot peened specimens are much thinner, indicating that shot peening enhances the oxidation resistance of SS304H. Grain refinement during shot peening enhances the diffusion of Cr and Si to help form a protective, oxidation resistant surface.

Microstructural Evolution of Super304H Upon Ultrasonic Shot Peening and Subsequent Annealing.

In this study we analyze the effect of shot peening on the microstructure and mechanical properties of Super304H, which is widely used for boiler tubes. Specimens were shot peened for 5, 10, and 15 minutes, and then heat treated at 600, 700, and 800 °C for 15 minutes. Vickers hardness was measured and the microstructure of cross sectional specimens was analyzed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). Heat treatment led to particle refinement on the upper layer of Super304H. In this region, nanograins, twins, and dislocations were generated to a depth of ~400 µm. The microstructure of the shot peened specimen did not change even after a heat treatment at 700 °C. However, rapid grain growth was observed after rapid annealing at 800 °C. Precipitation hardening occurred after heat treatment at 800 °C.

[Absorption and Distribution of Nitrogen,Phosphorus and Potassium in Atractylodes macrocephala].

Objective: To investigate the absorption and distribution of nitrogen（ N ), phosphorus（ P） and potassium（ K） in Atractylodes macrocephala by field experiment. Methods: The samples of Atractylodes macrocephala were carried out in different growing periods,and the amount of dry matter and the contents of N,P and K in different parts of the plant were determined,respectively. Results: The results showed that one-year-old Atractylodes macrocephala of budding stage and rhizome swelling stage were the key period of rapid nutrient absorption, and the absorbed nutrient element mainly allocated to the aerial part. For the two-year-old Atractylodes macrocephala, flowering stage was the key period of rapid nutrient absorption, and the absorbed nutrient element mainly allocated to the rhizome. The average N,P2O5 and K2O absorption per 100 kg rhizome product in two-year-old Atractylodes macrocephala were 2. 65,0. 91 and 2. 16 kg, respectively. Conclusion: In addition to the appropriate base fertilizer, one-year-old Atractylodes macrocephala cultivation should pay attention to the topdressing during the budding stage and the rhizome swelling stage, while the two-year-old Atractylodes macrocephala cultivation should pay attention to the topdressing during the flowering stage.

Transmission electron microscopy study of microstructural properties and dislocation characterization in the GaN film grown on the cone-shaped patterned Al2O3 substrate.

Growing a GaN film on a patterned Al2O3 substrate is one of the methods of reducing threading dislocations (TDs), which can significantly deteriorate the performance of GaN-based LEDs. In this study, the microstructural details of the GaN film grown on a cone-shaped patterned Al2O3 substrate were investigated using high-resolution transmission electron microscopy and weak-beam dark-field techniques. Various defects such as misfit dislocations (MDs), recrystallized GaN (R-GaN) islands and nano-voids were observed on the patterned Al2O3 surfaces, i.e. the flat surface (FS), the inclined surface (IS) and the top surface (TS), respectively. Especially, the crystallographic orientation of R-GaN between the GaN film and the inclined Al2O3 substrate was identified as $[\overline 1 2\overline 1 0]_{{\rm GaN}} \hbox{//}[\overline 1 101]_{{\rm R - GaN} \,{\rm on}\,{\rm IS}} \hbox{//}[\overline 1 100]_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $, $(\overline 1 012)_{{\rm GaN}} \hbox{//}(1\overline 1 02)_{{\rm R - Ga}\,{\rm Non}\,{\rm IS}} \hbox{//}(\overline {11} 26)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $. In addition, a rotation by 9° between $(10\overline 1 1)_{{\rm R - GaN}} $ and $(0002)_{{\rm GaN}} $ and between $(10\overline 1 1)_{{\rm R - GaN}} $ and $(0006)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $ was found to reduce the lattice mismatch between the GaN film and the Al2O3 substrate. Many TDs in the GaN film were observed on the FS and TS of Al2O3. However, few TDs were observed on the IS. Most of the TDs generated from the FS of Al2O3 were bent to the inclined facet rather than propagating to the GaN surface, resulting in a reduction in the dislocation density. Most of the TDs generated from the TS of Al2O3 were characterized as edge dislocations.

Very high cycle fatigue behavior of SAE52100 bearing steel by ultrasonic nanocrystalline surface modification.

In this paper, the SAE52100 bearing steel contained large quantities of cementite dispersed in ferrite matrix was subjected to the ultrasonic nanocrystalline surface modification (UNSM) treatment that aims for the extension of fatigue life. The microstructure and fatigue life of the untreated and treated specimens were studied by using electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM), and a developed ultra-high cycle fatigue test (UFT). After UNSM treatment, the coarse ferrite grains (- 10 µm) were refined to nanosize (- 200 nm), therefore, nanostructured surface layers were fabricated. Meanwhile, in the deformed layer, the number density and area fraction of cementite were increased up to - 400% and - 550%, respectively, which increased with the decrease in depth from the topmost treated surface. The improvement of hardness (from 200 Hv to 280 Hv) and high cycles fatigue strength by - 10% were considered the contribution of the developed nanostructure in the UNSM treated specimen.

