Formation,evolution,reconstruction of black shales and their influence on shale oil and gas resource

Black shales are important products of material cycling and energy exchange among the lithosphere,atmosphere,hydrosphere,and biosphere.They are widely distributed throughout geological history and provide essential energy and mineral resources for the development of human society.They also record the evolution process of the earth and improve the understanding of the earth.This review focuses on the diagenesis and formation mechanisms of black shales sedimentation,composition,evolution,and reconstruction,which have had a significant impact on the formation and enrichment of shale oil and gas.In terms of sedimentary environment,black shales can be classified into three types:Marine,terrestrial,and marine-terrestrial transitional facies.The formation processes include mechanisms such as eolian input,hypopycnal flow,gravity-driven and offshore bottom currents.From a geological perspective,the formation of black shales is often closely related to global or regional major geological events.The enrichment of organic matter is generally the result of the interaction and coupling of several factors such as primary productivity,water redox condition,and sedimentation rate.In terms of evolution,black shales have undergone diagenetic evolution of inorganic minerals,thermal evolution of organic matter and hydrocarbon generation,interactions between organic matter and inorganic minerals,and pore evolution.In terms of reconstruction,the effects of fold deformation,uplift and erosion,and fracturing have changed the stress state of black shale reservoirs,thereby having a significant impact on the pore structure.Fluid activity promotes the formation of veins,and have changed the material composition,stress structure,and reservoir properties of black shales.Regarding resource effects,the deposition of black shales is fundamental for shale oil and gas resources,the evolution of black shales promotes the shale oil and gas formation and storage,and the reconstruction of black shales would have caused the heterogeneous distribution of oil and gas in shales.Exploring the formation mechanisms and interactions of black shales at different scales is a key to in-depth research on shale formation and evolution,as well as the key to revealing the mechanism controlling shale oil and gas accumulation.The present records can reveal how these processes worked in geological history,and improve our understanding of the coupling mechanisms among regional geological events,black shales evolution,and shale oil and gas formation and enrichment.

PRSS50-mediated inhibition of MKP3/ERK signaling is crucial for meiotic progression and sperm quality

Serine protease 50(PRSS50/TSP50)is highly expressed in spermatocytes.Our study investigated its role in testicular development and spermatogenesis.Initially,PRSS50 knockdown was observed to impair DNA synthesis in spermatocytes.To further explore this,we generated PRSS50 knockout(Prss50^(−/−))mice(Mus musculus),which exhibited abnormal spermatid nuclear compression and reduced male fertility.Furthermore,dysplastic seminiferous tubules and decreased sex hormones were observed in 4-week-old Prss50^(−/−)mice,accompanied by meiotic progression defects and increased apoptosis of spermatogenic cells.Mechanistic analysis indicated that PRSS50 deletion resulted in increased phosphorylation of extracellular signal-regulated protein kinases 1 and 2(ERK1/2)and elevated levels of MAP kinase phosphatase 3(MKP3),a specific ERK antagonist,potentially accounting for testicular dysplasia in adolescent Prss50−/−mice.Taken together,these findings suggest that PRSS50 plays an important role in testicular development and spermatogenesis,with the MKP3/ERK signaling pathway playing a significant role in this process.

Effect of Mn addition on microstructure and mechanical properties of GX40CrNiSi25-12 austenitic heat resistant steel

Three types of steels were designed on the basis of GX40CrNiSi25-12 austenitic heat resistant steel by adding different Mn contents(2wt.%,6wt.%,and 12wt.%).Thermodynamic calculation,microstructure characterization and mechanical property tests were conducted to investigate the effect of Mn addition on the microstructure and mechanical properties of the austenitic heat resistant steel.Results show that the matrix structure in all the three types of steels at room temperature is completely austenite.Carbides NbC and M_(23)C_(6)precipitate at grain boundaries of austenite matrix.With the increase of Mn content,the number of carbides increases and their distribution becomes more uniform.With the Mn content increases from 1.99%to 12.06%,the ultimate tensile strength,yield strength and elongation increase by 14.6%,8.0%and 46.3%,respectively.The improvement of the mechanical properties of austenitic steels can be explained by utilizing classic theories of alloy strengthening,including solid solution strengthening,precipitation strengthening,and grain refinement.The increase in alloy strength can be attributed to solid solution strengthening and precipitation strengthening caused by the addition of Mn.The improvement of the plasticity of austenitic steels can be explained from two aspects:grain refinement and homogenization of precipitated phases.

