Ti添加对U-5.7Nb-xTi合金相结构和力学性能的影响

Evolution of Phase and Mechanical Properties of Ti Alloyed U-5.7Nb-xTi Alloys

摘要:

由于拥有优秀的综合力学性能和抗腐蚀性能，淬火态U-5.7Nb (质量分数，%) 合金是核工业领域重要的结构材料。为了提升其较低的屈服强度，本文通过电弧熔炼制备了不同Ti含量的U-5.7Nb-xTi系列合金样品，并对其相组织结构和力学性能的演化规律进行了研究。随着Ti含量的上升，淬火态U-5.7Nb-xTi合金内首先会在α″相中形成γ0相，随后完全转化为γ0相，当Ti含量进一步上升至1.8% (质量分数) 时整个材料表现出高温奥氏体的体心立方相。将Ti等原子换算为平衡铌浓度Nbeq后，各相成分的边界与U-Nb合金十分吻合。与此同时，U-5.7Nb-xTi合金的硬度随着总合金含量的上升其硬度先下降后上升。通过分析U合金马氏体相变机制及金属材料固溶强化理论，发现U合金的相结构和力学行为分别由高温母相的屈服强度和马氏体相的孪晶能所决定。由于Ti和Nb的原子半径和体模量等物理参量非常相近，导致两者在对母相的固溶强化和对马氏体相孪晶能的贡献相当，进而使得Ti可以等原子替换Nb而对相结构和力学性能的影响较小。根据相同的物理机制，U-Nb-X三元合金（或更多元合金）可通过分析合金元素X的原子半径和体模量等物理参量，较为准确地预测不同X元素添加量对相结构和力学性能的影响，这为U-5.7Nb合金的进一步强化设计提供了理论依据和指导。

Abstract:

U-5.7Nb-xTi (wt. %) alloys with different Ti contents were fabricated by arc-melting. With the increasing of Ti contents, γ0 phase was first to appear in the α″ phase matrix, followed by its propagation. After completely transforming to γ0 phase at U-5.7Nb-1.2Ti, additional Ti alloying led to the formation of the equilibrium γ12 phase. After the Ti atom was equivalently converted to the equilibrium niobium concentration Nbeq, the boundary of each phase composition was very consistent with the U-Nb alloy. Meanwhile, the hardness of U-5.7Nb-xTi alloys were similar with those of U-Nb alloys with same total atomic contents. By analyzing the mechanism of transformation of the U-alloy and the theory of solid solution strengthening of the metal materials, the phase structure and mechanical behavior were considered to be closely related to the yield strength of the parent phase and twinning energies, respectively. Due to their similar physical parameters including atomic radii and bulk modulus, the solution strengthening effects of the parent phase and variation of the twinning energies led by Ti or Nb alloying were similar, which were responsible for the similarities of the phase structure and the mechanical properties in U-Nb-Ti and U-Nb alloys. According to the same physical mechanism, U-Nb-X ternary alloys (or multi-element alloys) can be more accurately predicted the phase structure and the mechanical properties by analyzing physical parameters such as the atomic radius and bulk modulus of alloying element X. These results and analyses provided theoretical basis and guidance for further strengthening design of U-5.7Nb alloy.