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Low cycle fatigue properties and microstructure evolution at 760℃ of a single crystal superalloy

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Progress in Natural Science:Materials International 2015年第1期25卷 78-83页

作者： Zhenxue Shi Xiaoguang Wang shizhong liu Jiarong Li Science and Technology on Advanced High Temperature Structural Materials Laboratory Beijing Institute of Aeronautical Materials

Low cycle fatigue(LCF) behavior of a single crystal superalloy was investigated at 760 ℃. Microstructure evolution and fracture mechanism were studied by scanning electron microscopy(SEM) and transmission electron microscopy(TEM), respectively. The results show that the fatigue data fluctuation was small and the fatigue parameters of the alloy had been determined. On increasing the cyclic number, the alloy initially showed slight cyclic softening at the early two or three cycles and slowly hardened to some extent afterwards, then kept stable for the most of the remaining fatigue life. The LCF of the alloy at 760 ℃ can be attributed to the main elastic damage in fatigue processing. The initiation site of fatigue crack was at or near the surface of the samples. Crack propagated perpendicularly to the loading direction at first and then along {111}octahedral slip planes. The fatigue fracture mechanism was quasi-cleavage fracture. The γ'phase morphology still maintained cubic shape after fracture. There were a number of slip bands shear the γ'precipitates and γ matrix near the fracture surface of the specimen. The inhomogeneous deformation microstructure was developed by dislocation motion of cross-slip and a limited γ'precipitate shearing by slip band, stacking faults or single dislocation was observed.

关键词： Single crystal superalloy LCF Fracture mechanism Microstructure

Influence of Ru Content on Microstructural Stability and Stress Rupture Property of DD15 Alloy

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Journal of Harbin Institute of Technology(New Series) 2023年第6期30卷 29-34页

作者： Zhenxue Shi shizhong liu Science and Technology on Advanced High Temperature Structural Materials Laboratory Beijing Institute of Aeronautical MaterialsBeijing 100095China

A fourth generation single crystal(SC)nickel based cast superalloy DD15 with 1%Ru,3%Ru,5%Ru was prepared using vacuum induction single crystal furnace in order to optimize the properties and cost of DD15 *** exposure experiment of three alloys was conducted at 1100℃for 1000 *** stress rupture properties tests were performed at 1100℃temperature and 137 MPa *** composition optimization of Ru element in DD15 alloy had been *** was found that the alloys with different Ru contents all consist of cuboidalγ′phase embedded coherent inγ***γ′phase of the alloy all has a size of about 300-500 nm and a volume content of more than sixty *** dimension ofγ′precipitates is reduced and uniform with increase of Ru *** element can reduce the distribution ratio of high melting point element,so the microstructural stability is enhanced with Ru content *** topologically close-packed(TCP)phase precipitated in the 5%Ru alloy even after 1000 h *** stress rupture life of the alloy is significantly improved as Ru content *** raft breadth decreases slightly as Ru content *** specimen with 1%Ru and 3%Ru exhibits the presence of TCP phases and without TCP phases precipitated in fracture specimen with 5%*** density and integrity ofγ/γ′interfacial dislocation network increase as Ru content of the alloy rises.

关键词： DD15 alloy Ru element stress rupture life microstructure stability

Effects of Rhenium on Creep Rupture Life of a Single Crystal Superalloys

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Journal of Materials Science & Technology 1999年第1期15卷 53-57页

作者： Li, Jiarong Tang, Dingzhong Lao, Riling liu, shizhong Wu, Zhongtang Inst Aeronaut Mat Beijing 100095 Peoples R China

The slabs of a single crystal superalloy were poured with 2.2%Re, 3.2%Re and 4.2%Re and other element contents of the alloys were basically kept unchanged. The effects of Re on the ultimate tensile strength, creep rupture life and rafting of a single crystal superalloy were studied. The results show that with increasing Re content the ultimate tensile strength decreases but the plasticity increases at 982 degree C/248.2 MPa, 1038 degree C/206.8 MPa and 1070 degree C/176.8 MPa for the alloy; on the microstructure aspect, with increasing the creep rupture life of the alloy the rafting is getting bigger and bigger at the same test condition, and the rafting suppresses creep and increases creep rupture life in the single crystal superalloy. (Edited author abstract) 11 Refs.