EphA2基因沉默对人食管癌EC9706细胞迁移、侵袭的影响及其机制研究

目的探讨促红细胞生成素产生肝细胞受体A2(EphA2)基因沉默对人食管癌EC9706细胞迁移、侵袭的影响及其作用机制。方法取对数生长期人食管癌EC9706细胞随机分为对照组、空载组及沉默组,分别转染Lipofectamine;2000、含无义随机序列(siRNA-NC-PGCsi3.0)和EphA2干扰序列(EphA2-siRNA-PGCsi3.0)质粒和脂质体的复合物。稳定转染后,Brd U法检测细胞增殖能力,划痕实验检测细胞迁移能力,Transwell小室实验检测细胞侵袭能力,qRT-PCR和Western blotting分别检测细胞中EphA2、Wnt1、β-连环蛋白(β-catenin)、E-钙黏蛋白(E-cadherin)、波形蛋白(Vimentin)mRNA及蛋白相对表达量。结果对照组、空载组、沉默组BrdU阳性率分别为(26.48±2.79)%、(23.52±2.57)%、(13.29±2.06)%,Brd U阳性率组间比较,差异有统计学意义(F=38.560,P=0.000)。与对照组、空载组比较,沉默组Brd U阳性率降低(P <0.05);对照组与空载组比较,差异无统计学意义(P>0.05)。对照组、空载组、沉默组细胞划痕愈合率分别为(83.16±8.31)%、(82.35±7.24)%、(34.24±5.27)%,细胞划痕愈合率组间比较,差异有统计学意义(F=78.869,P=0.000)。与对照组、空载组比较,沉默组细胞划痕愈合率降低(P <0.05);对照组与空载组比较,差异无统计学意义(P>0.05)。对照组、空载组、沉默组穿膜细胞数分别为(326.74±33.15)个、(331.27±34.59)个、(126.23±26.18)个,穿膜细胞数组间比较,差异有统计学意义(F=68.997,P=0.000),与对照组、空载组比较,沉默组穿膜细胞数减少(P <0.05);对照组与空载组比较,差异无统计学意义(P>0.05)。细胞中EphA2、Wnt1、β-catenin、Ecadherin、Vimentin mRNA相对表达量比较,差异有统计学意义(P <0.05),与对照组、空载组比较,沉默组Wnt1、β-catenin、Vimentin mRNA相对表达量降低(P <0.05),E-cadherin mRNA相对表达量升高(P <0.05)。对照组、空载组、沉默组细胞中EphA2、Wnt1、β-catenin、E-cadherin、Vimentin蛋白相对表达量比较,差异有统计学意义(P <0.05),与对照组、空载组比较,沉默组EphA2、Wnt1、β-catenin、Vimentin蛋白相对表达量降低(P <0.05),E-cadherin蛋白相对表达量升高(P <0.05)。对照组和空载组上述指标比较,差异无统计学意义(P>0.05)。结论 EphA2基因沉默对人食管癌EC9706细胞迁移和侵袭有一定的抑制作用,其机制可能与阻止Wnt/β-catenin信号通路相关。

Blood Lipid Profile and Prevalence of Dyslipidemia in Chinese Adults

To investigate the plasma lipid levels in a national representative sample of subjects and to determine the prevalence of dyslipidemia in the Chinese population. Methods Plasma lipid profile was analyzed using the data obtained during the Chinese national nutrition and health survey （CNHS） in 2002 which involved 14 252 participants at the age of 18 years or older. Results The mean levels of total cholesterol （TC）, triglyceride （TG） and high density lipoprotein cholesterol （HDL-C） in the participants were 3.81 retool/L, 1.10 mmol/L, and 1.30 mmol/L, respectively. In the groups of participants at the age of 18-44 years, 45-59 years, and over 60 years the mean TC level was 3.70 mmol/L, 4.09 mmol/L and 4.21 mmol/L, respectively, and the mean TG level was 07 mmol/L, 1.21 mmol/L, 1.20 mmol/L, 1.29 mmol/L, 1.33 mmol/L, and 1.33 mmol/L, respectively. The prevalence of dyslipidemia in Chinese adults was 18.6% and 22.2% in males and 15.9% in females. Dyslipidemia prevalence was higher in urban districts than in rural areas （21.0% vs. 17.7%）. The prevalence of hypercholesterolemia, hypertriglyceridemia, and low HDL cholesterol was 2.9%, 11.9%, and 7.4% respectively among the participants. Conclusion Dyslipidemia has become one of the important health risk factors in the Chinese population. There is no significantly difference in the prevalence of dyslipidemia between the groups of participants at the age of 45-59 years and over 60 years. This study provides important lipid profile data for policy making and guideline development for the prevention of dyslipidemia in the Chinese population.

