钽过冷液体等温晶化的原子层面机制  

Atomic-level mechanism for isothermal crystallization in supercooled liquid tantalum

作　　者：文大东 邓永和[1] 戴雄英[1] 吴安如[2] 田泽安[3] Wen Da-Dong;Deng Yong-He;Dai Xiong-Ying;Wu An-Ru;Tian Ze-An(chool of Computational Science&Electronics,Hunan Institute of Engineering,Xiangtan 411104,China;Hunan Provincial Key Laboratory of Vehicle Power and Transmission System,Hunan Institute of Engineering,Xiangtan 411104,China;School of Materials Science and Engineering,Hunan University,Changsha 410082,China)

机构地区：[1]湖南工程学院计算科学与电子学院,湘潭411104 [2]湖南工程学院,汽车动力与传动系统湖南省重点实验室,湘潭411104 [3]湖南大学材料科学与工程学院,长沙410082

出　　处：《物理学报》2020年第19期163-171,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51871096,11572124);湖南省自然科学基金(批准号:2018JJ3100,2018JJ4044);湖南省教育厅青年项目(批准号:19B122)资助的课题.

摘　　要：采用分子动力学模拟研究了钽(Ta)过冷液体的等温晶化过程,并用双体分布函数g(r)和最大标准团簇等方法表征和分析了体系的微结构演化特性.结果表明,Ta过冷液体的晶化过程敏感地依赖于过冷度,临界晶核形成孕育时间随过冷度的增加而减小.1800 K≤T≤1850 K,Ta过冷液体的晶化遵循Ostwald的分步规则:过冷液体中首先形成大量由Z12和Z14团簇铰链的中程序(即Z-MRO);随后Z-MRO长大并有序化为A15晶体相;最后体心立方(BCC)晶核在A15相内部快速长大成BCC晶体.而在1900 K≤T≤1950 K,过冷液体直接向A15相转变.A15相由最大尺寸的Z-MRO不断兼并周围小尺寸的Z-MRO并有序化形成.The morphology and physical properties of crystal as well as the glass-forming ability(GFA)of metals are closely related to the evolution pathway of atomic structures in the early stage of nucleation in supercooled liquids.Therefore,the study of the evolution of atomic structures in the isothermal crystallization process of supercooled liquids,is of great significance not only for predicting and accurately controlling the crystal nucleation and growth,but also for understanding the local atomic structural origin of the GFA.In the present work,the atomic-level mechanism for isothermal crystallization in the supercooled liquid tantalum is studied by molecular dynamics(MD)simulation.The microstructural evolution of metal Ta system is characterized and analyzed by using the potential energy per atom(PE),the pair distribution function(PDF)g(r),and the largest standard cluster(LSC).Two crystallization paths of Ta supercooled liquid can be observed during isothermal relaxations.For each pathway the incubation time of the formation critical nucleus increases with annealing temperature(T)rising.At 1800 K≤T≤1850 K,the crystallization of supercooled liquid Ta conforms to the Ostwald's step rule:first,Z12(i.e.icosahedron)and Z14(Kasper cluster with 14 coordination number)clusters in supercooled liquids are hinged into medium-range order(i.e.,Z-MRO);then the Z-MRO are merged and ordered into A15 crystal phase;finally,BCC crystal nucleus inside of the A15 phase grows rapidly into BCC single crystal at the cost of the atoms in A15 phase.While at 1900 K≤T≤1950 K,Ta supercooled liquid is directly transformed into A15 phase.The A15 crystal phase is mainly formed by the continuous merging of the largest Z-MRO with the small Z-MRO,which is similar to the picture of the classical nucleation theory(CNT).However,whether the phase transition from A15 to BCC will occur above 1900 K remains to be further confirmed by a longer-time MD simulation.Relative to the supercooled liquids of monoatomic metals with lower melting point,the g

关 键 词：过冷液体 晶化 原子结构 分子动力学模拟 

分 类 号：O614.513[理学—无机化学] TQ026.5[理学—化学]