Alumina ceramics are crucial for high-performance applications,such as turbine blades,due to their excellent thermal stability and mechanical properties.However,existing fabrication methods often fail to balance stren...Alumina ceramics are crucial for high-performance applications,such as turbine blades,due to their excellent thermal stability and mechanical properties.However,existing fabrication methods often fail to balance strength,porosity,and dimensional precision.This study partially fills this research gap through a systematic investigation of calcium oxide(CaO)doping effects on alumina ceramic cores fabricated via ceramic stereolithography,with controlled doping ratios and sintering parameters.A ceramic paste was prepared using coarse and fine Al_(2)O_(3) particles mixed with CaO as a sintering aid,followed by debinding and sintering to achieve optimal mechanical properties.The results show that CaO doping significantly enhances the fiexural strength of alumina cores while maintaining porosity levels between 20%and 30%and controlling the sintering shrinkage rate to about 5%.Additionally,CaO doping alters the microstructure by inhibiting the transformation of spherical fine particles into fiaky grains,improving sintering activity.However,as the CaO doping content increases,the bending strength increases,while the shrinkage rate of the material also tends to increase,resulting in a reduction in the overall porosity.This has a negative impact on the control of the manufacturing precision of turbine blades.Thus,although CaO doping improves strength and microstructure,achieving necessary dimensional control requires further optimization of doping content and sintering conditions.展开更多
Ceramic cores are important in the fabrication of superalloy hollow blades,which are increasingly characterized by intricate internal cavity channels.This complexity poses significant challenges to traditional manufac...Ceramic cores are important in the fabrication of superalloy hollow blades,which are increasingly characterized by intricate internal cavity channels.This complexity poses significant challenges to traditional manufacturing processes.The vat photopolymerization 3D printing technology provides a new choice for ceramic cores with complex structures.However,the lamellar structure of the vat photopolymerization 3D printed ceramic cores leads to the anisotropy.Meanwhile,the low strength and high shrinkage of ceramic cores restrict their industrial application.In this study,using Al_(2)O_(3)powder as the main material,the effects of zircon content on the sintering shrinkage,open porosity,fiexural strength,and other properties of Al_(2)O_(3)-based ceramic cores were studied to address the aforementioned issues.The influencing mechanism of zircon distribution on sintering shrinkage was analyzed,and the strengthening mechanism of mullite on ceramic cores was discussed from both thermodynamics and dynamics aspects.Through the comprehensive evaluation of ceramic core properties,the Al_(2)O_(3)-based ceramic core with 15vol.%zircon exhibites the optimal performance.Compared with the core samples without zirconium addition,the fiexural strength of the Al_(2)O_(3)-based ceramic core with 15vol.%zircon increases from 14.80 MPa to 61.54 MPa at 25°C,an increase of 315.8%;and from 4.91 MPa to 11.59 MPa at 1,500°C,an increase of 136.0%.The shrinkage in the Z-axis is reduced by 21%,which better weakens the anisotropy of the shrinkage of 3D printed Al_(2)O_(3)-based ceramic cores.ZrO_(2)phase and mullite phase are formed by zircon,which improve the comprehensive properties of Al_(2)O_(3)-based ceramic cores.The successful 3D printing of high-performance Al_(2)O_(3)-based ceramic cores via vat photopolymerization has promoted its industrial application for fabricating ceramic cores with complex structures.展开更多
Ceramic cores are key components in the production of castings with complex cavity structures. With the continuous development of the aerospace field, the demand for the castings with complex cavity structures is incr...Ceramic cores are key components in the production of castings with complex cavity structures. With the continuous development of the aerospace field, the demand for the castings with complex cavity structures is increasing. When using insoluble ceramic cores for casting, there is a significant challenge in removing complex blind cavities, which severely affects the completeness of the shape of the castings. Soluble ceramic cores can disintegrate when placed in water, greatly simplifying the removal process of cores and ensuring the complete formation of castings with complex cavity structures. Additive manufacturing technology, compared to traditional methods for preparing the soluble ceramic cores, does not require molds and can achieve direct forming of complex cores, simplifying the preparation process and reducing production time and costs. Nowadays, various additive manufacturing technologies, such as stereolithography(SL), selective laser sintering(SLS), direct ink writing(DIW), and binder jetting(BJ) technologies, have been successfully applied to the preparation of the ceramic cores. This paper analyzed the advantages and limitations of various additive manufacturing technologies, reviewed the research progress and raw material classifications of soluble ceramic cores prepared by these technologies, and looked forward to the future developments in the preparation of soluble ceramic cores using additive manufacturing technologies.展开更多
The complex ceramic core used for hollow turbine blades requires a high porosity and a high fiexural strength. For a better balance between porosity and fiexural strength, ceramic materials with porous structures are ...The complex ceramic core used for hollow turbine blades requires a high porosity and a high fiexural strength. For a better balance between porosity and fiexural strength, ceramic materials with porous structures are preferred. In order to achieve the transition from disordered pore formation to ordered pore formation, Al_(2)O_(3) ceramic cores with triply periodic minimal surface(TPMS) micro lattice structures with different structural configurations(gyroid, diamond, and neovius) and different volume fractions of lattice structures(30, 40, and 50, vol.%) were designed and prepared by vat photopolymerization 3D printing. The effects of structural configuration and volume fraction of the lattice structure on the following structural shrinkage, microstructure, and flexural strength were investigated. The shrinkage relationship of the three lattice configurations is: neovius>diamond>gyroid. Besides, it is found that with an increase in the volume fraction of the 3D printed Al_(2)O_(3) ceramic micro lattice structures, their fiexural strength correspondingly increases ranging from 54.95 MPa to 139.1 MPa. The maximum average fiexural strength of the 3D printed Al_(2)O_(3) ceramic micro lattice structures is obtained when the structural configuration is diamond and with a volume fraction of 50vol.%, which is 139.1 MPa. Even when the volume fraction of the lattice structure is 30vol.%, that is to say the porosity is 70%, the fiexural strength is as high as 50-70 MPa, which can still be maintained at a high level. In addition, when the volume fraction of the lattice structure is a certain value, the sample with diamond configuration has a higher strength. The internal pore morphology, pore size, and porosity of the cores are precisely controlled, achieving both a high porosity and a high strength. Therefore, this study maintains high porosity and high strength simultaneously, providing a new lattice structure design idea for 3D printed ceramic cores.展开更多
