Generation mechanism and motion behavior of sliver defect in single crystal Ni-based superalloy  

作　　者：Huxiang Xia Yanhong Yang Qiushui Feng Qingyan Xu Hongbiao Dong Baicheng Liu 

机构地区：[1]Key Laboratory for Advanced Materials Processing Technology(MOE),School of Materials Science and Engineering,Tsinghua University,Beijing,100084,China [2]Shi-changxu Innovation Center for Advanced Materials,Institute of Metal Research,Chinese Academy of Sciences,Shenyang,110016,China [3]School of Engineering,University of Leicester,Leicester,LE17RH,United Kingdom

出　　处：《Journal of Materials Science & Technology》2023年第6期232-246,共15页材料科学技术（英文版）

基　　金：This work was financially supported by the National Science and Technology Major Project(Nos.2017-VⅠ-0003-0073 and 2017-Ⅶ-0008-0101).The authors are grateful to Prof.Yao Kefu and Miss.Liao Yang in Tsinghua University for the assistance and advice with the analysis of TEM results.

摘　　要：Sliver is a common but easily neglected defect in single crystal Ni-based superalloy castings.To date,there is still no unified viewpoint on its formation mechanism and generation causes.In this work,the orientation discontinuity and motion behavior of sliver defects were studied through experiments and numerical simulations.The ultrathin wedge-shaped specimen containing the grain boundary of the sliver and the matrix was prepared at the initial position of the sliver defect for the observation of equal thick-ness fringes.The discontinuity of equal thickness fringes on both sides of the grain boundary was ob-served through a transmission electron microscope,which directly confirms the abrupt change in the orientation between the sliver and matrix from the nanoscale.The crystal lattices at the smooth area and the bulging area of the grain boundary were found to have unusually different arrangements.The irregular lattice arrangement at the bulging area shows that the grain boundary has experienced high-stress deformation.Statistical results of sliver orientation deviation with a further composition analysis show the micro protuberance of the mold shell has a noticeable inductive effect on the sliver generation.Furthermore,a self-developed three-dimensional phase-field simulation model coupled with the spatial topology algorithm is established to simulate the orientation deflection behavior and orientation devia-tion threshold of fractured dendrites.The simulation results indicated that there is an upper limit of the cross-section solid fraction at the fracture position for the motion of the fractured dendrites.When the cross-section solid fraction at the fracture position is higher than this upper limit,it will be difficult to produce large deviation slivers due to the structural limitation of surrounding dendrites.This upper limit does not change with the solidification temperature gradient.

关 键 词：Single crystal Ni-based superalloys Directional solidification Sliver defect Phase-field simulation 

分 类 号：TG132.3[一般工业技术—材料科学与工程]