Relationship of Body Mass Index, Waist Circumference and Cardiovascular Risk Factors in Chinese Adult

Objective To compare the relative risk of waist circumference （WC） and/or BMI on cardiovascular risk factors. Methods A cross-sectional data of 41 087 adults （19 567 male and 21 520 female） from the 2002 China National Nutrition and Health Survey were examined. According to the obesity definition of WGOC （BMI, 24 kg/m^2 and 28 kg/m^2; WC, male 85 cm and 95 cm for male, 80 cm and 90 cm for female）, the study population were divided into 9 groups. The prevalence and odds ratio （ORs） of cardiovascular disease （CVD） risk factors （hypertension, high fasting plasma glucose and dyslipidemia） were compared among these 9 groups. Stepwise linear regression analyses were used to compare the likelihood of BMI and/or WC on CVD risk factors. Results Both the indexes levels and the odds ratios of CVD risk factors were significantly increased （decreased for HDL-C levels） along with the increase of WC and/or BMI, even when the effect of age, sex, income, education, sedentary activity and dietary factors were adjusted. The variances （R2） in CVD risk factors explained by WC only and BMI only were quite similar, but a little bit larger when WC and BMI were combined. The standard fl was higher of BMI when predicting systolic BP and was higher of WC when predicting TG, TC and HDL. Conclusions BMI and WC had independent effects on CVD risk factors and combination of BMI and WC would be more predictive. Findings from the present study provided substantive evidence for the WGOC recommendation of a combined use of BMI and WC classifications.

Report on Childhood Obesity in China (2) Verification of BMI Classification Reference for Overweight and Obesity in Chinese Children and Adolescents

Objective To verify Working Group for Obesity in China （WGOC） recommended body mass index （BMI） classification reference for overweight and obesity in Chinese children and adolescents using the data of 2002 China Nationwide Nutrition and Health Survey. Methods PediaWic metabolic syndrome （MetS） and abnormality of each risk factor for MetS were defined using the criteria for US adolescents. Definition of hyper-TC, LDL, and dyslipidemia in adults was applied as well. The average level and abnormality rate of the metabolic indicators were described by BMI percentiles and compared with general linear model analysis. Receiver operating characteristic analysis was used to summarize the potential of BMI to discriminate between the presence and absence of the abnormality of these indicators. Results There was neither significantly increasing nor significantly decreasing trend of biochemical parameter levels in low BMI percentile range （〈65th）. Slight increasing trend from the 75th and a significant increase were found when BMI≥85th percentile. In general, the prevalence of the examined risk factors varied slightly when BMI percentile〈75th, and substantial increases were consistently seen when BMI percentile≥75th. As an indicator of hyper-TG, hypertension and MetS, the sensitivity and specificity were equal at the point of BMI〈75th percentile, and the Youden＇s index of risk factors also reached peak point before 75th percentile except for MetS. When the BMI percentile was used as the screening indicator of MetS, Youden＇s index reached peak point at 85th percentile, just the point in the ROC graph that was nearest to the upper left comer. Conclusion The BMI classification reference for overweight and obesity recommended by WGOC is rational to predict and prevent health risks in Chinese children and adolescents. Lower screening cut-off points, such as 83th percentile or 80th percentile, should not be excluded when they are considered as overweight criteria in future intervention or prevention studies.

Porosity model and pore evolution of transitional shales:an example from the Southern North China Basin