Ceramic cores are key to forming a cooling structure within the hollow blade cavities.The use of stereolithography(SL)3D printing technology eliminates the need for moulds,facilitating the preparation of complex-shape...Ceramic cores are key to forming a cooling structure within the hollow blade cavities.The use of stereolithography(SL)3D printing technology eliminates the need for moulds,facilitating the preparation of complex-shaped ceramic cores.In this study,silica-based ceramic cores incorporating nano-3YSZ(3mol.% yttria stabilised zirconia)and micron-sized Y_(2)O_(3) were prepared via SL 3D printing ceramic technology to promote the formation of cristobalite and ZrSiO_(4),thereby improving the high-temperature properties.The flexural strength at 25℃ and 1,500℃,deflection at 1,500℃,shrinkage rate,and porosity of the core samples sintered at different temperatures(1,170℃,1,185℃,1,200℃,1,215℃,and 1,230℃)were tested and investigated.The mechanism underlying the high temperature performance of the cores was elucidated through analysis of cross-sectional morphology,element distribution,and phase constitution of the samples.As the sintering temperature increases,the shrinkage and flexural strength at 25℃ of the core rise,while the open porosity and deflection at 1,500℃ decrease.When the sintering temperature reaches 1,200℃ or higher,the 1,500℃ flexural strength can be measured,which increases as the sintering temperature rises.The core exhibits excellent creep resistance when sintered at temperatures of 1,200℃ and above.Considering the comprehensive performance requirements for the core,the sintering temperature of 1,200℃ was selected.At the sintering temperature of 1,200℃,the core exhibits shrinkage rates of 3.76%(X),3.38%(Y),and 3.95%(Z),alongside a flexural strength of 9.01 MPa at 25℃ and 32.15 MPa at 1,500℃,and an open porosity of 26.39%.The deflection of the core at 1,500℃ is 0.15 mm,which helps to maintain the dimensional stability of the ceramic core during casting.XRD results indicate that samples fractured after 25℃ flexural strength test still contain amorphous quartz glass,alongside substantial quantities of yttria stabilized zirconia and Y_(2)O_(3).Samples fractured after 1,500℃ flexural strength test exhibit significant crystallisation of amorphous quartz glass into cristobalite,with silica and 3YSZ combining to form ZrSiO_(4).Y_(2)O_(3) as a network modifier of the glass network destroys the bridging oxygen in the silica-oxygen bond,thereby reducing the energy required for glass crystallisation and promoting the crystallisation reaction of quartz glass to form cristobalite.In addition,nano-3YSZ combines with SiO_(2) at high temperatures to form ZrSiO_(4).Since cristobalite and ZrSiO_(4) are crystals,both of them have strong creep resistance,thus improving the high temperature flexural strength and deformation resistance of the ceramic cores.展开更多
To meet the evolving demands of aeroengine development,the structural and performance requirements for ceramic cores have become increasingly stringent.Vat photopolymerization 3D printing,owing to its moldless,fiexibl...To meet the evolving demands of aeroengine development,the structural and performance requirements for ceramic cores have become increasingly stringent.Vat photopolymerization 3D printing,owing to its moldless,fiexible manufacturing,and other advantages,demonstrates significant potential in the preparation of ceramic cores with intricate structures.However,its practical application still faces multiple challenges,including layered structures and property anisotropy,defects such as cracks and collapse during printing and sintering,forming inaccuracies,and difficulties in controlling surface roughness.Recent advances have focused on optimizing slurry formulation and rheology,improving curing behavior,introducing auxiliary powders and additives,tailoring forming parameters,and optimizing the sintering process.Nevertheless,effectively suppressing lamellar defects,achieving superior dimensional accuracy,and maintaining high surface quality in complex structures remain the core scientific and technical issues to be solved.Future research should concentrate on refining curing mechanisms,advancing powder design and organic system optimization,and regulating the coupled processes of forming,debinding,and sintering to accelerate the application of VPP 3D printed ceramic cores in aerospace manufacturing.展开更多
Protoporphyrin Ⅸ(PPⅨ), a basic porphyrin system found in nature, all “porphyrin-type”tetrapyrroles with a biological function are biosynthetically derived thereof. PPⅨ is a metalloprosthetic group of numerous pro...Protoporphyrin Ⅸ(PPⅨ), a basic porphyrin system found in nature, all “porphyrin-type”tetrapyrroles with a biological function are biosynthetically derived thereof. PPⅨ is a metalloprosthetic group of numerous proteins involved in diverse metabolic and respiratory processes across all domains of life, and is thus considered essential for respiring organisms. Determining the biotic and abiotic factors that influence marine microbial growth and community structure is critical for understanding global biogeochemical cycles. Here,we present vertical profiles of intracellular PPⅨ and four derivative products(Chlorophylla/b and Pheophytin-a/b) from two coastal sediment cores, alongside ancillary geochemical and 16S rRNA microbial community data. Our findings indicated that PPⅨ is present in the natural sediment environment and displays a decreasing trend with depth, revealing a significant positive correlation with both organic matter and microbial abundance. Cooccurrence networks revealed that the environmental distribution of PPⅨ was positively correlated with the microbial porphyrin producer(high genetic completeness), but negatively correlated with auxotrophs(absence or low genetic completeness). It emphasized the critical role of PPⅨ as a biological molecule involved in key physiological processes. These results suggest that PPⅨ is a prominent component of the shared extracellular metabolite pool, especially in anoxic marine sediments where it exists at physiologically relevant concentrations for microbial metabolism. This study highlighted the significance of PPⅨ in microbial ecology and its potential impact on biogeochemical cycles in marine sedimentary environments.展开更多
Aimed at the long and narrow geometric features and poor generalization ability of the damage detection in conveyor belts with steel rope cores using the X-ray image,a detection method of damage X-ray image is propose...Aimed at the long and narrow geometric features and poor generalization ability of the damage detection in conveyor belts with steel rope cores using the X-ray image,a detection method of damage X-ray image is proposed based on the improved fully convolutional one-stage object detection(FCOS)algorithm.The regression performance of bounding boxes was optimized by introducing the complete intersection over union loss function into the improved algorithm.The feature fusion network structure is modified by adding adaptive fusion paths to the feature fusion network structure,which makes full use of the features of accurate localization and semantics of multi-scale feature fusion networks.Finally,the network structure was trained and validated by using the X-ray image dataset of damages in conveyor belts with steel rope cores provided by a flaw detection equipment manufacturer.In addition,the data enhancement methods such as rotating,mirroring,and scaling,were employed to enrich the image dataset so that the model is adequately trained.Experimental results showed that the improved FCOS algorithm promoted the precision rate and the recall rate by 20.9%and 14.8%respectively,compared with the original algorithm.Meanwhile,compared with Fast R-CNN,Faster R-CNN,SSD,and YOLOv3,the improved FCOS algorithm has obvious advantages;detection precision rate and recall rate of the modified network reached 95.8%and 97.0%respectively.Furthermore,it demonstrated a higher detection accuracy without affecting the speed.The results of this work have some reference significance for the automatic identification and detection of steel core conveyor belt damage.展开更多
