Effects of alloying elements on hydrogen diffusion in γ-U alloys

In this study, we propose an effective strategy for selecting alloying elements to suppress hydrogen diffusion in γ-uranium (γ-U) based on the first-principles investigation of the Niobium (Nb) influences on hydrogen diffusion behavior. The simulation results show that the substitution of Nb in the body-centered cubic (bcc) lattice of γ-U significantly reduces the hydrogen diffusion rate, driven by two key factors: the thermodynamic stabilization of the γ-U bcc lattice and Nb’s strong hydrogen trapping effect. Diffusion energy pathway and electronic structure analyses reveal the presence of energy wells around Nb atoms, causing hydrogen to form cage-like diffusion pathways centered on Nb atoms, which effectively restricts long-range hydrogen diffusion in γ-U. Although Nb’s hydrogen trapping ability decreases at higher hydrogen concentrations, it still plays a crucial role in preventing the nucleation of UH3. Based on these findings, we propose a strategy for predicting hydrogen diffusion kinetics in a series of U-X (X = Ti, Tc, Nb, Mo, Re, Zr, In, Tl) alloys using first-principles static calculations, and establish a near-linear correlation between diffusion energy barriers, X-H bond lengths, and alloy formation energies. Our study underscores the importance of first-principles calculations in selecting suitable alloying elements to regulate hydrogen diffusion in uranium alloys, offering valuable insights with significant implications for engineering applications.

本研究基于第一性原理（first-principles）对铌（Niobium, Nb）影响γ-铀（γ-uranium, γ-U）中氢扩散行为的研究，提出了一种用于筛选合金元素以抑制γ-U中氢扩散的有效策略。模拟结果表明，Nb在γ-U体心立方（body-centered cubic, bcc）晶格中的置换占位可显著降低氢的扩散速率，该现象由两个关键因素驱动：一是γ-U bcc晶格的热力学稳定化作用，二是Nb对氢的强俘获效应。扩散能垒路径与电子结构分析显示，Nb原子周围存在能量阱，使得氢形成以Nb原子为中心的笼状扩散路径，有效限制了γ-U中氢的长程扩散。尽管在较高氢浓度下Nb的氢俘获能力会有所下降，但它仍在阻止UH3成核方面发挥关键作用。基于上述发现，本研究提出了一种通过第一性原理静态计算预测一系列U-X（X = Ti, Tc, Nb, Mo, Re, Zr, In, Tl）合金中氢扩散动力学的策略，并建立了扩散能垒、X-H键长与合金形成能之间的近似线性关联。本研究强调了第一性原理计算在筛选合适合金元素以调控铀合金中氢扩散方面的重要性，为相关工程应用提供了极具价值的理论参考。