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Journal of Materials Science & Technology 2023年第28期159卷 112-124页

作者： Lirong Rong Min Wang Weiwei Xing Xianchao Hao Yingche Ma School of Materials Science and Engineering University of Science and Technology of Chin1Shenyang 110016China Shi-changxu Innovation Center for Advanced Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China CAS Key Laboratory of Nuclear Materials and Safety Assessment Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China

The microstructure and stress rupture properties of a new nickel-based cast superalloy were investigated with the cerium(Ce)additions of 0,19,50,96,150,and 300 ppm,respectively.The results indicated that Ce was mainly found in M C and M 23 C 6 carbides,and it was also found to exist in the form of cerium-rich phases or inclusions.According to the microstructure evidence,Ce promoted the formation of M C carbides and aggravated the inhomogeneity of M 23 C 6 carbides along grain boundaries.It was also identi-fied that the average sizes of primary and secondaryγ’phases all decreased with the rising Ce content.The acceleration of Ti,Nb,and C segregations during solidification was attributed to the influence of cerium on the variation of carbides along grain boundaries.The stress rupture life experienced a signifi-cant drop as the Ce content increased from 19 to 300 ppm.Explorations showed that the degradation was mainly attributed to the severe degradation of M C carbides and the easily forming micro-voids around them caused by the Ce addition.In addition to that,the increments in the inhomogeneous distribution of M 23 C 6 carbides at grain boundaries and the accelerated coarsening rate ofγ’phases both induced the fracture under complex stress conditions.

关键词： Nickel-based cast superalloy Cerium MC carbide stress rupture properties

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

Microstructure evolution and stress rupture properties of K4750 alloys with various B contents during long-term aging

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Journal of Materials Science & Technology 2021年第14期73卷 108-115页

作者： Xiaoxiao Li Meiqiong Ou Min Wang Xiang dong Zha Yingche Ma Kui Liu Institute of Metal Research Chinese Academy of SciencesShenyang110016China School of Materials Science and Engineering University of Science and Technology of ChinaHefei230026China

The relationship among B content,microstructure evolution and stress rupture properties of K4750 alloy during long-term aging were investigated.After aging at 800℃for 1000 h,the decomposition degree of MC carbides of K4750 alloys with 0 B,0.007 wt.%B and 0.010 wt.%B were basically identical,which indicated that B has no inhibition on MC carbide decomposition during long-term aging.The MC carbide decomposition was accompanied by the formation of M_(23)C_(6) carbides and a small number ofηphases,which was controlled by the outward diffusion of C and Ti combined with the inward diffusion of Ni and Cr from theγmatrix.In addition,M_(23)C_(6) carbides in boron-free alloy were in continuous chain and needle-likeηphases were precipitated near them,while M_(23)C_(6) carbides in boron-containing alloys remained in granular distribution and noηphases precipitation around them.Adding B could delay the agglomeration and coarsening of M_(23)C_(6) carbides during long-term aging,which was because the segregation of B at grain boundary retarded the diffusion of alloy elements,thus weakened the local fluctuation of chemical composition near grain boundary.The stress rupture samples of K4750 alloys with various B contents after aging at 800℃for 1000 h were tested at 750℃/380 MPa.The results indicated that the stress rupture properties of bo ron-containing alloys were significantly better than that of boron-free alloy,which could be attributed to the increase of grain boundary cohesion strength and the optimization of M_(23)C_(6) carbide distribution due to the addition of B.

关键词： Nickel-based superalloy Boron additions Long-term aging Grain boundary segregation stress rupture properties

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 furnace.The long term aging(LTA) of the alloy after full heat treatment was performed at 1040℃ for 200-800 h.The microstructure and stress rupture properties at 980℃/250 MPa and 1070℃/140 MPa of the alloy long term aged(LTAed) for different time were investigated.The 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 h.No 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 h.With increasing aging time,the volume of the TCP phase increases and it grows from the dendritic core to the interdendritic region along a fixed direction.The composition of the TCP phase is mainly composed of Re and W.With increasing aging time the rupture life of the alloy at 980℃/250 MPa and 1070℃/140 MPa all turns shorter.Finally,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

Rejuvenation Heat Treatment of the Second-Generation Single-Crystal Superalloy DD6

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Acta Metallurgica Sinica(English Letters) 2015年第10期28卷 1278-1285页

作者： Zhen-Xue Shi Shi-Zhong Liu Jia-Rong Li Science and Technology on Advanced High Temperature Structural Materials Laboratory Beijing Institute of Aeronautical Materials

The second-generation single-crystal superalloy DD6 with [001] orientation was prepared by screw selecting method in the directionally solidified furnace. The long-term aging of the alloy after full heat treatment was performed at1100 °C for 400 h. Then the rejuvenation heat treatment 1300 °C/4 h/AC ？ 1120 °C/4 h/AC ？ 870 °C/24 h/AC was carried out. The stress rupture properties were investigated at 760 °C/800 MPa, 850 °C/550 MPa, 980 °C/250 MPa and1100 °C/140 MPa after different heat treatments. The microstructures of the alloy at different conditions were studied by SEM. The results show that c0 phase of the alloy became very irregular and larger after long-term aging at 1100 °C for 400 h. A very small amount of needle-shaped TCP phase precipitated in the dendrite core. The coarsened c0 phase and TCP phase dissolved entirely after rejuvenation heat treatment. The microstructure was restored and almost same with the original microstructure. The stress rupture life of the alloy decreased in different degrees at various test conditions after long-term aging. The stress rupture life of the alloy after rejuvenation heat treatment all restores to the original specimen more than 80%at different conditions. The microstructure degradation of the alloy during long-term aging includes coarsening of the c0 phase,P-type raft and precipitation of TCP phase, which results in the degeneration of stress rupture property. The rejuvenation heat treatment succeeds in restoring the original microstructure and stress rupture properties of the alloy.

关键词： Single-crystal superalioy DD6 Rejuvenation heat treatment stress rupture properties

Influence of Carbon Content and Solidification Condition on Incipient Melting of DS Superalloy MAR-M200+2Hf

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Journal of Materials Science & Technology 1989年第2期5卷 90-95页

作者：郑运荣王罗宝李成功 Institute of Aeronautical Materials Beijing China.

Hf lowers the incipient melting temperature of superalloy. As carbon content in Hf-bearing alloy decreases, the incipient melting temperature drops furthey. PD ingots have stronger tendency to incipient melting than HRS ones. Even though in PD ingot, the sensitivities at both ends of the ingot are quite different. The melting of Ni_5Hf phase may be considered as one of the main factors affecting incipient melting. The more Ni_5Hf the alloy contains, the more serious the incipient melting becomes. The results of differential thermal analysis (DTA) have proved that the peak of 1135-1160℃ corresponds to the melting range or Ni_5Hf. By means of a pretreatment at 1150℃, 8h, Ni_5Hf phase can be eliminated in two ways: the reaction Ni_5Hf+γ(C)→MC_(2)+γ and solid solution, and therefore the final solid solution treatment can be carried out at 1260℃. This brings about a high homogenized structure and further increases the stress rupture properties of the alloy at 1040℃, 140 MPa.

关键词： DS superalloy hafnium incipient melting phase transformation heat treatment stress rupture properties