摘要
利用电磁悬浮无容器处理技术实现了液态五元Zr_(57)Cu_(20)Al_(10)Ni_(8)Ti_(5)合金的深过冷与快速凝固,同时通过分子动力学模拟计算揭示了非晶形成的微观机制.实验发现,凝固组织具有明显的核-壳结构特征,核区为非晶相,壳区主要由ZrCu,Zr_(2)Cu和Zr_(8)Cu_(5)晶体相组成.非晶体积分数随合金过冷度的升高逐渐增大,当达到实验最大过冷度300 K(0.26TL)时,非晶体积分数增至81.3%.由此导出完全非晶凝固所需临界过冷度为334 K.TEM分析显示,过冷度增大并接近临界过冷度时,合金凝固组织中晶体相主要为Zr_(8)Cu_(5)相,而ZrCu和Zr_(2)Cu相的生长被抑制.在达到临界过冷度后,过冷液相的凝固路径由Zr_(8)Cu_(5)结晶生长转变为非晶凝固.此外,合金的晶体壳中存在少量的晶间非晶相,而非晶核中亦有微量的非晶间Zr_(8)Cu_(5)纳米晶团簇.模拟结果表明,晶间非晶相的形成主要源于近临界过冷度下偏析行为诱发的成分过冷,而非晶间纳米晶团簇的出现则主要归因于深过冷液相中的微观热起伏效应.
The substantial undercooling and rapid solidification of liquid quinary Zr_(57)Cu_(20)Al_(10)Ni_(8)Ti_(5)alloy are achieved by electromagnetic levitation(EML)technique.The amorphous solidification mechanism is revealed with molecular dynamics(MD)simulation.It is observed in EML experiment that the containerlessly solidified alloy is characterized by a core-shell structure,with mainly amorphous phase becoming the core and crystalline ZrCu,Zr_(2)Cu and Zr_(8)Cu_(5) phases forming the shell.The volume fraction of amorphous core structure increases with undercooling and attains a value up to 81.3%at the maximum experimental undercooling of 300 K,which indicates that the critical undercooling required for complete amorphous solidification is 334 K.TEM analyses show that the alloy microstructure is mainly composed of Zr_(8)Cu_(5) phase,whereas the ZrCu phase and Zr_(2)Cu phase are suppressed when liquid undercooling approaches this threshold.Once the critical undercooling is reached,amorphous solidification prevails over the crystallization of Zr_(8)Cu_(5) phase.In addition,a small quantity of amorphous phases are found in the crystalline shell and a little trace of Zr_(8)Cu_(5) nano-cluster is detected among the amorphous core.It is further verified by MD simulation that the formation of amorphous phase in the shell is caused by the microsegregation-induced solutal undercooling when liquid alloy attains the critical undercooling,while the nano-clusters within the core is mainly ascribed to the micro-thermal fluctuation effect inside highly undercooled liquid phase.
作者
徐山森
常健
翟斌
朱先念
魏炳波
Xu Shan-Sen;Chang Jian;Zhai Bin;Zhu Xian-Nian;Wei Bing-Bo(School of Physical Science and Technology,Northwestern Polytechnical University,Xi’an 710072,China)
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2023年第22期238-247,共10页
Acta Physica Sinica
基金
国家重点研发计划(批准号:2021YFA0716301)
国家自然科学基金(批准号:52088101,51771154)
陕西省重点研发计划(批准号:2023-YBGY-437)资助的课题。
关键词
电磁悬浮
非晶合金
深过冷
快速凝固
分子动力学模拟
electromagnetic levitation
amorphous alloy
highly undercooling
rapid solidification
molecular dynamics