For the first time,the linear and nonlinear vibrations of composite rectangular sandwich plates with various geometric patterns of lattice core have been analytically examined in this work.The plate comprises a lattic...For the first time,the linear and nonlinear vibrations of composite rectangular sandwich plates with various geometric patterns of lattice core have been analytically examined in this work.The plate comprises a lattice core located in the middle and several homogeneous orthotropic layers that are symmetrical relative to it.For this purpose,the partial differential equations of motion have been derived based on the first-order shear deformation theory,employing Hamilton’s principle and Von Kármán’s nonlinear displacement-strain relations.Then,the nonlinear partial differential equations of the plate are converted into a time-dependent nonlinear ordinary differential equation(Duffing equation)by applying the Galerkin method.From the solution of this equation,the natural frequencies are extracted.Then,to calculate the non-linear frequencies of the plate,the non-linear equation of the plate has been solved analytically using the method of multiple scales.Finally,the effect of some critical parameters of the system,such as the thickness,height,and different angles of the stiffeners on the linear and nonlinear frequencies,has been analyzed in detail.To confirmthe solution method,the results of this research have been compared with the reported results in the literature and finite elements in ABAQUS,and a perfect match is observed.The results reveal that the geometry and configuration of core ribs strongly affect the natural frequencies of the plate.展开更多
The dependence of elastic moduli of shales on the mineralogy and microstructure of shales is important for the prediction of sweet spots and shale gas production. Based on 3D digital images of the microstructure of Lo...The dependence of elastic moduli of shales on the mineralogy and microstructure of shales is important for the prediction of sweet spots and shale gas production. Based on 3D digital images of the microstructure of Longmaxi black shale samples using X-ray CT, we built detailed 3D digital images of cores with porosity properties and mineral contents. Next, we used finite-element （FE） methods to derive the elastic properties of the samples. The FE method can accurately model the shale mineralogy. Particular attention is paid to the derived elastic properties and their dependence on porosity and kerogen. The elastic moduli generally decrease with increasing porosity and kerogen, and there is a critical porosity （0.75） and kerogen content （ca. ≤3%） over which the elastic moduli decrease rapidly and slowly, respectively. The derived elastic moduli of gas- and oil-saturated digital cores differ little probably because of the low porosity （4.5%） of the Longmaxi black shale. Clearly, the numerical experiments demonstrated the feasibility of combining microstructure images of shale samples with elastic moduli calculations to predict shale properties.展开更多
This paper focuses on some key problems in web community discovery and link analysis.Based on the topic-oriented technology,the characteristics of a bipartite graph are studied.An Х bipartite core set is introduced t...This paper focuses on some key problems in web community discovery and link analysis.Based on the topic-oriented technology,the characteristics of a bipartite graph are studied.An Х bipartite core set is introduced to more clearly define extracting ways.By scanning the topic subgraph to construct Х bipartite graph and then prune the graph with i and j ,an Х bipartite core set,which is also the minimum element of a community,can be found.Finally,a hierarchical clustering algorithm is applied to many Х bipartite core sets and the dendrogram of the community inner construction is obtained.The correctness of the constructing and pruning method is proved and the algorithm is designed.The typical datasets in the experiment are prepared according to the way in HITS（hyperlink-induced topic search）.Ten topics and four search engines are chosen and the returned results are integrated.The modularity,which is a measure of the strength of the community structure in the social network,is used to validate the efficiency of the proposed method.The experimental results show that the proposed algorithm is effective and efficient.展开更多
Vat photopolymerization(VPP)3D printing is an optimized technology for complex-shaped ceramic cores,in which the solid loading of ceramic slurries greatly infiuences the microstructure and property of the final cerami...Vat photopolymerization(VPP)3D printing is an optimized technology for complex-shaped ceramic cores,in which the solid loading of ceramic slurries greatly infiuences the microstructure and property of the final ceramic parts.However,the high solid loading of slurries is highly limited by the high viscosity.In this study,silica-based ceramic core slurries with solid loading up to 68vol.%were achieved by the composition design to optimize the performance,considering the curing,rheological,and double bond conversion rate.The slurries demonstrate superior curing and rheological performance with mass ratio of monomers being 3:2 and mass fraction of BYK111 being 4wt.%.Afterwards,the impact of solid loading on the morphology and mechanical properties was investigated.As the solid loading increases,the microstructure becomes gradually dense,leading to an improved flexural strength of 19.5 MPa.Additionally,the sintering shrinkage becomes more uniform,satisfying the casting requirements effectively.This work serves as a guide for the preparation of ceramic slurries with a high solid loading.展开更多
Ceramic cores fabricated by stereolithography exhibit great potential in casting turbine blades.Previous research on ceramic core molding was primarily conducted using vertical printing techniques,which not only resul...Ceramic cores fabricated by stereolithography exhibit great potential in casting turbine blades.Previous research on ceramic core molding was primarily conducted using vertical printing techniques,which not only resulted in lengthy molding durations but also compromised the mechanical strength.In this work,silica(SiO--_2)ceramic cores,with fine complex geometric shapes,were fabricated using 65vol.%ceramic slurry by digital light processing(DLP)with different printing angles.Printing angles significantly impact the surface accuracy,shrinkage,printing efficiency of green bodies,as well as the microstructure and mechanical properties of sintered ceramic core samples.As the printing angle in the green body increases,the bonding area decreases,surface roughness on the XY plane worsens,shrinkage in the Z direction becomes more pronounced,and the printing efficiency declines.Similarly,an increase in the printing angle in the sintered body leads to a reduction in bending strength.At a printing angle of 30°,the printing time is reduced to half of that at 90°,which improves the molding efficiency.Meanwhile,the obtained bulk density of 1.71 g·cm~(-3),open porosity of 24%,and fiexural strength of 10.6±1 MPa can meet the requirements of sintered ceramic cores.Therefore,designing and optimizing the printing angles can achieve the balance between shrinkage,printing efficiency,and fiexural strength.展开更多
Four types of resins,P1–P4,are used as binders for FeSiBC amorphous powder,which are then press-molded and heat-treated to fabricate magnetic powder cores(MPCs).By testing the permeability,loss,density,and radial cru...Four types of resins,P1–P4,are used as binders for FeSiBC amorphous powder,which are then press-molded and heat-treated to fabricate magnetic powder cores(MPCs).By testing the permeability,loss,density,and radial crush strength of MPCs,the effect of the binder on the magnetic properties of the cores is investigated and the best resin is found.The results show that the silicone resin P3 exhibits the best thermal stability,retaining 82.1%of its mass after heat treatment at 430°C.This contributes to improving the insulation of MPCs and reducing the eddy current loss,which is 46.06 mW cm^(−3)(150 kHz,20 mT)with the mechanical strength of 11.13 MPa.The bonding of epoxy resin P4 is superior to that of other resins,which significantly improves the powder compactness and makes MPCs density reach 5.67 g cm^(−3),and its permeability is as high as 28.7.The two types of resins have different advantages,and both lead to MPCs with excellent properties.展开更多