The evolution of shale reservoirs is mainly related to two functions:mechanical compaction controlled by ground stress and chemical compaction controlled by thermal effect.Thermal simulation experiments were conducted to simulate the chemical compaction of marine-continental transitional shale,and X-ray diffraction(XRD),CO2 adsorption,N2 adsorption and high-pressure mercury injection(MIP)were then used to characterize shale diagenesis and porosity.Moreover,simulations of mechanical compaction adhering to mathematical models were performed,and a shale compaction model was proposed considering clay content and kaolinite proportions.The advantage of this model is that the change in shale compressibility,which is caused by the transformation of clay minerals during thermal evolution,may be considered.The combination of the thermal simulation and compaction model may depict the interactions between chemical and mechanical compaction.Such interactions may then express the pore evolution of shale in actual conditions of formation.Accordingly,the obtained results demonstrated that shales having low kaolinite possess higher porosity at the same burial depth and clay mineral content,proving that other clay minerals such as illite-smectite mixed layers(I/S)and illite are conducive to the development of pores.Shales possessing a high clay mineral content have a higher porosity in shallow layers(<3500 m)and a lower porosity in deep layers(>3500 m).Both the amount and location of the increase in porosity differ at different geothermal gradients.High geothermal gradients favor the preservation of high porosity in shale at an appropriate Ro.The pore evolution of the marine-continental transitional shale is divided into five stages.Stage 2 possesses an Ro of 1.0%-1.6%and has high porosity along with a high specific surface area.Stage 3 has an Ro of 1.6%-2.0%and contains a higher porosity with a low specific surface area.Finally,Stage 4 has an Ro of 2.0%-2.9%with a low porosity and high specific surface area.

Association between Adiponectin and Metabolic Syndrome in Older Adults from Major Cities of China

Objective To investigate the association between adiponectin and metabolic syndrome （MetS） and related diseases in older adults from major cities of China. Methods A total of 2 049 adults at the age of 60-96 years from18 major cities of China were enrolled in the study. Plasma adiponectin and insulin concentrations were measured. Insulin resistance was assessed by homeostasis model assessment of insulin resistance （HOMA-IR）. The definitions proposed by International Diabetes Federation （IDF） and American Heart Association/National Heart, Lung, and Blood/nstitute （AHA/NLHBI） were used to identify MetS. Results The adiponectin concentration increased with the advance of age and was higher in women than in men. The sex specific adiponectin concentration was inversely correlated with body mass index （BMI）, waist circumference, diastolic blood pressure, triglycerides, glucose and fasting blood insulin, and positively correlated with HDL-C （P〈0.001）. The adiponectin concentration decreased with increasing MetS components. Compared with the 4th sex-specific adiponectin quartile, the odds ratio （OR） for prevalent MetS-IDF and MetS-AHA/NLHBI in subjects of the 1st quartile group was 3.25 （95% CI： 2.24, 4.71） and 3.21 （95% CI： 2.26, 4.55）, respectively. The association was independent of age, sex, life-style factors, medication, family history of chronic diseases, BMI, and HOMA-IR, The OR for MetS was much higher than those of MetS components and its related diseases. Conclusion Adiponectin is strongly associated with MetS independent of insulin resistance and obesity in older adults from major cities in China. The adiponectin concentration is a useful predictor for the risk of MetS.

Preparation of Monoclonal Antibody Against HPT and Its Application to Detecting Marker Protein in Genetically Modified Rice

To produce the monoclonal antibodies （mAbs） against hygromycin B phosphotransferase （HPT） and to develop immunoassay based on mAbs for biosafety assessment of HPT in genetically modified rice （GM rice）. Methods BALB/c mice were immunized with purified recombinant 6His. HPT protein, and the conventional hybridoma technology was used to generate the monoclonal hybridoma cells. ELISA and Western blot were used to analyze the specificity of mAbs recognizing HPT and the cross reaction with other proteins. A double-Ab sandwich ELISA method was established to detect HPT expression level in the sck gene-modified rice plants. Results Four hybridomas, named F1,D4-2, D4-4, and D4-5, producing the mAbs against HPT were successfully obtained with the titer of ascetic mAbs ranging from 10×10^-4 to10×10^-5. Identification of subclass showed that all the produced mAbs belonged to IgG1. Western blot showed specific binding reaction between the mAbs to the HPT proteins expressed in the GM rice. A double sandwich ELISA coated with anti-HPT polyclonal antibody was established with mAbs as sandwich antibody, which showed a sensitivity of 30ng/mL and did not crossreact with other proteins. The expression level of HPT in the leaves of sck-transformed lines was detected （80-150ng/mL）. But HPT protein in the grain and seed of GM rice could not be detected using this ELISA assay, Conclusion Anti-HPT mAbs prepared herein have a high specificity and can be used for rapid assay of HPT antigen. The expression level of HPT in the GM rice grain and seed is lower than our ELISA detection limit.

