A quasi-in-situ EBSD study of the thermal stability and grain growth mechanisms of CoCrNi medium entropy alloy with gradient-nanograined structure  

作　　者：P.-C.Zhao B.Guan Y.-G.Tong R.-Z.Wang X.Li X.-C.Zhang S.-T.Tu 

机构地区：[1]Key Laboratory of Pressure Systems and Safety,Ministry of Education,School of Mechanical and Power Engineering,East China University of Science and Technology,Shanghai 200237,China [2]College of Materials Science and Engineering,Chongqing University,Chongqing 400044,China [3]College of Automobile and Mechanical Engineering,Changsha University of Science and Technology,Changsha,China

出　　处：《Journal of Materials Science & Technology》2022年第14期54-63,共10页材料科学技术（英文版）

基　　金：financial supports from the National Natural Science Foundation of China(Nos.51725503,52105144 and 52005185);Shanghai Super Postdoctoral Incentive Plan(No.2020134);Postdoctoral Fellowship for Research in Japan(FY2020 P20350)by the Japan Society for the Promotion of Science(JSPS)。

摘　　要：The thermal stability and mechanical properties of a gradient-nanograined structure(GNS)CoCrNi medium entropy alloy(MEA)processed by ultrasonic surface rolling were studied by using isothermal/isochronal annealing tests combined with quasi-in-situ electron backscatter diffraction(EBSD)characterization and Vickers micro-hardness(HV)measurements.A layer by layer high-throughput investigation method was used to quantitatively study the grain growth kinetics and grain boundary evolution with different initial grain sizes,which could effectively save specimen and time costs.The grain nucleation and growth,as well as shrink and disappearance process throughΣ3 coincidence site lattice boundary migration with slightly lattice rotation during annealing were directly revealed.The layer by layer grain growth kinetics and calculated activation energy indicate that the thermal stability of nanograined top surface layer is relatively higher than that of nano-twined subsurface layer for the gradient CoCrNi MEA processed by ultrasonic surface rolling.Further analysis show that the grain boundary relaxation and dynamic recrystallization of the topmost nano-grains led to the decrease of grain boundary energy,thus improving their thermal stability.The present work provided theoretical basis for the application of CoCrNi MEA at high temperatures.Moreover,the high-throughput method on the investigation of grain stability by using gradient structure can be easily extended to other materials and it is of great significance for understanding the microstructural evolution of gradient materials.

关 键 词：Medium entropy alloy Grain growth Gradient materials Nanostructured materials Annealing High throughput 

分 类 号：TG139[一般工业技术—材料科学与工程]