As a reliable additive manufacturing technology,the stereolithography(SLA)ceramic core necessitates a tailored sintering process to achieve optimal performance.This study explored the effects of final sintering temper...As a reliable additive manufacturing technology,the stereolithography(SLA)ceramic core necessitates a tailored sintering process to achieve optimal performance.This study explored the effects of final sintering temperatures(specifically 1,150,1,250,and 1,300°C)on the properties of SLA-fabricated SiO_(2)-based ceramic cores reinforced with nano-ZrO_(2)(at concentrations of 1.0wt.%,1.5wt.%,and 2.0wt.%).The results demonstrate that increasing the final sintering temperature and the incorporation of nano-ZrO_(2)enhance the viscous fiow of quartz glass,resulting in a higher sintering degree.As the final sintering temperature rises,the ceramic samples exhibit increased shrinkage rate,decreased apparent porosity,and increased bulk density.Higher final sintering temperatures also promote greater cristobalite precipitation,promoting an increase in the amount and precipitation rate of quartz during investment casting.The formation of a cristobalite and ZrSiO_4 network at elevated temperatures effectively inhibits the viscous flow of quartz glass,thereby significantly improving high-temperature flexural strength and creep resistance of ceramic cores.When the content of nano-ZrO_(2)is between 1.5wt.%and 2.0wt.%,the final sintering temperature of 1,250°C is the best choice.Under these conditions,the shrinkage rate along the Z direction ranges from 3.35%to 3.68%,the porosity lies between 25.57%and 26.03%,the bulk density varies from 1.612 to 1.645 g·cm^(-3),the room temperature fiexural strength is between 26.79 and 27.85 MPa,and the fiexural strength at high temperatures is within the range of 30.77 to 33.02 MPa.The defiection at high-temperatures is 3.37-5.31 mm,while the surface roughness of the upper surface is 3.26-4.79μm,and the surface roughness of the side surface is 4.97-5.79μm.These findings provide valuable guidance for optimizing the sintering processes of SLA ceramic cores,offering potential for industrial applications.展开更多
In this paper, we obtained three dimensional digital cores using X-ray CT to describe the rock microstructure and applied the open morphology algorithm to simulate oil and formation water distribution in the pore spac...In this paper, we obtained three dimensional digital cores using X-ray CT to describe the rock microstructure and applied the open morphology algorithm to simulate oil and formation water distribution in the pore space at different water saturations during the oil-displacing water flood process. The resistivity, formation factor, and resistivity index of rocks were calculated using the finite element method （FEM） and we studied the effect of rock wettability on electrical properties. The numerical simulation results indicate that the simulated formation factor and resistivity index of the water wet rock agrees well with experiments over the whole range of water saturation and extends the traditional resistivity experiment. The rock wettablilty has a large influence on the rock resistivity index. The resistivity and saturation exponent of oil wet rock are obviously larger than three of water wet rock.展开更多
In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize ph...In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize phase transformations in the samples, and the XRD result indicated that the addition of alumina pro- moted crystallization of fused silica during sintering at 1180-1220 ℃ and thus increases the amount of cristobalite. The increased amount of cristobalite as well as alumina addition led to much more thermal dilation due to their higher coefficients of thermal expansion than that of fused silica. The flexural strengths at room temperature and 1500 ~C were tested, and it was shown that alumina addition could not affect room temperature strength, but decreased the flexural strength at 1500 ℃. In addition, deflection resis- tance during heating to high temperatures was investigated, and the result indicated that alumina addition speeded up high temperature softening of the samples. XRD and scanning electron microscopy equipped with energy dispersive spectrometry （SEMJEDS） analysis suggested that this softening behavior was related with viscous flow sintering which could be accelerated by the reaction of alumina and silica with a product of mullite.展开更多
High porosity and high strength are usually mutually exclusive in the preparation of ceramic materials.However,high porosity and flexural strength are required for the preparation of complex ceramic cores for hollow t...High porosity and high strength are usually mutually exclusive in the preparation of ceramic materials.However,high porosity and flexural strength are required for the preparation of complex ceramic cores for hollow turbine blades.In this study,Al_(2)O_(3)cores with high porosity and high flexural strength were successfully prepared using digital light processing(DLP)3 D printing technology.The influence of sintering temperature on the microstructure,pore evolution,and flexural strength of the cores were investigated.With an increase in the sintering temperature,the porosity of the ceramic cores first increased and then decreased,reaching a maximum value of 35%at 1400℃.The flexural strength increased with the increase in sintering temperature,but at 1400℃the incremental enhancement of flexural strength was greatest.Combined with the core service requirements and core performance,this study selected 1400℃(open porosity of 35.1%and flexural strength of 20.3 MPa)as the optimal sintering temperature for the DLP-3 D printed Al_(2)O_(3)core.展开更多
Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in formi...Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in forming complex ceramic cores,but how to balance the porosity and strength is an enormous challenge.In this work,alumina ceramic cores with high porosity,moderate strength,and low high-temperature deflection were prepared using stereolithography(SLA)3D printing by a novel powder gradation design strategy.The contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse,medium,and fine particles is 2:1:1 and the sintering temperature is 1600℃.The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder system.The sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain size.On this basis,a"non-skeleton"microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and properties.As a result,high porosity(36.4%),appropriate strength(50.1 MPa),and low high-temperature deflection(2.27 mm)were achieved by optimizing particle size gradation and sintering process,which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.展开更多
基金financially supported by the National Key R&D Program of China(No.2023YFB4606101)the National Key R&D Program of China(No.2022YFB4601404)+3 种基金the Innovative and Entrepreneurial PhD Program of Jiangsu Province(No.JSSCBS20210836)the youth program of Jiangnan University(No.JUSRP121038)the Taihu Talent Program of Wuxi Citythe Innovative and Entrepreneurial Talent Program of Jiangsu Province(No.JSSCRC2021531)。
文摘Alumina ceramics are crucial for high-performance applications,such as turbine blades,due to their excellent thermal stability and mechanical properties.However,existing fabrication methods often fail to balance strength,porosity,and dimensional precision.This study partially fills this research gap through a systematic investigation of calcium oxide(CaO)doping effects on alumina ceramic cores fabricated via ceramic stereolithography,with controlled doping ratios and sintering parameters.A ceramic paste was prepared using coarse and fine Al_(2)O_(3) particles mixed with CaO as a sintering aid,followed by debinding and sintering to achieve optimal mechanical properties.The results show that CaO doping significantly enhances the fiexural strength of alumina cores while maintaining porosity levels between 20%and 30%and controlling the sintering shrinkage rate to about 5%.Additionally,CaO doping alters the microstructure by inhibiting the transformation of spherical fine particles into fiaky grains,improving sintering activity.However,as the CaO doping content increases,the bending strength increases,while the shrinkage rate of the material also tends to increase,resulting in a reduction in the overall porosity.This has a negative impact on the control of the manufacturing precision of turbine blades.Thus,although CaO doping improves strength and microstructure,achieving necessary dimensional control requires further optimization of doping content and sintering conditions.
