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Interaction between γ'precipitate distribution and microstructure homogeneity during hot deformation in a Ni-based superalloy

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Journal of Iron and Steel Research(International) 2023年第11期30卷 2301-2317页

作者： Cheng-yu Wang Teng An Yu Gu Zhong-nan Bi Jin-hui Du Jing-long Qu Beijing Key Laboratory of Advanced High Temperature Materials Central Iron&Steel Research InstituteBeijing100081China Beijing GAONA Materials&Technology Co. Ltd.Beijing100081China

The inhomogeneous microstructure of the Ni-based superalloys used for turbine disks was an intolerable defect for the mechanical performance.The effects of the distribution ofγ'precipitate,forging temperature,and strain level on the microstructure evolution of GH4730 alloy were investigated by EBSD during hot deformation.The results showed that the heterogeneous factor peaked at the transition temperature from the single-phase to the double-phase region.The coupling effect of heat and stress led to the heterogeneous precipitation and distribution ofγ'phase during the transition region,which was the main reason for the formation of inhomogeneous microstructures.The coherentγ'phases of approximately 0.3μm were diffusely distributed inside the large grains,increasing the grain strength,making recrystallization refinement difficult,and thus forming large unrecrystallized grains.The incoherentγ'phases with a size of approximately 1.1μm located at the grain boundaries and pinned the grain boundaries,and thus the accumulated strain at the grain boundaries caused the occurrence of discontinuous dynamic recrystallization and promoted continuous refinement of the grains.The microstructure evolution of new Ni-based superalloys during hot forging was focused,and the formation mechanism of inhomogeneous microstructure and control measures was explained.A theoretical basis for improving the microstructure homogeneity of the new cast and wrought superalloys was provided.

关键词： GH4730 alloy Hot deformation γ′phase Heterogeneous factor Microstructure homogeneity

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Evolution mechanism of recrystallization in a nickel-based single crystal superalloy under various cooling rates during heat treatment

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China Foundry 2022年第1期19卷 27-34页

作者： Yong-shun Li Wei-dong Xuan Jian Yang Yu-hao Zhou Ge Song Xing-fu Ren Zhong-ming Ren State Key Laboratory of Advanced Special Steel&Shanghai Key Laboratory of Advanced Ferrometallurgy&School of Materials Science and Engineering Shanghai UniversityShanghai 200444China School of Medicine Shanghai UniversityShanghai 200444China

The recrystallization behaviors of a nickel-based single crystal superalloy during heat treatment at 1,200℃ for 4 h with various cooling rates were studied.Results show that the thickness of recrystallization layer decreases with the increase of cooling rate.In addition,the microstructures ofγ′phase in the recrystallization region are different in various cooling rates.In the high cooling rates(70,100℃·min^(-1)),small size and high volume fraction ofγ′phases are formed in the recrystallization region.It is also found that irregular fine secondaryγ′phases are precipitated between matrix channels with an average size of 150 nm in the original matric(100℃·min^(-1)).The sizes of the secondaryγ′phase decrease with the increase of cooling rate.In contrast,large size and small volume fraction ofγ′phases are formed in the recrystallization region,and a grain boundary layer is formed under a low cooling rate(10℃·min^(-1)).The evolution mechanism of recrystallization at various cooling rates during heat treatment is analyzed.

关键词： recrystallization cooling rate γ′phase single crystal superalloy

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Investigation on the homogenization treatment and element segregation on the microstructure of a γ/γ′-cobalt-based superalloy

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International Journal of Minerals,Metallurgy and Materials 2019年第2期26卷 222-233页

作者： Saeed Aliakbari Sani Hossein Arabi Shahram Kheirandish Golamreza Ebrahimi School of Materials and Metallurgical Engineering Iran University of Science and Technology ((IUST)) School of Materials and Metallurgical Engineering Iran University of Science and Technology (IUST) Materials and Polymers Engineering Department Faculty of Engineering Hakim Sabzevari University

The aim of the present study was to investigate the effect of element segregation on the microstructure and γ′ phase in a γ/γ′ cobalt-based superalloy. Several samples were prepared from a cast alloy and homogenized at 1300°C for different times, with a maximum of 24 h. A microstructural study of the cast alloy using wavelength-dispersive spectroscopic analysis revealed that elements such as Al, Ti, and Ni segregated mostly within interdendritic regions, whereas W atoms were segregated within dendrite cores. With an increase in homogenization time, segregation decreased and the initial dendritic structure was eliminated. Field-emission scanning electron microscopy micrographs showed that the γ′ phases in the cores and interdendritic regions of the as-cast alloy were 392 and 124 nm, respectively. The size difference of γ′ was found to be due to the different segregation behaviors of constituent elements during solidification. After homogenization, particularly after 16 h, segregation decreased; thus, the size, chemical composition, and hardness of the precipitated γ′ phase was mostly uniform throughout the samples.

关键词： superalloy segregation homogenization microstructure γ′phase

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Influences of processing parameters on microstructure during investment casting of nickel-base single crystal superalloy DD3

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China Foundry 2012年第2期9卷 159-164页

作者： Gao Sifeng Liu Lin Xu Yiku Yang Chubin Zhang Jun Fu Hengzhi State Key Laboratory of Solidification Processing Northwestern Polytechnic UniversityXi'an 710072China

The effects of solidification variables on the as-cast microstructures of nickel-base single crystal superalloy DD3 have been investigated by using the modified Bridgman apparatus.The experiments were performed under a thermal gradient of approximately 45 K·cm-1 and at withdrawal rates ranging from 30 to 200 m·s-1.The experimental results show that the primary and secondary dendritic arm spacings(PDAS and SDAS) decrease when the withdrawal rate is increased.Compared with the theoretical models of PDAS,the results are in good agreement with Trivedi's model.The relationships of PDAS and SDAS with withdrawal rates can be described as ? 1 =649.7V -0.24±0.02 and? 2 =281V -0.32±0.03 ,respectively.In addition,the size of theγ′phase significantly decreases with increasing withdrawal rate.

关键词： Ni-base superalloys directional solidification γ′phase dendritic spacing

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