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Retarding the precipitation of η phase in Fe-Ni based alloy through grain boundary engineering

Journal of Materials Science & Technology 2020年第12期47卷 152-161页

作者： Honglei Hu Mingjiu Zhao Lijian Rong Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Materials Science and Engineering University of Science and Technology of China96 Jinzhai RoadHefei 230026China

It is important to inhibit the precipitation of η phases in precipitation strengthened Fe-Ni based alloys,as they will deteriorate not only the mechanical property but also the hydrogen resistance.The present investigation shows that grain boundary engineering(GBE) can retard the formation and growth of ηphase in J75 alloy.After GBE treatment with 5% cold rolling followed by annealing at 1000℃ for 1 h,the fraction of special boundaries(SBs) increases from 38.4% in conventional alloy to 77.2% and the fraction of special triple junctions increases from 10% to 74%.During 800℃ aging treatment,quite amount of cellular η phases adjacent to random grain boundary(RGB) will be found in conventional alloy,and only a few small η phases have been observed in GBE treatment alloy subjected to the same aging treatment for long time.The reason for GBE in inhibiting precipitation of η phase can be attributed to not only introducing high fraction of SBs but also breaking the connectivity of RGB networks.As nucleation and growth of η phases on SBs are difficult due to their lower Ti concentration and diffusion rate,and the disruption of RGB networks reduces supply of Ti atoms to the η phases significantly,which impedes their growth at RGB.

关键词： Fe-Ni based alloy ηphase Precipitation behavior Random grain boundary connectivity Grain boundary engineering Boundary diffusion

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Effect of stabilizing treatment on microstructure and stress rupture properties of phosphorus microalloyed Inconel 706 alloy

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Journal of Iron and Steel Research(International) 2023年第8期30卷 1613-1621页

作者： Sha Zhang Yu-chao Wu Yu Lil Zhong-pei Dail Dan Jia Yan-fei Xu Guang-sheng Zeng Zhi-ming Guo Jian Liul College of Mechanical&Electrical Engineering Changsha UniversityChangsha 410022HunanChina Hunan Engineering Research Center of Research and Development of Degradable Materials and Molding Technology Changsha UniversityChangsha 410022HunanChina Changsha Kaiple Technology Co. Ltd.Changsha 410114HunanChina Institute of Metal Research Chinese Academy of SciencesShenyang 110016LiaoningChina

The microstructure and stress rupture properties of Inconel 706 alloy microalloyed with phosphorus are examined under stabilizing and unstabilizing heat treatment conditions.It was found that applying the stabilizing treatment resulted in a 98% increment in the stress rupture life and a 215% increment in the elongation tested at 650℃/690 MPa for the alloy compared to that under the unstabilizing heat treatment condition.The stabilizing treatment led to the precipitation of rod-shaped and needle-shaped n phases at the grain boundaries.Morphologies of γ'-γ" co-precipitates in the grain interior were noncompact form and compact form for the alloy under unstabilizing and stabilizing heat treatment conditions,respectively.Based on the microstructure characterizations,the improvement of stress rupture properties by the stabilizing treatment was attributed to the precipitation of n phases at the grain boundaries,which can hinder cracks initiation and propagation and relieve the stress concentration.

关键词： Superalloy Stabilization ηphase γ'-γ"co-precipitate Stress rupture property

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Precipitates evolution and tensile behavior of wrought Ni-based ATI 718Plus superalloy during long-term thermal exposure

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Science China(Technological Sciences) 2022年第6期65卷 1283-1299页

作者： GUO QianYing JI KangKang ZHANG Teng QIAO ZhiXia LI Chong LI Jun LIU ChenXi LIU YongChang State Key Laboratory of Hydraulic Engineering Simulation and Safety School of Materials Science and EngineeringTianjin UniversityTianjin 300354China Southwestern Institute of Physics Chengdu 610041China School of Mechanical Engineering Tianjin University of CommerceTianjin 300134China

In this paper,the microstructure evolution and tensile behavior of wrought ATI 718 Plus superalloy during long-term thermal exposure(LTTE) were investigated.The γ’ phase evolves from spherical morphology to cuboidal morphology at 800℃,which is related to increasing γ’/γ misfit because of the increase of elastic energy.The amounts of η phase obviously increased and γ’ precipitate free zones(PFZs) were found in 800-LTTE samples due to the increase of η phase amount by consuming Al,Ti,and Nb.According to the formula of “MC+γ→M_(23)C_(6)+η”,η phase is also related to the decomposition of MC carbide,which involves the diffusion and segregation of Nb and Ti.In addition,some short rod-like and irregular Cr,Mo-rich σ phases were prone to precipitate near η phases after LTTE at 800℃ for 500 and 1000 h.σ phase has a crystallographic relationship with ηphase as(002)_(σ)//(10■0)_(η),[0■0]_(σ)//[01■0]_(η).The deteriorated tensile strength after LTTE is mainly attributed to that:(1) the evident coarsening of γ’ phase results in that the deformation mechanism transforms from stacking faults(SFs) shearing to Orowan looping,which is also convinced by calculated critical resolved shear stress(CRSS);(2) the noticeable increasing number of η phase contributes to stress concentration,resulting in micro-cracks formation;and (3) the apparently increasing number of η phase promotes the PFZs formation.

关键词： ATI 718Plus superalloy long-term thermal exposure γ’coarsening ηphase σphase deformation mechanism

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Effect of grain boundary precipitates on the stress rupture properties of K4750 alloy after long-term aging at 750℃for 8000 h

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Journal of Materials Science & Technology 2021年第33期92卷 11-20页

作者： Meiqiong Ou Yingche Ma Kunlei Hou Min Wang Guangcai Ma Kui Liu Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Materials Science and Engineering University of Science and Technology of ChinaHefei 230026China

In K4750 alloy,the evolution of grain boundary(GB)precipitates,including the degradation of blocky MC carbide particles and the precipitation of granular/needle-likeηphase particles,were observed after longterm aging(LA)at 750℃for 8000 h.During MC degradation,the Ti and C released from the MC carbide combined with Ni and Cr,respectively,in theγ’matrix to formη-Ni_(3)Ti phase and Cr-rich M_(23)C_(6)carbide.Large amounts of granularηphase precipitated at GBs and the needle-likeηphase grew gradually from GBs toward the grain interior.Because of the growth of theηphase through absorbingγ’phase,γ-depleted zones were formed around theηphase.The evolution of the MC carbide andηphase was primarily responsible for the decrease of the stress rupture life and the increase of elongation.After an LA sample was tested at 750℃and 360 MPa,the residual strain distribution was investigated by electron backscatter diffraction(EBSD).The results showed that the residual strain mainly distributed at GBs,especially in the region of MC degradation and at the edges ofηphases,which was closely related to the appearance of phase interfaces.Microvoids/cracks easily initiated at phase interfaces,then easily extended along theγ-depleted zones,thus the stress rupture life of LA samples was substantially shorter than that of samples subjected to the standard treatment.In particular,because of large amounts of fine degraded MC,granular M_(23)C_(6)and granularηphase particles distributed at GBs after 750℃/8000 h LA and microvoid/crack formation could be hindered by the formation of dimples,which led to an increase of elongation.

关键词： Ni-base superalloy Long-term aging,MC carbide ηphase Stress rupture properties Residual strain distribution

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