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

作　　者：Meiqiong Ou Yingche Ma Kunlei Hou Min Wang Guangcai Ma Kui Liu 

机构地区：[1]Shi-changxu Innovation Center for Advanced Materials,Institute of Metal Research,Chinese Academy of Sciences,Shenyang 110016,China [2]School of Materials Science and Engineering,University of Science and Technology of China,Hefei 230026,China

出　　处：《Journal of Materials Science & Technology》2021年第33期11-20,共10页材料科学技术（英文版）

基　　金：supported by the National Natural Science Foundation of China under Grant No.52001314;the Natural Science Foundation of Liaoning Province of China under Grant No.2020BS-008;the China Postdoctoral Science Foundation under Grant No.2020M671403。

摘　　要：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 

分 类 号：TG156.92[金属学及工艺—热处理] TG132.3[金属学及工艺—金属学]