基金financially supported by the National Natural Science Foundation of China(Nos.52402094,U234120139,and U22A20129)the National Defense Basic Scientific Research Program of China(No.JCKY2022130C005)+8 种基金the China Postdoctoral Science Foundation(No.2023M743571)the Postdoctoral Fellowship Program of CPSF(N o.GZC20232743)the Innovation Project of IMR(2024-PY11)the Open Research Fund of National Key Laboratory of Advanced Casting Technologies(No.CAT2023-006)the Graduate Education Quality Engineering Project of Anhui Province(No.2023cxcysj015)the Science and Technology Plan Project of Liaoning Province(No.2024JH2/101900011)the Nationa Key Research and Development Program of China(Nos2024YFB3714500 and 2018YFB1106600)the China United Gas Turbine Technology Co.Ltd.under the project of J790。
文摘Ceramic cores are important in the fabrication of superalloy hollow blades,which are increasingly characterized by intricate internal cavity channels.This complexity poses significant challenges to traditional manufacturing processes.The vat photopolymerization 3D printing technology provides a new choice for ceramic cores with complex structures.However,the lamellar structure of the vat photopolymerization 3D printed ceramic cores leads to the anisotropy.Meanwhile,the low strength and high shrinkage of ceramic cores restrict their industrial application.In this study,using Al_(2)O_(3)powder as the main material,the effects of zircon content on the sintering shrinkage,open porosity,fiexural strength,and other properties of Al_(2)O_(3)-based ceramic cores were studied to address the aforementioned issues.The influencing mechanism of zircon distribution on sintering shrinkage was analyzed,and the strengthening mechanism of mullite on ceramic cores was discussed from both thermodynamics and dynamics aspects.Through the comprehensive evaluation of ceramic core properties,the Al_(2)O_(3)-based ceramic core with 15vol.%zircon exhibites the optimal performance.Compared with the core samples without zirconium addition,the fiexural strength of the Al_(2)O_(3)-based ceramic core with 15vol.%zircon increases from 14.80 MPa to 61.54 MPa at 25°C,an increase of 315.8%;and from 4.91 MPa to 11.59 MPa at 1,500°C,an increase of 136.0%.The shrinkage in the Z-axis is reduced by 21%,which better weakens the anisotropy of the shrinkage of 3D printed Al_(2)O_(3)-based ceramic cores.ZrO_(2)phase and mullite phase are formed by zircon,which improve the comprehensive properties of Al_(2)O_(3)-based ceramic cores.The successful 3D printing of high-performance Al_(2)O_(3)-based ceramic cores via vat photopolymerization has promoted its industrial application for fabricating ceramic cores with complex structures.
基金provided by the National Defense Basic Scientific Research Program (Grant No.JCKY2022213C008)。
文摘Ceramic cores are key components in the production of castings with complex cavity structures. With the continuous development of the aerospace field, the demand for the castings with complex cavity structures is increasing. When using insoluble ceramic cores for casting, there is a significant challenge in removing complex blind cavities, which severely affects the completeness of the shape of the castings. Soluble ceramic cores can disintegrate when placed in water, greatly simplifying the removal process of cores and ensuring the complete formation of castings with complex cavity structures. Additive manufacturing technology, compared to traditional methods for preparing the soluble ceramic cores, does not require molds and can achieve direct forming of complex cores, simplifying the preparation process and reducing production time and costs. Nowadays, various additive manufacturing technologies, such as stereolithography(SL), selective laser sintering(SLS), direct ink writing(DIW), and binder jetting(BJ) technologies, have been successfully applied to the preparation of the ceramic cores. This paper analyzed the advantages and limitations of various additive manufacturing technologies, reviewed the research progress and raw material classifications of soluble ceramic cores prepared by these technologies, and looked forward to the future developments in the preparation of soluble ceramic cores using additive manufacturing technologies.
基金supported by the National Natural Science Foundation of China (Grant No. 52275310)。
文摘The complex ceramic core used for hollow turbine blades requires a high porosity and a high fiexural strength. For a better balance between porosity and fiexural strength, ceramic materials with porous structures are preferred. In order to achieve the transition from disordered pore formation to ordered pore formation, Al_(2)O_(3) ceramic cores with triply periodic minimal surface(TPMS) micro lattice structures with different structural configurations(gyroid, diamond, and neovius) and different volume fractions of lattice structures(30, 40, and 50, vol.%) were designed and prepared by vat photopolymerization 3D printing. The effects of structural configuration and volume fraction of the lattice structure on the following structural shrinkage, microstructure, and flexural strength were investigated. The shrinkage relationship of the three lattice configurations is: neovius>diamond>gyroid. Besides, it is found that with an increase in the volume fraction of the 3D printed Al_(2)O_(3) ceramic micro lattice structures, their fiexural strength correspondingly increases ranging from 54.95 MPa to 139.1 MPa. The maximum average fiexural strength of the 3D printed Al_(2)O_(3) ceramic micro lattice structures is obtained when the structural configuration is diamond and with a volume fraction of 50vol.%, which is 139.1 MPa. Even when the volume fraction of the lattice structure is 30vol.%, that is to say the porosity is 70%, the fiexural strength is as high as 50-70 MPa, which can still be maintained at a high level. In addition, when the volume fraction of the lattice structure is a certain value, the sample with diamond configuration has a higher strength. The internal pore morphology, pore size, and porosity of the cores are precisely controlled, achieving both a high porosity and a high strength. Therefore, this study maintains high porosity and high strength simultaneously, providing a new lattice structure design idea for 3D printed ceramic cores.
基金financially supported by the Liaoning Province Science and Technology Plan Joint Program(2023JH2/101700037).