Microstructural refinement of Al-Si alloy upon ultrasonic nanocrystalline surface modification treatment.

In this work, an Al-7 wt.% Si alloy, which is widely used as the structural materials in the automotive and aerospace industries for their high specific strength, was subjected to ultrasonic nanocrystalline surface modification (UNSM) treatment. After UNSM treatment, the effect of UNSM on the microstructural evolution of both Al grain and the dispersed Si particles was studied by using scanning electron microscope (SEM) and transmission electron microscope (TEM). Experimental results show that the ultra-fine grain (UFG, - 400 nm in size) structure is developed in the top surface layer (up to - 15 µm in depth). The coarse Si particles were refined and well dispersed in the UFG Al matrix. Cross-sectional TEM observation revealed that the grain refinement mechanism involved the formation of new grain boundaries dividing the coarse grain into UFG structure. Nanotwin and nanosize Si were formed within the original coarse Si particles. The presence of dispersed Si particles in the Al matrix accelerated the Al grain refinement process.

Surface nanocrystallization of pure Cu induced by ultrasonic shot peening.

Peening is mainly used as a method of surface treatment for microstructural modification in order to improve surface mechanical properties. The ultrasonic shot peening (USP) technique can cause severe plastic deformation with its high strain rate on the surface of metallic parts. However, systematic studies of microstructural refinement mechanism upon plastic deformation with consideration of alloy systems are rare. In this study, USP-treated Cu samples of 99.96% purity was examined using analytical techniques, Vickers microhardness test, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). Results of EBSD and microhardness analyses indicated grain refinement with deformation structures and hardness increase down to 400 µm in depth upon treatment. Depth specific TEM analysis of the samples revealed the steps of the grain refinement process to the formation of randomly oriented fine grains.

Restoration of rolling-contact-fatigued surfaces via nanoskin technology.

Rolling contact fatigue (RCF) is known as the dominant factor determining the service life of bearing materials. In this work, the fatigue life of the typical bearing alloy was significantly improved by introducing a nanoskin layer on the surfaces of the test specimens. The nanoskin layer structure was obtained by means of the ultrasonic nanocrystal surface modification (UNSM) technology. The microstructure of the nanoskin was analyzed via scanning electron microscope (SEM), electron back-scatter diffraction (EBSD), and transmission electron microscope (TEM). SUJ2 and SUJ3 bearings at different states of fatigue were subjected to UNSM treatment. For SUJ2 a rotary-bending fatigue (RBF) life average for three untreated specimens was chosen as 100% life, and then several untreated specimens were fatigued to 25%, 50% and 75% of life with subsequent UNSM treatment. This way used bearing conditions were simulated. The rotary-bending fatigue (RBF) tests of fatigue+UNSM SUJ2 specimens have shown 377-430% improvement of fatigue life, comparing to untreated specimens. For SUJ3 a RCF life untreated specimen was chosen as 100% life, and then several specimens were fatigued to approximately 100% of surface damage with subsequent UNSM treatment. Thus damaged surface conditions were simulated. The RCF tests of fatigue+UNSM SUJ3 specimens have shown 218% improvement of fatigue life, comparing to untreated specimens. This indicates the possibility of the restoration of the RCF life of bearing alloys by means of nanoskin treatment via UNSM technology.

Detection and determination of solute carbon in grain interior to correlate with the overall carbon content and grain size in ultra-low-carbon steel.

In this study, every effort was exerted to determine and accumulate data to correlate microstructural and compositional elements in ultra-low-carbon (ULC) steels to variation of carbon content (12-44 ppm), manganese (0.18-0.36%), and sulfur (0.0066-0.001%). Quantitative analysis of the ULC steel using optical microscope, scanning electron microscope, transmission electron microscope, and three-dimensional atom probe revealed the decrease of grain size and dislocation density with the increase of carbon contents and/or increase of the final delivery temperature. For a given carbon content, the grain interior carbon concentration increases as the grain size increases.

Effect of creep stress on the microstructure of 9-12% Cr steel for rotor materials.

High-chromium heat-resistant steel has been widely used as the key material to improve the condition of steam pressure and temperature in the modern high-efficiency power plants. Despite the use of the steel above 550°C for several decades, its major failure is owing to the creep fracture. In this study, the effect of creep stress on the microstructure in 9-12% Cr steel has been investigated microscopically, and it is clarified that the creep stress enhances precipitation of Laves phase and influences the lath width and dislocation density in lath interior.