In this study,a kind of Ni-based superalloy specially designed for additive manufacturing(AM)was investigated.Thermo-Calc simulation and differential scanning calorimetry(DSC)analysis were used to determine phases and...In this study,a kind of Ni-based superalloy specially designed for additive manufacturing(AM)was investigated.Thermo-Calc simulation and differential scanning calorimetry(DSC)analysis were used to determine phases and their transformation temperature.Experimental specimens were prepared by laser metal deposition(LMD)and traditional casting method.Microstructure,phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy(SEM),transmission scanning electron microscopy(TEM),X-ray diffraction(XRD)and tensile tests.The results show that this alloy contains two basic phases,γ/γ’,in addition to these phases,at least two secondary phases may be present,such as MC carbides and Laves phases.Furthermore,the as-deposited alloy has finer dendrite,its mean primary dendrite arm space(PDAS)is about 30-45μm,and the average size ofγ’particles is 100-150 nm.However,the dendrite size of the as-cast alloy is much larger and its PDAS is 300-500μm with secondary and even third dendrite arms.Correspondingly,the alloy displays different tensile behavior with different processing methods,and the as-deposited specimen shows better ultimate tensile stress(1,085.7±51.7 MPa),yield stress(697±19.5 MPa)and elongation(25.8%±2.2%)than that of the as-cast specimen.The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites,γ’,and Laves phase,and the segregation of elements,etc.Such important information would be helpful for alloy application as well as new alloy development.展开更多
Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃...Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃.High-throughput specimens were fabricated to withstand different stresses at the same time.Isothermal oxidation s amples were analyzed using the mass gain method to obtain oxidation kinetic curves.The results show that the external stress below 200 MPa could improve the oxidation resistance of the GH4738.With tensile stress increasing,the oxide layer becomes thinner,denser and more complete,while internal oxidation decreases.The tensile stress alters the structure of the external oxide layer from a two-layer to a threelayer configuration.The Cr_(2)O_(3) oxide layer inhibits the outward diffusion of Ti,leading to Ti enrichment at the oxide-matrix interface and altering the oxidation mechanism of GH4738.展开更多
Two experimental alloys containing diff erent contents of Ru were investigated to study the eff ect of Ru on the microstructural evolution during long-term thermal exposure.The increase in Ru promoted the formation of...Two experimental alloys containing diff erent contents of Ru were investigated to study the eff ect of Ru on the microstructural evolution during long-term thermal exposure.The increase in Ru promoted the formation of cubical,tiny,and evenγ′phase after full heat treatment.Moreover,the samples after full heat treatment were exposed at 1100℃ for diff erent time.Based on the classical model by Lifshitz,Slyozov,and Wagner,the coarsening ofγ′phase of the alloy containing 2.5 and3.5 wt.%Ru during the long-term aging was controlled by the interface reaction and diff usion,respectively.Theγ/γ′lattice misfi t was more negative with the increment of Ru addition,which induced the formation of stable raftedγ′phase in the alloy containing 3.5 wt.%Ru at the initiation of long-term aging.Besides,the increase in Ru reduced the diff usion coeffi cient,which could restrain theγ′phase coarsening.The lowerγ/γ′lattice misfi t of the alloy containing 2.5 wt.%Ru promoted the interface reaction,which induced the rapid coarsening ofγ′phase.Therefore,the increase in Ru improved the microstructural stability of the alloys.On the other hand,the raise of Ru induced"reverse partitioning"behavior,which was eff ective in suppressing the emergence of the topologically close-packed phase(TCP phase).The TCP phase occasionally occurred in the alloy containing 2.5 wt.%Ru,which was attributed to the high temperature and the supersaturation of theγmatrix.Moreover,the TCP phase was determined asμphase,which had a high concentration of Co,Re,Mo,and W.A sketch map describing the evolution of the TCP phase was also constructed.展开更多
Mutually interacting components form complex systems and these components usually have long- range cross-correlated outputs. Using wavelet leaders, we propose a method for characterizing the joint multifractal nature ...Mutually interacting components form complex systems and these components usually have long- range cross-correlated outputs. Using wavelet leaders, we propose a method for characterizing the joint multifractal nature of these long-range cross correlations; we call this method joint multifractal analysis based on wavelet leaders （MF-X-WL）. We test the validity of tile MF-X-WL method by performing extensive numerical experiments on dual binomial measures with multifractal cross correlations and bivariate fractional Brownian motions （bFBMs） with monofractal cross correlations. Both experiments indicate that MF-X-WL is capable of detecting cross correlations in synthetic data with acceptable estimating errors. We also apply the MF-X-WL method to pairs of series from financial markets （returns and volatilities） and online worlds （online numbers of different genders and different societies） and determine intriguing joint multifractal behavior.展开更多
基金the financial supports from the National Science and Technology Major Project,China(No.Y2019-VII-0011-0151)the National Natural Science Foundation of China(No.51771190)。
基金financially supported by the National Science and Technology Major Project(Y2019-Ⅶ-0011-0151)the National Natural Science Foundation of China(No.51771190)。
文摘In this study,a kind of Ni-based superalloy specially designed for additive manufacturing(AM)was investigated.Thermo-Calc simulation and differential scanning calorimetry(DSC)analysis were used to determine phases and their transformation temperature.Experimental specimens were prepared by laser metal deposition(LMD)and traditional casting method.Microstructure,phase constitution and mechanical properties of the alloy were characterized by scanning electron microscopy(SEM),transmission scanning electron microscopy(TEM),X-ray diffraction(XRD)and tensile tests.The results show that this alloy contains two basic phases,γ/γ’,in addition to these phases,at least two secondary phases may be present,such as MC carbides and Laves phases.Furthermore,the as-deposited alloy has finer dendrite,its mean primary dendrite arm space(PDAS)is about 30-45μm,and the average size ofγ’particles is 100-150 nm.However,the dendrite size of the as-cast alloy is much larger and its PDAS is 300-500μm with secondary and even third dendrite arms.Correspondingly,the alloy displays different tensile behavior with different processing methods,and the as-deposited specimen shows better ultimate tensile stress(1,085.7±51.7 MPa),yield stress(697±19.5 MPa)and elongation(25.8%±2.2%)than that of the as-cast specimen.The differences in mechanical properties of the alloy are due to the different morphology and size of dendrites,γ’,and Laves phase,and the segregation of elements,etc.Such important information would be helpful for alloy application as well as new alloy development.
