超高静磁场下凝固制备均质难混溶合金材料的基础研究

Homogeneous Immiscible alloy is one of the most important functional and structural materials due to their excellent electric, magnetic, mechanical and electrochemistry properties. However, there exists severe specialty of liquid to liquid separation, even in microgravity surrounding, the macro segregation cannot be damped, and it is very hard to study the specialty of equilibrium solidification, the preparation process of immiscible alloy is one of most difficult challenges.In this project, refer to the immiscible alloys with different magnetism properties such as Zn-Bi, Cu-Pb or Cu-Co etc., we suggest that, with the help of using huge magnetism energy, magnetic force, Lorenz force induced by 20-35T Super High Static Magnetic Field(SHSMF), the thermodynamics and kinetics of the nucleation and growth in solidifying immiscible alloy will be influenced, the gravity segregation and agglomoration of second phase droplets due to Stokes sediment, Oswalt curing and Marangoni convection can be damped. By using experimental and mathematic modeling methods, we will study the specialty of equilibrium solidification in immiscible alloy in SHSMF, discuss the orientation principle of second droplet and base crystal, reveal the evolvement of Solid-Liquid and Liquid-Liquid interface, and finally obtain homogenous immiscible alloy with the second phase in the size of nano or micro meters distributed evenly in solidified alloy, then measure its electric, magnetic, deforming and mechanic properties carefully and discuss the possible mechanism due to effect of SHSMF, and based which, the Phenomenological model between properties and micro structure will be set up, and a new field of preparing advanced materials with excellent performance by solidifying way in SHSMF will be explored out.

均质难混溶合金的电/磁/力学和电化学性能优异，是极为重要的功能结构材料之一。但凝固时存在严重的液液分离现象，即使用微重力等极端条件也很难调控其凝固过程，其平衡凝固特性很难展开研究，也是材料制备领域的一大难题。本项目提出，针对Zn-Bi、Cu-Pb或Cu-Co等不同磁特性难混溶合金体系，利用20-35T超高静磁场这一极端环境中巨大的磁场能、磁力、洛伦兹力效应，影响难混溶合金凝固中形核、长大过程的热力学和动力学，抑制Stokes沉降、Oswalt熟化、Marangoni对流引起的凝并和偏析。采用实验和数值模拟手段，考察超高静磁场下该类合金的平衡凝固特性，探究第二相熔滴、晶体的取向生长机制，揭示固液界面、液液界面的演化机制，最终制备出第二相呈微米甚至纳米级分布的均质难混溶合金，并对其电、磁、力学性能进行精细表征和机理分析，建立微结构-性能之间的唯像模型，开辟超高静磁场下凝固制备高性能材料的新领域

均质难混溶合金的电/磁/力学和电化学性能优异，是极为重要的功能结构材料之一。但凝固时存在严重的液液分离现象，是材料制备领域的一大难题。针对Zn-Bi、Cu-Co、Al-Bi、Bi-Mn等难混溶合金以及Al-Cu模型合金，本项目采用0-30T超高静磁场制备高性能的难混溶合金材料。发现AlCu互扩散系数（DAlCu）在973 K时为5.2×10-9 m2s-1，在1023K时为7.2×10-9 m2s-1。22 T磁场下两者分别降低为2.8×10-9 m2s-1和3.4×10-9 m2s-1，该数值能够和微重力环境下测得的数值相媲美。定向凝固研究结果表明，随着生长速度的增加，固-液界面由平面状向胞状再向枝晶状转变。这主要归因于界面不稳定性和对流不稳定性的共同作用。强磁场对凝固组织的影响主要是通过控制熔体对流来影响界面不稳定性。同时，本项目给出了难混溶合金凝固析出相纤维颈断的预测判据。对于Zn-Bi合金，超高静磁场抑制Bi液滴的Stokes运动和Marangoni运动，降低其尺寸，消除偏析，复合高过热度降低合金电阻率。此外，发现30T下，Bi-Mn合金组织的取向及分布不同。慢冷速时α-BiMn相交替分层出现，快冷速时呈现沿着磁场方向高度取向。还发现，22T梯度场更有利于获得均质难混溶合金材料。摩擦磨损试验结果表明，21T匀强磁场试样比0T摩擦系数降低42%。此外，合金熔体表观动力粘度的测试结果表明：随着磁感应强度的增加，熔体粘度以二次函数的形式增加，10T比0T提高约40倍。Cu-Co合金的性能测试结果表明，10T下样品的抗拉强度、屈服强度、均匀延伸率和饱和磁化强度比0T分别提高29 %、26 %、39 %和14.7%。本项目发现了磁场下成分过冷降低诱导组织粗化的新机制，形成了强磁场下MHD效应稳定固液界面和梯度强磁场悬浮制备均质难混溶合金的新思路。本项目的研究对材料制备、冶金、物理、流体力学学科的发展提供了丰富的理论和技术支持。本项目执行期间，在合肥国家强磁场实验中心开展了近300个小时的高场（20-30T）研究，在法国LNCMI实验室开展近100小时高场(18-30T)研究，为大科学装置未来在金属材料制备与应用提供了重要借鉴。本项目在JAC、Science、PRB和JFM等期刊发表SCI/EI论文64篇，申报发明专利8项，授权2项、获奖3项，培养博硕士研究生40余人。