文摘Ceramic cores are key to forming a cooling structure within the hollow blade cavities.The use of stereolithography(SL)3D printing technology eliminates the need for moulds,facilitating the preparation of complex-shaped ceramic cores.In this study,silica-based ceramic cores incorporating nano-3YSZ(3mol.% yttria stabilised zirconia)and micron-sized Y_(2)O_(3) were prepared via SL 3D printing ceramic technology to promote the formation of cristobalite and ZrSiO_(4),thereby improving the high-temperature properties.The flexural strength at 25℃ and 1,500℃,deflection at 1,500℃,shrinkage rate,and porosity of the core samples sintered at different temperatures(1,170℃,1,185℃,1,200℃,1,215℃,and 1,230℃)were tested and investigated.The mechanism underlying the high temperature performance of the cores was elucidated through analysis of cross-sectional morphology,element distribution,and phase constitution of the samples.As the sintering temperature increases,the shrinkage and flexural strength at 25℃ of the core rise,while the open porosity and deflection at 1,500℃ decrease.When the sintering temperature reaches 1,200℃ or higher,the 1,500℃ flexural strength can be measured,which increases as the sintering temperature rises.The core exhibits excellent creep resistance when sintered at temperatures of 1,200℃ and above.Considering the comprehensive performance requirements for the core,the sintering temperature of 1,200℃ was selected.At the sintering temperature of 1,200℃,the core exhibits shrinkage rates of 3.76%(X),3.38%(Y),and 3.95%(Z),alongside a flexural strength of 9.01 MPa at 25℃ and 32.15 MPa at 1,500℃,and an open porosity of 26.39%.The deflection of the core at 1,500℃ is 0.15 mm,which helps to maintain the dimensional stability of the ceramic core during casting.XRD results indicate that samples fractured after 25℃ flexural strength test still contain amorphous quartz glass,alongside substantial quantities of yttria stabilized zirconia and Y_(2)O_(3).Samples fractured after 1,500℃ flexural strength test exhibit significant crystallisation of amorphous quartz glass into cristobalite,with silica and 3YSZ combining to form ZrSiO_(4).Y_(2)O_(3) as a network modifier of the glass network destroys the bridging oxygen in the silica-oxygen bond,thereby reducing the energy required for glass crystallisation and promoting the crystallisation reaction of quartz glass to form cristobalite.In addition,nano-3YSZ combines with SiO_(2) at high temperatures to form ZrSiO_(4).Since cristobalite and ZrSiO_(4) are crystals,both of them have strong creep resistance,thus improving the high temperature flexural strength and deformation resistance of the ceramic cores.
基金supported by the National Key R&D Program of China(Grant Nos.2024YFB3714502,2024YFB3714501,2024YFB3714504)the National Natural Science Foundation of China(Grant Nos.52130204,52174376)+5 种基金the TQ Innovation Foundation(Grant No.23-TQ09-02-ZT-01-005)the Aeronautical Science Foundation of China(Grant No.20220042053001)the Ningbo Science and Technology Plan Project(Grant No.2025Z070)the Key R&D Project of Shaanxi Province(Grant Nos2024GX-YBXM-220,2024CY-GJHX-29,2024GX-ZDCYL-03-03,2024GX-YBXM-400)the National Advanced Rare Metal Materials Innovation Center Project[Grant No.2024 ZG-GCZX-01(1)-01]the Foundation of China Scholarship Council(Grant No.202406290136)。
文摘To meet the evolving demands of aeroengine development,the structural and performance requirements for ceramic cores have become increasingly stringent.Vat photopolymerization 3D printing,owing to its moldless,fiexible manufacturing,and other advantages,demonstrates significant potential in the preparation of ceramic cores with intricate structures.However,its practical application still faces multiple challenges,including layered structures and property anisotropy,defects such as cracks and collapse during printing and sintering,forming inaccuracies,and difficulties in controlling surface roughness.Recent advances have focused on optimizing slurry formulation and rheology,improving curing behavior,introducing auxiliary powders and additives,tailoring forming parameters,and optimizing the sintering process.Nevertheless,effectively suppressing lamellar defects,achieving superior dimensional accuracy,and maintaining high surface quality in complex structures remain the core scientific and technical issues to be solved.Future research should concentrate on refining curing mechanisms,advancing powder design and organic system optimization,and regulating the coupled processes of forming,debinding,and sintering to accelerate the application of VPP 3D printed ceramic cores in aerospace manufacturing.
基金supported by the Doctoral Research Initiation Fund Project of Hebei Normal University(No.L2025B19)PhD Fellowship of the State Key Laboratory of Marine Environmental Science at Xiamen University.
文摘Protoporphyrin Ⅸ(PPⅨ), a basic porphyrin system found in nature, all “porphyrin-type”tetrapyrroles with a biological function are biosynthetically derived thereof. PPⅨ is a metalloprosthetic group of numerous proteins involved in diverse metabolic and respiratory processes across all domains of life, and is thus considered essential for respiring organisms. Determining the biotic and abiotic factors that influence marine microbial growth and community structure is critical for understanding global biogeochemical cycles. Here,we present vertical profiles of intracellular PPⅨ and four derivative products(Chlorophylla/b and Pheophytin-a/b) from two coastal sediment cores, alongside ancillary geochemical and 16S rRNA microbial community data. Our findings indicated that PPⅨ is present in the natural sediment environment and displays a decreasing trend with depth, revealing a significant positive correlation with both organic matter and microbial abundance. Cooccurrence networks revealed that the environmental distribution of PPⅨ was positively correlated with the microbial porphyrin producer(high genetic completeness), but negatively correlated with auxotrophs(absence or low genetic completeness). It emphasized the critical role of PPⅨ as a biological molecule involved in key physiological processes. These results suggest that PPⅨ is a prominent component of the shared extracellular metabolite pool, especially in anoxic marine sediments where it exists at physiologically relevant concentrations for microbial metabolism. This study highlighted the significance of PPⅨ in microbial ecology and its potential impact on biogeochemical cycles in marine sedimentary environments.
文摘Aimed at the long and narrow geometric features and poor generalization ability of the damage detection in conveyor belts with steel rope cores using the X-ray image,a detection method of damage X-ray image is proposed based on the improved fully convolutional one-stage object detection(FCOS)algorithm.The regression performance of bounding boxes was optimized by introducing the complete intersection over union loss function into the improved algorithm.The feature fusion network structure is modified by adding adaptive fusion paths to the feature fusion network structure,which makes full use of the features of accurate localization and semantics of multi-scale feature fusion networks.Finally,the network structure was trained and validated by using the X-ray image dataset of damages in conveyor belts with steel rope cores provided by a flaw detection equipment manufacturer.In addition,the data enhancement methods such as rotating,mirroring,and scaling,were employed to enrich the image dataset so that the model is adequately trained.Experimental results showed that the improved FCOS algorithm promoted the precision rate and the recall rate by 20.9%and 14.8%respectively,compared with the original algorithm.Meanwhile,compared with Fast R-CNN,Faster R-CNN,SSD,and YOLOv3,the improved FCOS algorithm has obvious advantages;detection precision rate and recall rate of the modified network reached 95.8%and 97.0%respectively.Furthermore,it demonstrated a higher detection accuracy without affecting the speed.The results of this work have some reference significance for the automatic identification and detection of steel core conveyor belt damage.
