物理学报2017，Vol.66Issue(1)：245-253,9.DOI:10.7498/aps.66.016101
冷速对液态金属Mg凝固过程中微观结构演变的影响
Simulation study of effect of cooling rate on evolution of microstructures during solidification of liquid Mg
摘要
Abstract
Magnesium metal and its alloys are widely used in industry,especially,as biodegradable materials are highly suitable for biomedical applications.Since macroscopic properties and service behaviors of materials are mainly determined by their microstructures,it is very important to in depth understand the melting structure of pure magnesium and its evolution process in solidification process.In this work,a molecular dynamic simulation studyis performed with embedded atom method potential at different cooling rates to investigate the rapid solidification process of liquid magnesium,and the microstructure evolution and phase transition mechanisms are systematically analyzed by using E-T curves,pair distribution function g(r),Honeycutt-Anderson (HA) bond-type index method,cluster-type index method (CTIM-3) and three-dimentional (3D) visualization method,respectively.It is found that the cooling rate plays an important role in the evolution of microstructures,especially;from HA bond index method,CTIM-3 and 3D visualization method,the microstructure details of crystalline or amorphous structures in the system are displayed quite clearly with temperature decreasing.Meanwhile,it can be easily found how some basic clusters interconnect to form a larger one in the system.For short,some local configurations under different conditions at four typical temperatures are also given to show the difference in microstructure on a relatively large scale.At a lower cooling rate of 1 × 1011 K/s,the evolution of metastable bcc structure is obviously consistent with the Ostwald's step rule in the system,meaning that the bcc structure is first formed preferentially and then dissociated largely,and eventually the stable crystalline structures are formed mainly with the predominant hcp structure and fcc structure,and coexisting along with remaining partial bcc structure.At a middle cooling rate of 1 × 1012 K/s,the crystallization process is slower,the bcc initially is formed at lower temperature,suggesting that the crystalline process is postponed,and the coexisting structures is still formed with the predominant hcp structure and fcc,bcc structures,but lacking in the larger grains,due to the competitions among the hcp,fcc and bcc structures.Finally,for a higher cooling rate of 1 × 1013 K/s,amorphous magnesium is formed with basic amorphous clusters characterized by 1551,1441 and 1431 bond types and there is not a predominant structure,although a small number of medium or long range orders come out.In addition,there surely exists a critical cooling rate for forming amorphous structures in a range of 1 × 1012-1 × 1013 K/s.From the evolution of bcc,it is also suggested that short range orders in super-cooling liquid give birth to bcc structure and the process can be avoided by simply speeding up the cooling rate to a critical one.关键词
液态金属Mg/快速凝固/微观结构演变/分子动力学模拟Key words
liquid metal Mg/rapid solidification process/microstructure evolution/molecular dynamics simulation引用本文复制引用
吴博强,刘海蓉,刘让苏,莫云飞,田泽安,梁永超,关绍康..冷速对液态金属Mg凝固过程中微观结构演变的影响[J].物理学报,2017,66(1):245-253,9.基金项目
Project supported by the National Natural Science Foundation of China (Grant No.51102090),the Program for New Century Excellent Talents in University,China (Grant No.NCET-12-0170) and the Natural Science Foundation of Hunan Province,China (Grant No.2016JJ2023).国家自然科学基金(批准号:51102090)、新世纪优秀人才支持计划(批准号:NCET-12-0170)、湖南省自然科学基金(批准号:2016JJ2023)资助的课题. （Grant No.51102090）
