原子尺度上相分离型合金熔体表征及非晶形成机制研究

The alloy with miscibility gap is layered due to the gravity during the solidification process, therefore, their application is limited. In recent years, several solidification techniques have been developed to make this kind of alloy own its special structure, then produce new purpose. The fact that amorphous alloy with liquid-liquid (L-L) phase segregation were prepared successfully provided a new research field for the design of porous materials. The researches on the alloy with miscibility gap are of great significance both for the scientific research and for engineering application. However, we lack the common understanding on this kind of alloy. In addition, for several alloy systems, the liquid phase miscibility gap happens in the undercooled liquid region, few studies focus on undercooled state and its following solidification behavior after phase segregation. In this project, taking Fe-Cu, Cu-Co alloy for example, the characteristics of structure, thermodynamics and dynamics parameters will be realized using molecular dynamics simulation. Our work focuses on the studies of L-L phase segregation behavior in undercooled regime. Based on these studies, the binary eutectic pairs criterion is used to design the alloy composition, the metallic glass with the characteristics of two different phases will be prepared; the investigation of the influence of negative enthalpy of mixing on the cluster evolution during rapid solidification process will be made to explore amorphous formation mechanism with L-L phase segregation alloy. The main purpose of the project is to provide theoretical basis and technical support for industrial application of phase segregation alloy, promote the development of research field of metallic glass.

液相分离型合金在通常凝固条件下会由于重力作用而分层，使其应用受到限制，而近年来发展的多种凝固工艺控制合金的微观组织使其具有新的用途，尤其是相分离型非晶的成功制备，为金属多孔材料设计提供新的研究方向。因此对相分离型合金研究具有工程实际意义和科学意义。目前缺乏对该类合金系共性的认识，一些合金的液相分离行为发生在过冷液相区，而对液相分离过程及随后凝固过程研究涉及较少。本课题以Fe-Cu、Cu-Co相分离型合金为例，采用分子动力学模拟，实现对相分离型合金熔体的结构、热力学及动力学表征；研究熔体在过冷液相区相分离行为；在此基础上采用多共晶成分叠加方法设计并制备相分离型非晶，探索共晶成分的负混合焓对合金熔体在快速凝固过程中团簇演变的影响，揭示相分离型非晶形成机制。通过以上研究为该类非晶合金的工业应用提供理论依据及技术支持，促进非晶合金领域的发展和深入。

相分离型合金在常规凝固条件下由于重力作用会出现偏析现象，导致其实际应用受到极大限制，近年来通过快速凝固等工艺可获得特殊性能的相分离合金，尤其是相分离非晶合金的成功制备为非晶合金的设计应用提供了新的研究方向。目前对相分离合金熔体、相分离非晶的形成机制以及结构和力学性能之间的关系还缺乏认识，对相分离型非晶合金的研究具有重要的工程实际意义和科学价值。.本课题以Fe-Cu典型的难混溶合金为例，在原子尺度合金对熔体结构、热力学、动力学性质进行表征，在此基础上探讨合金相分离机制。发现合金熔体具有正混合焓，同类原子间具有强烈的相互作用，相分离过程是上坡扩散过程，驱动力来自于合金系势能的降低。Fe50Cu50和Fe75Cu25合金熔体快速凝固过程中在过冷条件下分别受调幅分解和形核生长机制控制，随后在不同的冷速下形成不同的微观组织。只有富Fe相区能够形核，且晶体中出现孪晶，孪晶晶界处同类原子堆垛呈现出镜像对称。.对相分离Fe50Cu50非晶进行压缩试验，统计了不同相分离程度的非晶剪切变形区、短程有序结构及Voronoi体积随压缩变形的演变，探讨了非晶结构的不均匀性与塑性变形的相关性，发现随着相分离程度的增加，体系的自由体积降低，变形由宏观上的均匀变形向非均匀变形转变。提出团簇键长标准偏差的参数〖BLD〗_i，发现在热弛豫和非热压缩变形过程中，较长的热激活运动位移以及较大的剪切转变具有较大可能性发生在BLDi大的区域。利用铜模吸铸法制备出Zr65-xCu30Fex Al10（x=5和7.5 at.%）纳米尺度相分离非晶合金，并对其室温塑性进行探讨，发现纳米尺度分离相在非晶合金室温塑性变形的过程中诱导形成多重剪切带，特别是塑性变形后期在主剪切带周围形成多重剪切带，并构成稳定体系，从而提高非晶合金的室温塑性。