Dilute long period stacking/order(LPSO)-variant phases along the composition gradient in a Mg-Ho-Cu alloy

作     者：Kai Guan Daisuke Egusa Eiji Abe 

作者机构：Department of Materials Science and EngineeringThe University of TokyoTokyo 113-8656Japan Research Center for Structural MaterialsNational Institute for Materials ScienceTsukuba 305-0047Japan 

出 版 物：《Journal of Magnesium and Alloys》 (镁合金学报（英文）)

年 卷 期：2022年第10卷第6期

页      面：1573-1580页

核心收录：

学科分类：08[工学] 080502[工学-材料学] 0805[工学-材料科学与工程（可授工学、理学学位）] 

基　　金：supported by JSPS KAKENHI for Scientific Research on Innovative Areas “Materials Science of a Millefeuille Structure (Grant Nos. JP18H05475, JP18H05479)” “Nanotechnology Platform” of the MEXT, Japan supported by Grant-in-Aid for JSPS Fellows (JP19F19775) the Open Funds of the State Key Laboratory of Rare Earth Resource Utilization (RERU2020012) 

主　　题：Magnesium alloys Long period stacking/order(LPSO)phases Short-range order(SRO)clusters High-angle annular dark field scanning transmission electron microscopy(HAADF-STEM) 

摘      要：We have systematically investigated the microstructures of as-cast Mg_(97.49)Ho_(1.99)Cu_(0.43)Zr_(0.09)alloy by atomic resolution high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM), revealing the coexistence of 18R, 14H and 24R long period stacking/order(LPSO) phases with fully coherent interfaces along step-like composition gradient in a blocky intermetallic compound distributed at grain boundary. The short-range order(SRO) L1_(2)-type Cu_(6)Ho_(8)clusters embedded across AB’C’A-stacking fault layers are directly revealed at atomic scale. Importantly, the order degree of SRO clusters in the present dilute alloy is significant lower than previous 6M and 7M in-plane order reported in ternary Mg-TM(transition metal)-RE(rare earth) alloys, which can be well matched by 9M in-plane order. This directly demonstrates that SRO in-plane L1_(2)-type clusters can be expanded into more dilute composition regions bounded along the definite TM/RE ratio of 3/4. In addition, the estimated chemical compositions of solute enriched stacking fault(SESF) in all LPSO variants are almost identical with the ideal SESF composition of 9M in-plane order, regardless of the type of LPSO phases. The results further support the viewpoint that robust L1_(2)-type TM_(6)RE_(8)clusters play an important role in governing LPSO phase formation.