关键词： Superalloys

Solidification Simulation of Single Crystal Investment Castings

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Journal of Materials Science & Technology 2002年第4期18卷 315-318页

作者： Jiarong LI, shizhong liu and Zhengang ZHONGBeijing Institute of Aeronautical Materials, Beijing 100095, China Beijing Inst. of Aero. Mat. Beijing 100095 China

The three dimensional solidification simulation of the single crystal investment castings at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7 mm祄in was performed with the finite element thermal analysis method. The calculated results were in accordance with the experimental ones. The results showed that with the increase of with-drawal rate the concave curvature of the liquidus isotherm was bigger and bigger and the temperature gradient of the castings decreased. No effects of withdrawal rate on the distribution of the temperature gradient of the starter and helical grain selector of the castings were observed at withdrawal rates of 2 mm祄in, 4.5 mm祄in and 7mm祄in. The relatively high temperature gradient between 500癈礳m and 1000癈礳m in the starter and helical grain selector was obtained at three withdrawal rates. The study indicates the three dimensional solidification simulation by finite element method is a powerful tool for understanding solidification and predicting defects in single crystal investment castings.

关键词： Single crystal Investment casting Solidification simulation

Effects of precipitation on soil organic carbon fractions in three subtropical forests in southern China

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Journal of Plant Ecology 2016年第1期9卷 10-19页

作者： Xiaomei Chen Deqiang Zhang Guohua Liang Qingyan Qiu Juxiu liu Guoyi Zhou shizhong liu Guowei Chu Junhua Yan School of Geographical Sciences Guangzhou UniversityGuangzhou 510006China South China Botanical Garden Chinese Academy of SciencesGuangzhou 510650China State Key Laboratory of Conservation and Utilization of Subtropical Agro-Bioresources South China Agricultural UniversityGuangzhou 510650China University of Chinese Academy of Sciences Beijing 100039China

Aims The aim of this study was to investigate the effects of precipitation changes on soil organic carbon(SOC)fractions in subtropical forests where the precipitation pattern has been altered for *** We conducted field manipulations of precipitation,including ambient precipitation as a control(CK),double precipitation(DP)and no precipitation(NP),for 3 years in three forests with different stand ages(broadleaf forest[BF],mixed forest[MF]and pine forest[PF])in subtropical *** the end of the experiment,soil samples were collected to assay SOC content,readily oxidizable organic carbon(ROC)and non-readily oxidizable organic carbon(NROC),as well as soil microbial biomass carbon(MBC),pH and total nitrogen *** from the forest floors were also collected to analyze carbon(C)functional groups(*** C,aromatic C,O-alkyl C and carbonyl C).Furthermore,fine root biomass was measured periodically throughout the *** Findings Among the forests,ROC content did not exhibit any notable differences,while NROC content increased significantly with the stand *** finding implied that the SOC accumulation observed in these forests resulted from the accumulation of NROC in the soil,a mechanism for SOC accumulation in the mature forests of southern ***,NP treatment led to significant reductions in both ROC and NROC content and therefore reduced the total SOC content in all of the studied *** decreases may be due to the lower plant-derived C inputs(C quantity)and to the changes in SOC components(C quality)indicated by C functional groups analyses under NP *** treatment in all the forests also tended to decrease the SOC content,although the decreases were not statistically significant with the exception of SOC and ROC content in *** finding indicated that soils in MF and in BF may be more resistant to precipitation increases,possibly due to less water limitations under natural conditions in the two ***

关键词： rainfall pattern labile organic carbon soil organic carbon stable organic carbon forest floor

Tibetan Treasures Showrin USA

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China's Tibet 2004年第6期15卷 12-14页

作者： liu shizhong

From October 2003 to September 2005, China holds the Tibet: Treasures From the Roof of the World show in Los Angeles, Huston, San Francisco, New York and other American cities.

