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A review on solidification of alloys under hypergravity

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Progress in Natural Science:Materials International 2023年第3期33卷 279-294页

作者： Fangjie You xinbao zhao Quanzhao Yue Yuefeng Gu Jiahui Wang Hongbin Bei Ze Zhang Institute of Superalloys Science and Technology School of Materials Science and Engineering Zhejiang University State Key Laboratory of Silicon and Advanced Semiconductor Materials Zhejiang University Polytechnic Institute Zhejiang University

A comprehensive and integrated review of the hypergravity field applied to solidifying alloys is provided. The hypergravity field refers to an environment in which the acceleration of gravity is more significant than the gravitational acceleration through rotation, resulting in significant changes in the solidification behavior of the alloy. The convection mode of the melt is closely related to the level and direction of hypergravity. Obvious floatation or sedimentation of solutes and crystals of different densities is induced. Columnar-to-equiaxed transition, grain refinement, and gradients in composition and microstructure are readily available under hypergravity. Furthermore, the nucleation and growth of crystals and their migration under enhanced convection are gradually revealed through simulations and in-situ observations. This review aims to summarize the universal law of the effect of the hypergravity field on the composition distribution and microstructure evolution of alloys during solidification. Based on the development of hypergravity equipment and characterization methods, it is expected to broaden the theoretical framework of hypergravity solidification. To provide a theoretical reference for developing new solidification processes and high-performance materials.

关键词： Hypergravity Solidification Alloys Grain refinement Convection Segregation

Aging process design based on the morphological evolution ofγprecipitates in a 4th generation nickel-based single crystal superalloy

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Journal of Materials Science & Technology 2023年第16期147卷 176-188页

作者： Jiachen Xu xinbao zhao Weiqi Li Hao Liu Quanzhao Yue Huanchang Duan Yuefeng Gu Ze Zhang Institute of Superalloys Science and Technology School of Materials Science and EngineeringZhejiang UniversityHangzhou 310027ZhejiangChina Polytechnic Institute Zhejiang UniversityHangzhou 310027ZhejiangChina

In order to meet the design requirements of the aging treatment process of a 4th generation nickel-based single crystal superalloy(Ni-SX)developed independently,the effects of aging temperatures and aging times on the precipitation and morphological evolution ofγprecipitates are studied.The morphological evolution behavior ofγprecipitates during the aging process is summarized subsequently and the coarsening behavior ofγprecipitates is discussed by comparing with the Lifshitz-Slyozov-Wagner model(LSW)and the trans-interface diffusion-controlled model(TIDC).It is demonstrated that primary aging temperature and secondary aging time dominate the size and squareness ofγprecipitates respectively,a narrow primary aging temperature range and a suitable secondary aging time are allowed to obtain the optimized morphology ofγprecipitates.The optimal aging process of the Ni-SX investigated in the present work is obtained for 1100-1120°C/4 h and 870°C/16 h,confirmed by the corresponding creep tests.The coarsening growth ofγprecipitates in short-term aging also conforms to the LSW model well.Besides,the aging process design rules of various Ni-SXs of different generations are also summarized.

关键词： Nickel-based single crystal superalloy Aging temperature Aging time γprecipitates Creep

Impacts of different designed microstructures on creep performance of a Ni-based wrought superalloy

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Progress in Natural Science:Materials International 2023年第5期33卷 625-633页

作者： Hao Liu xinbao zhao Yuan Cheng Jiachen Xu Shuhao Cheng Quanzhao Yue Yong Yuan Yuefeng Gu Ze Zhang Institute of Superalloys Science and Technology School of Materials Science and Engineering Zhejiang University Polytechnic Institute Zhejiang University State Key Laboratory of Silicon and Advanced Semiconductor Materials Zhejiang University Xi'an Thermal Power Research Institute Co.Ltd.

The creep behavior of a novel Ni-based wrought superalloy with varying aging states, classified as large underaged(UA), little UA, and little over-aged(OA) states, was investigated at a temperature higher than the intragrain/grain-boundary iso-strength temperature(750°C/250 MPa). In the samples before creep test, there are spherical γ’precipitates homogeneously dispersed within the γ matrix and carbides precipitated at grain boundaries(GBs). After creep tests, precipitate-free zones(PFZs) appear on grain boundaries, with a large blocklike γ’phase present between carbides and PFZs, potentially serving as initiation sites for cracks. Little UA state samples exhibit the strongest creep resistance and intergranular fracture. The dominant creep deformation mechanism in the intra-grain is a combination of Orowan process involving slip and climb of matrix dislocations and shearing of γ’precipitates. The results indicate that the optimizing the grain boundary microstructure may be more important than the change of intragranular microstructure when the creep temperature exceeds the isostrength temperature.

