新型ZrTiAlV合金马氏体相变诱发亚稳相形成规律研究

Zr-based alloys are of significant application value in aerospace, nuclear industry and chemical industry due to their excellent physical and chemical properties, such as high strength, good anti-irradiation, corrosion resistance, oxidation resistance and small neutron absorption area. The martensitic transformation and formation of martensite-induced metastable phases of Zr-based alloys have important influence on its mechanical properties. In our previous study, it was found that the yield strength and tensile strength of a ZrTiAlV alloy increase 29% and 23%, respectively, comparing to the forged alloy after martensitic transformation and formation of metastable phases by proper aging treatment, which indicates strengthening effect is remarkable. Consequently, it has important significance for the strengthening and toughening design of Zr-based alloys to systematically study the martensitic transformation and formation rule of it induced metastable phases. In this project, the electron concentration of system, bond order between atoms and orbital energy level of the elements in the Zr-based alloys are going to be altered by changing the composition of neutral elements, alpha-stabilizing elements and beta-stabilizing elements of the alloys so as to reveal the phase selection process during martensitic transformation and its influencing factors, also to understand the physical basis of martensitic transformation and the formation of it induced metastable phases. The thermodynamic and kinetic mechanism of martensitic transformation and the formation of metastable phases from solid state decomposition of martensite is going to be elucidated. Moreover, the influence law of martensitic transformation and the structure, morphology and stability of martensite induced metastable phases on mechanical properties of Zr-based alloys is going to be explored. The technical approach to strengthening Zr-based alloys by influencing the process of martensitic transformation and formation of the metastable phases will be put forward.

锆合金具有高强度、中子吸收截面小、抗辐照和耐腐蚀等特点，在空间、化工和核工业中具有重要应用价值。锆合金中产生的马氏体相变及其诱发的亚稳相形成规律对其力学性能具有重要的影响。申请人前期研究发现ZrTiAlV合金发生马氏体相变后经过适当时效处理产生亚稳相使其屈服强度和抗拉强度比锻造态提高29%和23%，强化效果显著，因此关于锆合金的马氏体相变及其诱发的亚稳相形成规律的系统研究对于锆合金的强韧化设计具有重要的意义。本课题拟通过调控合金体系中的中性元素和alpha相、beta相稳定元素，改变体系价电子浓度，原子键级以及元素轨道能级揭示马氏体相变相选择过程和影响因素，查明马氏体相变及其诱发亚稳相形成的物理基础。阐明马氏体相变和亚稳相形成的热力学和动力学机制。探讨马氏体相变及诱发亚稳相的结构、形貌和稳定性对锆合金力学性能的影响规律。提出通过调控马氏体相变及亚稳相形成强化锆合金性能的技术思路。

锆合金具有高强度、中子吸收截面小、抗辐照和耐腐蚀等特点，在空间、化工和核工业中具有重要应用价值。锆合金中产生的马氏体相变及其诱发的亚稳相形成规律对其力学性能具有重要的影响。本项目制备了不同成分的锆合金，以51Zr-40Ti-5Al-4V（51Zr）合金为例，原始态的合金中含有α相、β相以及α″相。通过淬火处理，51Zr合金由马氏体α″相和β相两相组成。随着淬火温度的升高，α″马氏体相的衍射峰强度减弱，而β相衍射峰的强度逐渐增强，说明合金中β相在淬火过程中被保留下来的数量逐渐增多。合金锻造态的微观组织具有大小比较均匀的β晶粒，同时在β相基体中存在层片状α相和针状α″马氏体相。700℃固溶后在大晶粒交界处出现了一些晶粒尺寸大小约为30μm左右的小晶粒，出现了再结晶的现象，同时在β相基体中析出了一些细小的针状α″马氏体相。另外添加Fe元素，DSC曲线显示合金的马氏体相变温度受Fe含量影响很大，马氏体相变结束温度随Fe含量升高而降低，随着铁含量由0%升高到2.5%（wt.%），马氏体相变结束温度从843℃降低到762℃。马氏体相变开始温度随着Fe含量升高先降低后保持在620℃左右。XRD分析表明当Fe含量低于等于1.5wt.%时，合金主要由α'和β相组成，当Fe含量达到2.0wt.%或更大时，合金主要由β相组成。随着Fe含量的增加，表示β相的峰变得更宽更强，直到Fe含量达到2.0wt.%，表示α'相的峰完全消失。TEM图像以及其对应的SAED图分析表明：α'相晶粒随着Fe含量增加逐渐变细。铁含量为0.5wt.%的合金综合力学性能最优。本项目研究了锆合金马氏体相变的影响规律及其诱发的亚稳相形成规律，对锆合金开发和服役具有重要意义。