关键词：美国西藏珍品展历史文化博物馆宗教信仰

Influence of Ru Level on Microstructural Stability and Creep Rupture Property of DD15 Alloy

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Journal of Harbin Institute of Technology(New series) 2023年

作者： Zhenxue Shi shizhong liu Science and Technology on Advanced High Temperature Structural Materials Laboratory，Beijing Institute of Aeronautical Materials

A fourth generation single crystal (SC) nickel based cast superalloy DD15 with 1%Ru， 3%Ru， 5%Ru was prepared using vacuum induction single crystal furnace in order to optimize the properties and cost of DD15 alloy. The exposure experiment of three alloys was conducted at 1100 ℃ for 1000 h. The stress rupture properties tests were performed at 1100 ℃ temperature and 137 MPa pressure. The composition optimization of Ru element in DD15 alloy had been studied. It was found that the alloys with different Ru contents all consist of cuboidal γ′ phase embedded coherent in γ phase. The γ′ phase of the alloy all has a size of about 300-500 nm and a volume content of more than sixty percent. The dimension of γ′ precipitates is reduced and uniform with increase of Ru content. Ru element can reduce the distribution ratio of high melting point element， so the microstructural stability is enhanced with Ru content increasing. No topologically close-packed (TCP) phase precipitated in the 5% Ru alloy even after 1000 h exposure. The creep rupture life of the alloy is significantly improved as Ru content rising. The raft breadth decreases slightly as Ru content increases. The specimen with 1% Ru and 3% Ru exhibits the presence of TCP phases and without TCP phases precipitated in fracture specimen with 5% Ru. The density and integrity of γ/γ′ interfacial dislocation network increas as Ru content of the alloy rises.

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Solidification Simulation of Investment Castings of Single Crystal Hollow Turbine Blade

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Journal of Materials Science & Technology 2003年第6期19卷 532-534页

作者： Jiarong LI, shizhong liu, Hailong YUAN and Zhengang ZHONGNational Key Laboratory of Advanced High Temperature Structural Materials, Beijing Institute of Aeronautical Materials, Beijing 100095, China Lab. of Adv. High Temp. Mat. Beijing Inst. of Aero. Mat. Beijing 100095 China

The three-dimensional solidification simulation of the investment castings of single crystal hollow turbine blade at the withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min has been performed with the finite element thermal analysis. The calculated results are in accordance with the experimental ones. The results show that with the increase of withdrawal rate the concave curvature of the liquidus isotherm is larger and larger, and the temperature gradients of the blades increase. No effects of withdrawal rate on the distribution of the temperature gradients of the starter and helical grain selector of the blades are observed at withdrawal rates of 2 mm/min, 4.5 mm/min and 7 mm/min. The relatively high temperature gradient between 500℃/cm and 1000℃/cm in the starter and helical grain selector is obtained at three withdrawal rates.

关键词： Single crystal Hollow turbine blade Solidification simulation

Effect of long term aging on microstructure and stress rupture properties of a nickel based single crystal superalloy

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Progress in Natural Science:Materials International 2012年第5期22卷 426-432页

作者： Zhenxue Shi,Jiarong Li,shizhong liu Science and Technology on Advanced High Temperature Structural Materials Laboratory,Beijing Institute of Aeronautical Materials,Beijing 100095,China Science and Technology on Advanced High Temperature Structural Materials Laboratory Beijing Institute of Aeronautical Materials Beijing 100095 China

A nickel based single crystal superalloy with [001] orientation was prepared by the screw selecting method in the directionally solidified *** long term aging(LTA) of the alloy after full heat treatment was performed at 1040℃ for 200-800 *** microstructure and stress rupture properties at 980℃/250 MPa and 1070℃/140 MPa of the alloy long term aged(LTAed) for different time were *** coarsening γ’ phase and the broadening g matrix channel are observed in the samples LTAed at 1040℃,but the γ’ morphology is still in cubic shape after LTA for 800 *** TCP phase precipitates after LTA for 400 h,while needle shaped and granular TCP phase forms in dendritic core of the alloy after LTA for 600 *** increasing aging time,the volume of the TCP phase increases and it grows from the dendritic core to the interdendritic region along a fixed *** composition of the TCP phase is mainly composed of Re and *** increasing aging time the rupture life of the alloy at 980℃/250 MPa and 1070℃/140 MPa all turns ***,the relationship between the microstructure and the stress rupture properties is discussed.

关键词： Single crystal superalloy Long term aging(LTA) Microstructure Stress rupture properties