文摘For the first time,the linear and nonlinear vibrations of composite rectangular sandwich plates with various geometric patterns of lattice core have been analytically examined in this work.The plate comprises a lattice core located in the middle and several homogeneous orthotropic layers that are symmetrical relative to it.For this purpose,the partial differential equations of motion have been derived based on the first-order shear deformation theory,employing Hamilton’s principle and Von Kármán’s nonlinear displacement-strain relations.Then,the nonlinear partial differential equations of the plate are converted into a time-dependent nonlinear ordinary differential equation(Duffing equation)by applying the Galerkin method.From the solution of this equation,the natural frequencies are extracted.Then,to calculate the non-linear frequencies of the plate,the non-linear equation of the plate has been solved analytically using the method of multiple scales.Finally,the effect of some critical parameters of the system,such as the thickness,height,and different angles of the stiffeners on the linear and nonlinear frequencies,has been analyzed in detail.To confirmthe solution method,the results of this research have been compared with the reported results in the literature and finite elements in ABAQUS,and a perfect match is observed.The results reveal that the geometry and configuration of core ribs strongly affect the natural frequencies of the plate.
基金supported by the Chinese Academy of Sciences Strategic Leading Science and Technology projects(Grant No.XDB10010400)the China Postdoctoral Science Foundation(Grant No.2015M570142)
文摘The dependence of elastic moduli of shales on the mineralogy and microstructure of shales is important for the prediction of sweet spots and shale gas production. Based on 3D digital images of the microstructure of Longmaxi black shale samples using X-ray CT, we built detailed 3D digital images of cores with porosity properties and mineral contents. Next, we used finite-element （FE） methods to derive the elastic properties of the samples. The FE method can accurately model the shale mineralogy. Particular attention is paid to the derived elastic properties and their dependence on porosity and kerogen. The elastic moduli generally decrease with increasing porosity and kerogen, and there is a critical porosity （0.75） and kerogen content （ca. ≤3%） over which the elastic moduli decrease rapidly and slowly, respectively. The derived elastic moduli of gas- and oil-saturated digital cores differ little probably because of the low porosity （4.5%） of the Longmaxi black shale. Clearly, the numerical experiments demonstrated the feasibility of combining microstructure images of shale samples with elastic moduli calculations to predict shale properties.
基金The National Natural Science Foundation of China(No.60773216)the National High Technology Research and Development Program of China(863Program)(No.2006AA010109)+1 种基金the Natural Science Foundation of Renmin University of China(No.06XNB052)Free Exploration Project(985 Project of Renmin University of China)(No.21361231)
文摘This paper focuses on some key problems in web community discovery and link analysis.Based on the topic-oriented technology,the characteristics of a bipartite graph are studied.An Х bipartite core set is introduced to more clearly define extracting ways.By scanning the topic subgraph to construct Х bipartite graph and then prune the graph with i and j ,an Х bipartite core set,which is also the minimum element of a community,can be found.Finally,a hierarchical clustering algorithm is applied to many Х bipartite core sets and the dendrogram of the community inner construction is obtained.The correctness of the constructing and pruning method is proved and the algorithm is designed.The typical datasets in the experiment are prepared according to the way in HITS（hyperlink-induced topic search）.Ten topics and four search engines are chosen and the returned results are integrated.The modularity,which is a measure of the strength of the community structure in the social network,is used to validate the efficiency of the proposed method.The experimental results show that the proposed algorithm is effective and efficient.
基金financially supported by the National Natural Science Foundation of China(No.52102062)the Xi’an Science and Technology Plan Project(No.23LLRH0004)the Key Research and Development Project of Shaanxi Province of China(2024GX-YBXM-352)。
文摘Vat photopolymerization(VPP)3D printing is an optimized technology for complex-shaped ceramic cores,in which the solid loading of ceramic slurries greatly infiuences the microstructure and property of the final ceramic parts.However,the high solid loading of slurries is highly limited by the high viscosity.In this study,silica-based ceramic core slurries with solid loading up to 68vol.%were achieved by the composition design to optimize the performance,considering the curing,rheological,and double bond conversion rate.The slurries demonstrate superior curing and rheological performance with mass ratio of monomers being 3:2 and mass fraction of BYK111 being 4wt.%.Afterwards,the impact of solid loading on the morphology and mechanical properties was investigated.As the solid loading increases,the microstructure becomes gradually dense,leading to an improved flexural strength of 19.5 MPa.Additionally,the sintering shrinkage becomes more uniform,satisfying the casting requirements effectively.This work serves as a guide for the preparation of ceramic slurries with a high solid loading.
基金the Youth Innovation Promotion Association of Chinese Academy of Science(No.2021160)the National Natural Science Foundation of China(No.51802319)the Technology and Engineering Center for Space(No.CSU-QZKT-2019-04)。
文摘Ceramic cores fabricated by stereolithography exhibit great potential in casting turbine blades.Previous research on ceramic core molding was primarily conducted using vertical printing techniques,which not only resulted in lengthy molding durations but also compromised the mechanical strength.In this work,silica(SiO--_2)ceramic cores,with fine complex geometric shapes,were fabricated using 65vol.%ceramic slurry by digital light processing(DLP)with different printing angles.Printing angles significantly impact the surface accuracy,shrinkage,printing efficiency of green bodies,as well as the microstructure and mechanical properties of sintered ceramic core samples.As the printing angle in the green body increases,the bonding area decreases,surface roughness on the XY plane worsens,shrinkage in the Z direction becomes more pronounced,and the printing efficiency declines.Similarly,an increase in the printing angle in the sintered body leads to a reduction in bending strength.At a printing angle of 30°,the printing time is reduced to half of that at 90°,which improves the molding efficiency.Meanwhile,the obtained bulk density of 1.71 g·cm~(-3),open porosity of 24%,and fiexural strength of 10.6±1 MPa can meet the requirements of sintered ceramic cores.Therefore,designing and optimizing the printing angles can achieve the balance between shrinkage,printing efficiency,and fiexural strength.
基金financially supported by the Key research and development project of Shandong province in China(Grant No.2022CXGC020308).
文摘Four types of resins,P1–P4,are used as binders for FeSiBC amorphous powder,which are then press-molded and heat-treated to fabricate magnetic powder cores(MPCs).By testing the permeability,loss,density,and radial crush strength of MPCs,the effect of the binder on the magnetic properties of the cores is investigated and the best resin is found.The results show that the silicone resin P3 exhibits the best thermal stability,retaining 82.1%of its mass after heat treatment at 430°C.This contributes to improving the insulation of MPCs and reducing the eddy current loss,which is 46.06 mW cm^(−3)(150 kHz,20 mT)with the mechanical strength of 11.13 MPa.The bonding of epoxy resin P4 is superior to that of other resins,which significantly improves the powder compactness and makes MPCs density reach 5.67 g cm^(−3),and its permeability is as high as 28.7.The two types of resins have different advantages,and both lead to MPCs with excellent properties.