关键词： Ni-based wrought superalloy Intragranular microstructure Creep performance

A review of composition evolution in Ni-based single crystal superalloys

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Journal of Materials Science & Technology 2020年第9期44卷 76-95页

作者： Wanshun Xia xinbao zhao Liang Yue Ze Zhang Institute of Superalloys Science and Technology School of Materials Science and EngineeringZhejiang UniversityHangzhou310027China Center of Electron Miscroscopy Zhejiang UniversityHangzhou310027China

Due to the outstanding creep performance, nickel-based single crystal superalloys(Ni-SXs) are extensively applied in modern aero-engine and industrial gas turbine. Apart from the special single crystal structure which is disadvantageous to extension of creep cracks, Ni-SXs derive the creep strength from intrinsic two-phase microstructure(γ phase and γ’ phase). Main microstructural parameters including volume fraction of γ’ phase and the lattice misfit, and the formation and distribution of precipitated phase are determined by the compositions of alloys. Besides, the creep properties are greatly influenced by these microstructural parameters and precipitated phase. This review has summarized the relationships between different alloying elements and microstructures and indicated their influence on creep properties of Ni-SXs. In addition, with the improvements of experimental methods and characterization technique, some recent discoveries have provided additional evidence to support or challenge the pervious creep theories of superalloys. In view of these new discoveries, this review has provided some perspectives which can be referenced in future compositional design of Ni-SXs.

关键词： Nickel-based single crystal superalloys Composition Creep properties Refractory elements

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Inconsistent creep between dendrite core and interdendritic region under different degrees of elemental inhomogeneity in nickel-based single crystal superalloys

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Journal of Materials Science & Technology 2021年第33期92卷 88-97页

作者： Wanshun Xia xinbao zhao Liang Yue Quanzhao Yue Jiangwei Wang Qingqing Ding Hongbin Bei Ze Zhang Institute of Superalloys Science and Technology School of Materials Science and EngineeringZhejiang UniversityHangzhou 310027China Zhejiang Univ Ctr Electron MicroscopyHangzhou 310027China

The creep inconsistency between dendrite core and interdendritic region is investigated in a nickel-based single crystal superalloy under 1373 K and 137 MPa.Two specimens with higher and lower degree of elemental inhomogeneity on dendritic structures are compared.For specimen with higher inhomogeneity,stronger segregation of refractory elements reinforces the local strength in dendrite core,but damages the strength in interdendritic region.Creep strain is accumulated faster in interdendritic region giving rise to promoted dislocation shearing inγphase,faster degradation of dislocation networks and facilitated topological inversion of rated structures.Although the segregation of refractory elements produces a high density of topologically close-packed(TCP)phase in dendrite core,faster accumulation of creep strain forms microcracks prior in interdendritic region that gives rise to final rupture of the specimen.In another specimen,increased solid solution time gives rise to overall reduced inhomogeneity.Creep inconsistency is relieved to show more uniform evolution of dislocation substructures and rafting between dendrite core and interdendritic region.The second specimen is ruptured by formation and extension of microcracks along TCP phase although the precipitation of TCP phase is relatively restricted under reduced inhomogeneity.Importantly,the balance of local strength between dendrite core and interdendritic region results in over 40%increase of creep rupture life of the second specimen.

关键词： Nickel-based single crystal superalloys Dendritic structure Inhomogeneity Creep Rafting Dislocation networks

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The dependence of stress and strain rate on the deformation behavior of a Ni‐based single crystal superalloy at 1050°C

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International Journal of Mechanical System Dynamics 2021年第1期1卷 121-131页

作者： Qingqing Ding Hongbin Bei Lulu Li Jie Ouyang xinbao zhao Xiao Wei Ze Zhang School of Materials Science and Engineering Zhejiang UniversityHangzhouChina Polytechnic Institute Zhejiang UniversityHangzhouChina

Ni‐based single crystal(SX)superalloys are important high‐temperature materials used for manufacturing turbine blades in aero‐engines.During service under combinational impacts of temperature and stress,the SX superalloy may reach its life due to plastic deformation,which normally accompanies time‐dependent microstructural degradation.To reveal this dynamically mechanical response,tensile tests at 1050°C are carried out to record stress‐strain curves at five stain rates as well as creep curves at four applied stresses.Deformed microstructures and defects have been analyzed to understand mechanical behaviors and the underlying mechanism by using advanced scanning electron and scanning transmission electron microscopes.Results show that the de-formation mode of the alloy strongly depends on the strain rates/applied stresses under mechanical loading.The dislocation density inside theγphase is extremely low at all tests,indicating that theγphase is relatively weak and ready to flow at this temperature even at a very fast strain rate.The deformation behavior of theγ′phase is much complicated.At fast strain rates or high applied stresses,the dislocation density in theγ′phase is very high,contributing to high‐stress requirements to deform the material.At slow strain rates or low applied stresses,rafting microstructures develop and the de-formation mode becomes directional coarsening/diffusion‐dominated.Our results de-monstrate a comprehensive understanding of the deformation mechanism of Ni‐based SX superalloys,which may provide lifetime prediction of the mechanical fail-ure,as well as the database for superalloy applications in mechanical systems.

