一种不稳定的共晶生长方式:倾斜共晶生长的研究进展

An Unstable Eutectic Growth Mode:Research Progress of Tilt Eutectic Growth

共晶组织的制备过程是指在一定溶质浓度的合金熔体中,在冷却阶段同时析出紧密相邻的两种或多种不同固相的过程。这些析出的固相如果能规则地分布于基体中,就能制备出具有多种特殊性能的共晶组织材料。共晶组织材料作为耐高温部件材料在航空航天以及核工业等领域具有重要的应用价值。有些科学家在共晶理论的基础上提出了应用定向凝固法制备规则的多孔金属结构的新工艺,而多孔金属独特的力学性能和热学性能预示着它具有广阔的应用前景。制备共晶组织材料的关键是在给定的制备条件下有效地控制共晶的凝固过程。共晶凝固过程中存在两个至关重要的问题:一是共晶凝固过程的动力学;二是共晶固-液界面、固-固界面的形成与演化。这两者决定着最终产品材料的品质与性能,需要进行大量深入的研究。两者的相互影响构成了一个不可分割的非线性动力系统。共晶生长理论的研究重点是探究二者在共晶生长中的耦合行为。因此,共晶生长的预期理论研究成果将使人们对微观组织的形成与界面的演化有更深刻的理解。基于这些理解,可以更好地控制凝固过程,使界面产生需要的微观结构,从而获得力学性能更加优良的产品。理论上而言,定向凝固实验中层片状共晶的生长方向和温度梯度方向应一致。但是在一定的生长条件下,共晶固-液界面会沿着垂直于牵拉速度的方向移动,导致固-固界面与牵拉速度方向呈一定的倾角,从而形成共晶生长的另一种模式,即倾斜共晶生长。对倾斜共晶生长的研究有助于提高共晶材料的性能,而且倾斜共晶生长的相关研究工作也是共晶凝固理论的重要组成部分,对理解和解决工业生产中共晶材料制备的诸多难题具有重要的指导意义。目前,研究者对层片状倾斜共晶生长的影响因素和形貌开展了大量的理论研究和实验报道。本文从倾斜共晶生长的发展和定向凝固技术方面,对层状倾斜共晶生长的研究进展与方法进行阐述,主要包括倾斜共晶生长中各种参数以及各向异性对倾斜共晶生长形貌的影响规律,同时对该领域的未来研究方向进行展望。

The preparation process of eutectic structure refers to the process of precipitating two or more different solid phases closely adjacent to each other during cooling in the alloy melt with a certain concentration of solute.If the two closely adjacent two or many different solid phase processes are formed,at the same time,the precipitated solid can be distributed regularly in the matrix,a variety of eutectic material with special properties can be prepared.And eutectic structure materials are widely used in aerospace and nuclear industry.On the basis of eutectic theory,some scientists have proposed a new process of preparing regular porous metal structure by directional solidification method,and the unique mechanical and thermal properties of porous metal indicate that it has a broad application prospect.The essential problem in the preparation of eutectic microstructure is that how to effectively control the solidification process of eutectic under given preparation conditions.Dynamics of eutectic solidification process,formation and evolution of eutectic solid-liquid interface and solid-solid in-terface are two basic problems in eutectic solidification,they constitutes an indivisible nonlinear dynamical system.Meanwhile,they determine the quality and properties of final product materials,so they are needed to be studied deeply.The key factor of eutectic growth theory is to explore the coupling behavior of the two in eutectic growth.Therefore,the theoretical results of eutectic growth will enable people to understand the formation of microstructures and the evolution of interfaces.So,we can better control the solidification process and obtain better mechanical properties of the product.It has been known for a long time that,the directional solidification of eutectic alloys at near eutectic compositions,the theoretical orientation of lamellar eutectic growth is consistent with that of temperature gradient.But there are certain growth conditions,the eutectic solid-liquid interface will move along in the vertical direction of the pulling speed,so it will result in a certain angle of inclination between the solid-solid interface and the traction velocity,Thus,another mode of eutectic growth is produced:inclined eutectic growth.The theory of eutectic solidification can be further improved,the properties of eutectic materials can be improved and the problem of preparing eutectic materials in industrial production can be solved,if we study the tilt growth of eutectic.A large number of theoretical and experimental studies have been carried out on the influence factors and morphology of the layered eutectic tilt growth.In this paper,the research progress and methods of stratified eutectic slant growth from the development of oblique eutectic growth and orientation solidification technology are described.The influence of various parameters and anisotropic on the morphology of tilt eutectic growth is summarized.We point out some questions in current researches,and propose the new perspectives for future research.