基金supported by the Natural Science Foundation of Shanghai(No.23ZR1421500)the National Natural Science Foundation of China(Nos.52474412,52127807,52271035)+3 种基金the Shanghai Municipal Commission of Economy and Informatization(No.GYOJ2022-2-02)the United Innovation Program of Shanghai Commercial Aircraft Engine(No.AR966)the SPMI Project from Shanghai Academy of Spaceflight Technology(No.SPMI2022-06)the Ningbo International Science and Technology Cooperation Program(No.2023H004)。
文摘As a reliable additive manufacturing technology,the stereolithography(SLA)ceramic core necessitates a tailored sintering process to achieve optimal performance.This study explored the effects of final sintering temperatures(specifically 1,150,1,250,and 1,300°C)on the properties of SLA-fabricated SiO_(2)-based ceramic cores reinforced with nano-ZrO_(2)(at concentrations of 1.0wt.%,1.5wt.%,and 2.0wt.%).The results demonstrate that increasing the final sintering temperature and the incorporation of nano-ZrO_(2)enhance the viscous fiow of quartz glass,resulting in a higher sintering degree.As the final sintering temperature rises,the ceramic samples exhibit increased shrinkage rate,decreased apparent porosity,and increased bulk density.Higher final sintering temperatures also promote greater cristobalite precipitation,promoting an increase in the amount and precipitation rate of quartz during investment casting.The formation of a cristobalite and ZrSiO_4 network at elevated temperatures effectively inhibits the viscous flow of quartz glass,thereby significantly improving high-temperature flexural strength and creep resistance of ceramic cores.When the content of nano-ZrO_(2)is between 1.5wt.%and 2.0wt.%,the final sintering temperature of 1,250°C is the best choice.Under these conditions,the shrinkage rate along the Z direction ranges from 3.35%to 3.68%,the porosity lies between 25.57%and 26.03%,the bulk density varies from 1.612 to 1.645 g·cm^(-3),the room temperature fiexural strength is between 26.79 and 27.85 MPa,and the fiexural strength at high temperatures is within the range of 30.77 to 33.02 MPa.The defiection at high-temperatures is 3.37-5.31 mm,while the surface roughness of the upper surface is 3.26-4.79μm,and the surface roughness of the side surface is 4.97-5.79μm.These findings provide valuable guidance for optimizing the sintering processes of SLA ceramic cores,offering potential for industrial applications.
基金sponsored by NSFC(Grant No.40574030)CNPC research project(Grant No.06A30102)
文摘In this paper, we obtained three dimensional digital cores using X-ray CT to describe the rock microstructure and applied the open morphology algorithm to simulate oil and formation water distribution in the pore space at different water saturations during the oil-displacing water flood process. The resistivity, formation factor, and resistivity index of rocks were calculated using the finite element method （FEM） and we studied the effect of rock wettability on electrical properties. The numerical simulation results indicate that the simulated formation factor and resistivity index of the water wet rock agrees well with experiments over the whole range of water saturation and extends the traditional resistivity experiment. The rock wettablilty has a large influence on the rock resistivity index. The resistivity and saturation exponent of oil wet rock are obviously larger than three of water wet rock.
文摘In this work, the influences of alumina addition on cristobalite crystallization and properties of injec- tion molded silica-based ceramic cores were investigated. X-ray diffraction （XRD） was used to characterize phase transformations in the samples, and the XRD result indicated that the addition of alumina pro- moted crystallization of fused silica during sintering at 1180-1220 ℃ and thus increases the amount of cristobalite. The increased amount of cristobalite as well as alumina addition led to much more thermal dilation due to their higher coefficients of thermal expansion than that of fused silica. The flexural strengths at room temperature and 1500 ~C were tested, and it was shown that alumina addition could not affect room temperature strength, but decreased the flexural strength at 1500 ℃. In addition, deflection resis- tance during heating to high temperatures was investigated, and the result indicated that alumina addition speeded up high temperature softening of the samples. XRD and scanning electron microscopy equipped with energy dispersive spectrometry （SEMJEDS） analysis suggested that this softening behavior was related with viscous flow sintering which could be accelerated by the reaction of alumina and silica with a product of mullite.
基金financially supported by the Funding from the National Key R&D Program of China(No.2018YFB1106600)the Fundamental Research Funds for Central Universities(WK5290000002)。
文摘High porosity and high strength are usually mutually exclusive in the preparation of ceramic materials.However,high porosity and flexural strength are required for the preparation of complex ceramic cores for hollow turbine blades.In this study,Al_(2)O_(3)cores with high porosity and high flexural strength were successfully prepared using digital light processing(DLP)3 D printing technology.The influence of sintering temperature on the microstructure,pore evolution,and flexural strength of the cores were investigated.With an increase in the sintering temperature,the porosity of the ceramic cores first increased and then decreased,reaching a maximum value of 35%at 1400℃.The flexural strength increased with the increase in sintering temperature,but at 1400℃the incremental enhancement of flexural strength was greatest.Combined with the core service requirements and core performance,this study selected 1400℃(open porosity of 35.1%and flexural strength of 20.3 MPa)as the optimal sintering temperature for the DLP-3 D printed Al_(2)O_(3)core.
基金financially supported by the National Natural Science Foundation of China(Nos.52130204,52174376,51822405)Guangdong Basic and Applied Basic Research Foundation(No.21201910250000848)+5 种基金Science and Technology Innovation Team Plan of Shaan Xi Province(No.2021TD-17)The Youth Innovation Team of Shaanxi UniversitiesJoint Research Funds of the Department of Science&Technology of Shaanxi Province and NPU(2020GXLH-Z-024)Key R&D Program of Shaan Xi Province(No.2019ZDLGY 04-04)Fundamental Research Funds for the Central Universities(No.D5000210902)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(Nos.CX2021056 and CX2021066),China。
文摘Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in forming complex ceramic cores,but how to balance the porosity and strength is an enormous challenge.In this work,alumina ceramic cores with high porosity,moderate strength,and low high-temperature deflection were prepared using stereolithography(SLA)3D printing by a novel powder gradation design strategy.The contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse,medium,and fine particles is 2:1:1 and the sintering temperature is 1600℃.The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder system.The sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain size.On this basis,a"non-skeleton"microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and properties.As a result,high porosity(36.4%),appropriate strength(50.1 MPa),and low high-temperature deflection(2.27 mm)were achieved by optimizing particle size gradation and sintering process,which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.