Purification and Immunity Analysis of Recombinant 6His-HPT Protein Expressed in E.coli

To obtain HPT protein (Hygromycin B Phosphotransferase), a kind of plant selective maker gene product expressed from E.coli and to prepare the polyclonal antibody (pAbs) against it. Methods HPT cDNA fragment was obtained by PCR and was inserted into the prokaryotic expressing vector pBV222. Then the constructed recombinant plasmid pBV222-HPT was transfered into E.coli DH5?for HPT expression. The recombinant expressing system was confirmed by restriction endonuclease digestion, DNA sequencing and protein expression. E.coli cells were lysed by sonication and detergent dissolution. After cell membrane was extracted, the inclusion bodies were denatured by 8 mol/L Urea and purified with metal chelate affinity chromatography on Ni-NTA agarose under denaturing condition. The purified 6His-HPT was characterized by SDS-PAGE, and used to immunize rabbit. The titer and specificity of antisera were detected by ELISA and Western blot respecitively. Results Analysis of DNA sequence and restricted enzymes showed that the sequence of PBV222-HPT plasmid was correct. The amount of recombinant HPT expressed in E.coli accounted for 30% of total cellular proteins. From 1 liter of fermentative bacteria about 22 milligrams of pure recombinant HPT was isolated with purity above 95%. The recombinant HPT protein could produce high titer antiserum in rabbits and show good immunity activity. Western blot showed specific binding reaction between the antiserum to the purified 6His-HPT protein and their expressed products (plants protein and bacterial protein). Conclusion HPT protein can be expressed and purified from E.coli by a relatively simple method, which has high immunity activity.

Low-cycle fatigue behavior of DZ125 superalloy under prior exposure conditions

Low-cycle fatigue(LCF) behavior of the directionally solidified(DS) nickel-based DZ125 superalloy was studied at elevated temperature(980 ℃).Specimens were,respectively,exposed for 0,2,25,50,and 100 h in air.The fatigue life of pre-exposed specimens is lower than that of unexposed specimens.The result is closely associated with fatigue crack initiation and propagation due to oxygen embrittlement and cycle loading.Detailed fractographic evaluations indicate the fatigue life is closely related to the surface microstructural modification.The resulting changes in microstructure cause the decrease in the effective area and the increase in actual stress.A methodology based on the continuum damage mechanics is developed to describe the correlation between the residual LCF life and pre-exposed time.

Applications of AI in advanced energy storage technologies

The prompt development of renewable energies necessitates advanced energy storage technologies,which can alleviate the intermittency of renewable energy.In this regard,artificial intelligence(AI)is a promising tool that provides new opportunities for advancing innovations in advanced energy storage technologies(AEST).Given this,Energy and AI organizes a special issue entitled“Applications of AI in Advanced Energy Storage Technologies(AEST)”.

Evaluation of service-induced microstructural damage for directionally solidified turbine blade of aircraft engine

Turbine blades of gas turbine engines usually suffer from severe operational conditions characterized by high temperature and stress. Severe operational conditions during service cause microstructural changes in turbine blades and degrade their mechanical properties. In this study, service-induced microstructural damages in serviced turbine blades manufactured from a directionally solidified superalloy were evaluated. The observed microstructural damage of the turbine blade mainly involves the coarsening and rafting of γ' precipitates. The leading edge of 60% height of the turbine blades undergone most severe microstructural damage with significant microstructural evolution at this area. Microstructural damage affects the mechanical properties such as Vickers hardness, that is,Vickers hardness decreases as the equivalent diameter decreases. Microstructural damage shows great positiondependent feature as service temperature and radial stress on blade changes. With the aid of energy-dispersive spectrometer(EDS) analysis on carbide, the transformation of carbide does not exist. In addition, no topological closed-packed phase exists in the turbine blade.

Low-cycle fatigue behavior of a directionally solidified Ni-based superalloy subjected to gas hot corrosion pre-exposure

The influence of gas high-temperature hot corrosion(HTHC) pre-exposure on low-cycle fatigue(LCF)behavior was characterized for the directionally solidified(DS) Ni-based superalloy DZ125. Fatigue tests were carried out at 850 ℃ in the pre-exposed and unexposed specimens for 2, 15 and 25 h. Experimental results show that the porous corrosion scale and γ′-depleted layer formed in gas hot corrosion condition alter the crack initiation mechanisms of the superalloy. Fatigue cracks of the pre-exposed specimens originate from multiple surface locations where spalling of the corrosion products occur,while nucleation of unexposed specimen begins in the defects close to the surface. There is a significant reduction in LCF behavior for pre-exposed specimens in comparison with unexposed specimens.

