Vanadium boasts a relatively small atomic radius among numerous refractory alloying elements, yet its effects on the microstructure and mechanical behavior of refractory alloys remain enigmatic. In this work, a series of NbTiVZr high-entropy alloys (HEAs) with low density were formulated to explore the evolution of microstructures and mechanical properties with varying vanadium content. When the vanadium content was low, the matrix exhibited the single-phase body-centered cubic structure. Excessive vanadium contents (NbTiVZr, NbTiVZr) disrupted phase stability and tended to aggregate at grain boundaries, forming V-rich and Zr-rich phases. These precipitated phases pinned grain boundaries, impeding grain growth and resulting in both grain boundary strengthening and precipitation strengthening, albeit at the expense of grain boundary cohesion, ultimately leading to brittleness. However, these deleterious phases were redissolved, and fracture elongation increased more than 2 times after water quenching at 1200 °C. The microstructural changes induced by heat treatment were corroborated by alterations in grain boundary relaxation behavior, where the redissolution of precipitated phases after water quenching caused a shift of the grain boundary relaxation internal friction peak to a lower temperature and an increase in peak height. This study elucidates the intrinsic relationship between mechanical properties and microstructures with vanadium content in NbTiVZr alloys, offering insights for the design of TiV-based lightweight refractory HEAs with high strength and excellent ductility.

中文翻译：

---

V含量对NbTiVxZr高熵合金显微组织和拉伸性能的影响

在众多难熔合金元素中，钒的原子半径相对较小，但它对难熔合金的微观结构和机械性能的影响仍然是个谜。在这项工作中，配制了一系列低密度 NbTiVZr 高熵合金（HEA），以探索不同钒含量下微观结构和机械性能的演变。当钒含量较低时，基体呈现单相体心立方结构。过量的钒含量（NbTiVZr、NbTiVZr）破坏了相稳定性并倾向于在晶界处聚集，形成富V和富Zr相。这些析出相钉扎晶界，阻碍晶粒生长，导致晶界强化和沉淀强化，尽管是以牺牲晶界内聚力为代价，最终导致脆性。然而，这些有害相在1200℃水淬后重新溶解，断裂伸长率增加了2倍以上。热处理引起的微观结构变化通过晶界松弛行为的改变得到证实，其中水淬后析出相的再溶解导致晶界松弛内耗峰向较低温度移动并且峰高度增加。这项研究阐明了 NbTiVZr 合金中钒含量与力学性能和微观结构之间的内在关系，为设计具有高强度和优异延展性的 TiV 基轻质耐火 HEA 提供了见解。