关键词： creep defects deformation behavior microstructure Ni‐based single crystal superalloy strain rate sensitivity

Influence of withdrawal rate on the porosity in a third-generation Ni-based single crystal superalloy

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Progress in Natural Science:Materials International 2017年第2期27卷 236-243页

作者： Quanzhao Yue Lin Liu Wenchao Yang Taiwen Huang Jun Zhang Hengzhi Fu xinbao zhao State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi’an Thermal Power Research Institute Co. Ltd.

The influence of withdrawal rate on the porosity in a third-generation Ni-based single crystal superalloy was investigated by a quantitative evaluation method. The results showed that the withdrawal rate obviously effected on the average area fraction, number and diameter of porosities except their radius ratios. In consideration of the microstructure observation for dendrite arms, an optimized withdrawal rate was obtained with a minimum porosity level as about 125 μm s;. Simultaneously, a threshold value for the acceptance level of porosities might be set as about 0.1% in order to fulfill the requirements for Ni-based single crystal casting in laboratory scale. Finally, the formation reason of porosity was discussed and it was concluded that the feeding for the volume shrinkage of the last solidified eutectic liquids from the residual liquids and the isolating effect of the morphologies of dendrite arms might be two key factors in controlling the porosities level in Ni-based single crystal superalloy.

关键词： Superalloys Porosity Withdrawal rate Microstructure Quantitative evaluation

Effect of heat treatment on the microstructure of a Ni–Fe based superalloy for advanced ultra-supercritical power plant applications

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Progress in Natural Science:Materials International 2016年第2期26卷 204-209页

作者： xinbao zhao Yingying Dang Hongfei Yin Jintao Lu Yong Yuan Zhen Yang Jingbo Yan Yuefeng Gu Xi'an Thermal Power Research Institute Co. Ltd. National Energy R&D Center of Clean and High-Efficiency Fossil-Fired Power Generation Technology

The effect of heat treatment on the microstructure and microhardness of a Ni–Fe based superalloy for700 °C advanced ultra-supercritical coalfi red power plants was investigated. Results showed that the main phases in the alloy were γ, γ′, MC and M23C6, and no harmful phase was observed in the alloy.M23C6-type carbides discretely distributed nearby grain boundaries as the alloy was aged at above840 °C. The microhardness decreased with increasing aging temperature. The coarsening of γ′ led to the increment of microhardness at 780 °C and 810 °C for a short aging time, and a signi fi cant decrease in microhardness after aging at 840 °C. The aging temperature had more signi fi cant role on the microstructure than holding time. Therefore, to obtain optimum strengthening effect for this alloy, the aging temperature should not exceed 810 °C.

关键词： Ultra-supercritical power plant Ni – Fe based superalloy Heat treatment Microstructure Microhardness

Effect of cooling rates on dendrite spacings of directionally solidified DZ125 alloy under high thermal gradient

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Rare Metals 2009年第6期28卷 633-638页

作者： ZHANG Weiguo LIU Lin zhao xinbao HUANG Taiwen YU Zhuhuan QU Min FU Hengzhi State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

The dendrite morphologies and spacings of directionally solidified DZ125 superalloy were investigated under high thermal gradient about 500 K/cm. The results reveal that, with increasing cooling rate, both the spacings of primary and secondary dendrite arms decrease, and the dendrite morphologies transit from coarse to superfme dendrite. The secondary dendrite arms trend to be refined and be well developed, and the tertiary dendrite will occur. The predictions of the Kurz/Fisher model and the Hunt/Lu model accord basically with the experimental data for primary dendrite arm spacing. The regression equation of the primary dendrite arm spacings 21 and the cooling rate Vc is λ1 = 0.013 Vc^-0.32. The regression equation of the secondary dendrite arm spacing λ2 and the cooling rate Vc is λ2 = 0.00258 Vc^-0.31, which gives good agreement with the Feurer/Wunderlin model.

关键词： directional solidification superalloy thermal gradient cooling rate dendrite arm spacing

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