Constitutive modeling of a directionally solidified nickel-based superalloy DZ125 subjected to thermal mechanical creep fatigue loadings

A transversely isotropic continuum elasto-viscoplasticity model,which was developed from Chaboche’s unified constitutive model,was formulated to capture the thermal mechanical creep fatigue deformation behavior of a directionally solidified nickel-based superalloy.A fourthorder tensor was introduced to model material anisotropy.In order to model the tertiary creep behavior,the Kachanov damage evolution equation was coupled into the stress tensor.Based on the test results of uniaxial tensile,fatigue,and creep loadings at isothermal temperature conditions,the material parameters are obtained.Thermal mechanical fatigue(TMF) and creep-fatigue interaction test results were used to verify the robustness of the model.Additionally,strain-temperature-dependent stress-strain responses under TMF loadings were analyzed using the present model.Under strain-controlled conditions,both of the stress ranges and mean stresses are strongly influenced by the strain-temperature phases,a key parameter for TMF tests.

Fatigue behavior of uncoated and MCrAlY-coated DS nickelbased superalloys pre-exposed in hot corrosion condition

The effects of a MCrAlY coating on low-cycle fatigue(LCF) behavior of directionally solidified(DS)nickle-based superalloy DZ125 were investigated. Before the fatigue testings, the specimens were pre-exposed in high-temperature hot corrosion(HTHC) environment generating by a burner rig at 850 ℃. The results show that the coating in hot corrosion condition has beneficial effects on the fatigue resistance of superalloy. Under corrosion condition, the MCrAlY-coated specimens tested have higher fatigue lives than the uncoated specimens at the same stress level. The coating failure results from fatigue process and numerous fatigue cracks were nucleated at the specimen surface, only one main crack propagates inward and the secondary cracks away from the fracture surface are perpendicular to the loading orientation.

A physically based methodology for predicting anisotropic creep properties of Ni-based superalloys

This paper is focused on developing suitable methodology for predicting creep characteristics （i.e., the minimum creep strain rate, stress rupture life and time to a specified creep strain） of typical Ni-based directionally solidified （DS） and single-crystal （SC） superalloys. A modem method with high accuracy on simulating wide ranging creep properties was fully validated by a sufficient amount of experimental data, which was then developed to model anisotropic creep characteristics by introducing a simple orientation factor defined by the ultimate tensile strength （UTS）. Physical confidence on this methodology is provided by the well-predicted transitions of creep defor- mation mechanisms. Meanwhile, this method was further adopted to innovatively evaluate the creep properties of different materials from a relative perspective.

High-temperature oxidation behavior of DZ125 Ni-based superalloy under tensile stress

The key in antioxidant capacity of aero-engine hot components is the protective oxide scales.Many factors can affect the performance of oxide scales.The effect of tensile stress on high-temperature oxidation behavior of directionally solidified DZ125 Ni-based superalloy was investigated by thermogravimetric analysis(TGA).Tensile samples were subjected to stress of 100 MPa,and the oxidation behavior was studied at 980℃in air.The surface and cross-sectional morphologies of the oxidized coating were analyzed by scanning electron microscope(SEM).The influence of tensile stress on the oxidation behavior of directionally solidified DZ125 Ni-based superalloy at high temperature was discussed.Results show that an applied tensile stress generally leads to larger Cr/Ni mass ratio in the oxide scales,greater overall chromium depletion values directly under the oxide scales,lower specific weight gain values and thinner oxide scales.These factors are attributed to the formation of fast diffusion paths for Cr atoms to diffuse to the surface under tensile stress,thus causing a reduction in the duration of the less protective transient oxidation period and promoting a faster formation of the protective Cr_(2)O_(3)layer.

Oxidation-induced damage of an uncoated and coated nickel-based superalloy under simulated gas environment

Turbine blades and vans operated in an aggressive gas environment usually suffer from combined oxidation and cycle loading effects. The surface oxide layer will result in premature failure and lead to a significant reduction in the service lifetime. The effects of prior oxidation-induced damage under a simulated combustion-gas environment on the fatigue lifetime of the directionally solidified（DS） nickel-based superalloy DZ125 with and without an oxidation-resistant coating were presented. The fatigue lifetime of uncoated samples is adversely affected by prior oxidation exposure. The deterioration of fatigue lifetime in uncoated samples is associated with surface microstructural degradation, which occurs during prior exposure. However,the presence of MCrAlY coating is beneficial for the sample＇s lifetime under high stress. Further scanning electron microscopy（SEM） analysis demonstrates that the coating does not contribute to the initiation mode of fatigue cracks.