空间模拟条件下锆基合金的非平衡凝固研究

Zr-based alloys are widely used in industry due to their excellent mechanical performance such as high specific strength and good corrosion resistance. Therefore, great efforts have been paid on the non-equilibrium solidification of these alloys. In this proposal, combined elimination of heterogeneous nucleation by high power laser irradiation with kinds of ground simulation technologies of space environment, such as drop tube, electromagnetic levitation, and electrostatic levitator, ternary liquid Zr-Ti-Cu and Zr-Ti-Ag alloys will be undercooled up to 0.2TL, and the rapid solidification process of such alloys will be realized with size from 0.02 to 20 mm. The project will focus on the nucleation feature, dendritic growth and glass transition characteristics. Meanwhile, the thermophysical properties of liquid Zr-based alloys, such as density, specific heat capacity, viscosity, and surface tension for alloy melts will be measured within a wide temperature range from high superheating to large undercooling. The microscopic structure variation of liquid alloy versus undercooling will be experimentally observed by synchrotron radiation and numerical simulated by molecular dynamics. Furthermore, the recalescence phenomenon during the rapid solidification of levitated liquid alloy droplets will also be studied by high-speed CCD camera in order to reveal the microstructure evolution. An effective routine to control the transition from crystal nucleation to amorphous formation will be found. In summary, this project is promising to build up the non-equilibrium solidification mechanism and explore the new ways to realize the glass transition of ternary Zr-based alloys.

锆合金因其高比强度和耐腐蚀等特性，具有重要的基础研究和工业应用价值，对其熔体非平衡凝固机制的物理阐释已成为一个重要的前沿课题。本项目以液固相变关系复杂的三元锆基合金为研究对象，采用落管、电磁悬浮和静电悬浮三种空间模拟技术，克服常规凝固器壁带来的异质晶核，获得0.2TL的过冷度，在微重力和无容器环境中实现合金液滴的快速凝固。研究其非平衡凝固过程的晶体形核、枝晶长大、共晶生长和非晶转变机制。系统测定从高过热到深过冷范围内的粘度和表面张力等热物理性质，实时记录悬浮液滴快速凝固过程动态影像，深入分析凝固组织的演变规律，结合同步辐射技术和分子动力学计算模拟，深入探索熔体微观结构与过冷度的内在关系。进而揭示热物理性质、微观机构和过冷度同Zr基合金熔体非晶转变的物理关联，并寻求有效的主动控制技术。项目的开展有望建立三元合金非平衡液固相变的相关理论模型，探索实现Zr基合金非晶转变的新途径。

本项目根据计划任务书达到了预期目标，在实际执行过程中进一步优化设计了合金成分，利用空间模拟技术研究了多个成分的Zr基三元和多元合金的非平衡凝固，着重探索了其凝固机理、非晶形成特征、热物理性质、燃烧和氧化特性、力学特性、耐腐蚀特性和电磁特性等物理化学性质。研究过程中综合考虑微重力、超高真空、无容器处理、电磁感应熔炼等超常规条件，克服常规凝固的不利因素，消除异质晶核，获得高达0.2TL的深过冷和10-6K/s超高冷速条件，进而实现深过冷条件下下的非晶转变，探索到一条利用空间模拟技术实现Zr 基合金熔体非晶转变的新途径。.研究了在仿空间环境下微尺寸合金液滴的非平衡快速凝固，深入探索合金熔体的晶体形核、初生相枝晶的快速生长同过冷能力、环境因素和液滴尺寸的内在联系，寻求有效的主动控制途径。实验测定了Cu-Zr-Ag三元合金的热扩散系数，发现热扩散系数均随温度的升高而呈现出不断增加的变化趋势，着Ag含量的增加而增大。研究了Ti45Cu35Zr10Ni5Sn5非晶条带在不同温度条件下的氧化和燃烧行为，发现燃点为940.8K，燃烧速度为1.04cm/s，氧化增重35.56%，氧化温度越高，氧扩散的速率越快，并发现Cu元素对合金的氧化具有一定的阻碍作用。研究了非晶条带Cu57.6Zr32.4Ce10合金的氧化行为，发现了氧化过程中，Cu向外迁移与O生产CuO颗粒，Zr与Ce向内迁移形成了层状的氧化产物结构。研究了Zr-Co-Al合金在NaCl、H2SO4和NaOH溶液中的耐腐蚀行为，发现Zr-Co-Al合金体系的钝化膜在1mol/L H2SO4溶液中最耐腐蚀。实验测定了Zr-Co-Al合金的热膨胀系数和热扩散系数，随着温度的增长和Al含量的增加而增长。在微重力条件下制备得到了Zr35Gd20Al23Ni22两相非晶合金，研究了其快速凝固过程的液相分离和非晶转变机制，发现随着过冷度和冷却速率的增大，合金中两非晶相塑性不断提高，硬度和杨氏模量呈现出先减小后增大的变化规律。相关研究成果在应用研究方面得到了初步探索。在这些研究的基础上，发表相关学术论文9篇，参加境内外学术会议5次，培养毕业硕士研究生2名，正在培养博士研究生3名，硕士研究生4名。