基金financially supported by the National Key R&D Program of China(No.2021YFB3700401)Shandong Provincial Natural Science Foundation for Youths(No.ZR2022QE234)+1 种基金Zhejiang Provincial Natural Science Foundation(No.LQ21E030002)the Youth Innovation team Project of Higher Education Institutions in Shandong Province(No.2022KJ272)。
文摘Revealing the oxidation behavior of superalloys is crucial for optimizing material properties and extending service life.This study investigated the oxidation behavior of superalloy GH4738 under stress states at 850℃.High-throughput specimens were fabricated to withstand different stresses at the same time.Isothermal oxidation s amples were analyzed using the mass gain method to obtain oxidation kinetic curves.The results show that the external stress below 200 MPa could improve the oxidation resistance of the GH4738.With tensile stress increasing,the oxide layer becomes thinner,denser and more complete,while internal oxidation decreases.The tensile stress alters the structure of the external oxide layer from a two-layer to a threelayer configuration.The Cr_(2)O_(3) oxide layer inhibits the outward diffusion of Ti,leading to Ti enrichment at the oxide-matrix interface and altering the oxidation mechanism of GH4738.
基金financially supported by the National Science and Technology Major Project(No.2017-VI-0002–0072)the National Key R&D Program of China(No.2017YFA0700704)+1 种基金the National Natural Science Foundation of China(Nos.51671188,51601192 and 51701210)the Youth Innovation Promotion Association,Chinese Academy of Sciences and State Key Lab of Advanced Metals and Materials Open Fund(No.2018-Z07)。
文摘Two experimental alloys containing diff erent contents of Ru were investigated to study the eff ect of Ru on the microstructural evolution during long-term thermal exposure.The increase in Ru promoted the formation of cubical,tiny,and evenγ′phase after full heat treatment.Moreover,the samples after full heat treatment were exposed at 1100℃ for diff erent time.Based on the classical model by Lifshitz,Slyozov,and Wagner,the coarsening ofγ′phase of the alloy containing 2.5 and3.5 wt.%Ru during the long-term aging was controlled by the interface reaction and diff usion,respectively.Theγ/γ′lattice misfi t was more negative with the increment of Ru addition,which induced the formation of stable raftedγ′phase in the alloy containing 3.5 wt.%Ru at the initiation of long-term aging.Besides,the increase in Ru reduced the diff usion coeffi cient,which could restrain theγ′phase coarsening.The lowerγ/γ′lattice misfi t of the alloy containing 2.5 wt.%Ru promoted the interface reaction,which induced the rapid coarsening ofγ′phase.Therefore,the increase in Ru improved the microstructural stability of the alloys.On the other hand,the raise of Ru induced"reverse partitioning"behavior,which was eff ective in suppressing the emergence of the topologically close-packed phase(TCP phase).The TCP phase occasionally occurred in the alloy containing 2.5 wt.%Ru,which was attributed to the high temperature and the supersaturation of theγmatrix.Moreover,the TCP phase was determined asμphase,which had a high concentration of Co,Re,Mo,and W.A sketch map describing the evolution of the TCP phase was also constructed.
基金We acknowledge financial support from the National Natural Science Foundation of China （11375064 and 71532009）, the Program for Changjiang Scholars and Innovative Research Team in University （IRT1028）, and the Fundamental Re- search Funds for the Central Universities.
文摘Mutually interacting components form complex systems and these components usually have long- range cross-correlated outputs. Using wavelet leaders, we propose a method for characterizing the joint multifractal nature of these long-range cross correlations; we call this method joint multifractal analysis based on wavelet leaders （MF-X-WL）. We test the validity of tile MF-X-WL method by performing extensive numerical experiments on dual binomial measures with multifractal cross correlations and bivariate fractional Brownian motions （bFBMs） with monofractal cross correlations. Both experiments indicate that MF-X-WL is capable of detecting cross correlations in synthetic data with acceptable estimating errors. We also apply the MF-X-WL method to pairs of series from financial markets （returns and volatilities） and online worlds （online numbers of different genders and different societies） and determine intriguing joint multifractal behavior.
