双态锆合金的微结构调控及强韧化机理研究

Security and economic of modern atomic engineering are closely related to the properties of structural component used in reactor. Zr-Nb alloys are the main material for manufacturing the key component, pressure tube. Therefore, it is important to improve the mechanical properties of Zr-Nb alloys. The duplex-zirconium alloy possesses high strength and high toughness simultaneously. However, the ω phase reduces the plasticity and the β enriched in Nb alloy element make the corrosion resistance worse. Therefore, it is worth removing the adverse factors in duplex microstructure via combining the formation process of duplex microstructure and manufacture processes of pressure tube, and obtaining a duplex-zirconium alloy which not only possesses high strength and toughness, but high applicability. Two kinds of typical Zr-Nb alloys are chosen as the object in this project. The duplex microstructure will be controlled via adjusting the processing parameters, such as deformation level, temperature, cooling rate, etc. The difference in the duplex microstructure and comprehensive mechanical properties between the alloys with different Nb content will be analyzed. Three dimensional atom probe technology will be introduced to study the partition of alloying elements. And then, a series of specimens with different strain were obtained via procedure tests, which was studied in detailed by using OM, SEM, TEM, XRD, EBSD, nano-indentation and in-situ tensile tests, to characterize the detailed microstructure, micro- deformation behaviour of each phase and co-deformation mechanism between the constitution phases, and the fracture behaviour, et al. This work will bring in an in-depth understanding on the mechanism of strengthening and toughening of duplex zirconium alloy, and come up with a theoretical and technical support for the microstructure controlling of high performance zirconium alloys.

现代核电工业的安全性和经济性与反应堆中结构件的性能紧密相关。因此，锆铌合金作为制造关键结构件-压力管的主要材料，提高其性能至关重要。双态结构锆铌合金兼具高强度和高韧性，然其组织中存在ω相和富Nb的β相，损害塑性和耐腐蚀性。因此将双态锆合金的制备工艺与锆合金压力管的制备工艺有效结合，消除不利组织因素，获得具有更高适用性和高强韧性的双态锆合金具有重要意义。本项目拟以两种典型锆铌合金为研究对象，通过调整工艺中变形、温度、冷速等参数，调控双态结构；对比不同制度下两种锆铌合金双态微结构和综合性能差异；利用3DAP技术分析合金元素在各相中的配分规律；采用过程研究方法获取不同应变试样，结合OM、SEM、TEM、XRD、EBSD、纳米压痕、原位拉伸等手段研究微观结构、各组成相微观变形行为及协调变形机理、以及断裂机制等科学问题。从而深入认识双态锆合金的强韧化机理，为高性能锆合金微结构调控提供理论和技术支持。

随着核工业地进一步发展，锆铌合金作为制造核反应堆关键结构件-压力管的核心材料之一，其性能直接影响着核反应堆的安全性和经济性，因此提高锆铌合金的性能至关重要。双态组织结构的锆铌合金兼具高强度和高韧性的特点，是一种有前景的结构材料。本项目主要针对以下七方面内容开展了研究：加工参数对双态锆合金组织与性能的影响、回火处理对空冷和水冷双态锆合金组织和性能的影响、初生alpha相含量对双态锆合金低温时效组织与性能的影响、低温时效对变形双态锆合金组织与性能的影响、原位变形研究、高温变形行为、Nb和Al含量对Zr-xNb-yAl合金影响。研究发现：在退火温度为750℃时，由于组织中生成了大量的硬脆相，导致合金塑性大幅度下降；850℃退火处理后合金获得最佳综合力学性能，强度和塑性分别可达到876MPa和31.3%。空冷和水冷获得的双态组织经300℃和400℃回火后，达到强度最高。空冷条件下初生α相体积分数的降低和α相中Nb固溶强化作用，两者综合导致相间协调变形能力降低。水冷条件下，各相强度较高导致协调变形能力更差。亚稳定β相的应变诱发马氏体转变主要发生在均匀变形阶段，裂纹优先萌生于次生板条状α相间，导致材料失稳；β相有利于各相协调变形，保证高的塑性。相比未变形态，变形可以使双态Zr-2.5Nb合金时效后的力学性能更加稳定。当Al含量达到5%时，Zr-2.5Nb-xAl合金中生成大量的金属间化合物，显著恶化塑性；随Nb含量增加，合金的强度和硬度提高，塑性降低，Nb含量为2.5 wt.%~4 wt.%时其静态韧性最高。通过本项目的研究，更加深入地认识了双态锆合金的强韧化机理，为高性能锆合金的开发和应用提供理论和技术支持。