As-cast microstructural features of a U-5.4Nb alloy, including average grain size, dendrite structure, inclusion evolution behavior, solute (Nb) distribution and micromechanical properties were investigated with respect to a diverse number of calculated cooling rates in this paper. Various solidification techniques, including suction casting, arc remelting and induction melting followed by argon cooling, were employed to obtain wide ranges of cooling rates between 90 K/s and 9.9 × 10⁵ K/s. Average grain sizes of suction cast samples decreased from 16.8 μm to 4.35 μm with increasing cooling rates. Similarly, inclusion evolution behavior was shown to refine in size with the increase of cooling rates. Fully developed dendrites inside the argon-cooled sample at a low cooling rate consisted of primary dendrite arms, secondary dendrite arms and tertiary dendrite arms that exhibited a fascinating dendrite structure with hexagonal symmetry. In addition, the segregation ratios of niobium decreased with decreasing cooling rates. Furthermore, the nanoindentation test indicated that the segregation of niobium had a significant influence on the mechanical properties of the dendrite arms and interdendritic regions. The elastic modulus and hardness for the primary dendrite arm, the secondary dendrite arm, and the interdendritic region were 61 GPa and 3.6 GPa, 62 GPa and 3.3 GPa, and 113 GPa and 6.5 GPa, respectively.

本文针对各种计算的冷却速率，研究了U-5.4Nb合金的铸态组织特征，包括平均晶粒尺寸，枝晶结构，夹杂物演化行为，溶质（Nb）分布和微机械性能。采用了各种凝固技术，包括吸铸，电弧重熔和感应熔化，然后再进行氩气冷却，以在90 K / s和9.9×10 ⁵之间获得宽范围的冷却速率。千/秒 随着冷却速率的提高，吸铸样品的平均晶粒尺寸从16.8μm降低至4.35μm。同样，随着冷却速率的增加，夹杂物的演化行为在尺寸上也有所改善。在氩气冷却的样品中，以较低的冷却速率充分发展的树枝状晶体由初级树枝状晶体臂，次级树枝状晶体臂和三级树枝状晶体臂组成，它们展现出具有六角对称性的迷人树枝状晶体结构。另外，随着冷却速度的降低，铌的偏析率降低。此外，纳米压痕测试表明，铌的偏析对枝晶臂和枝晶间区域的机械性能具有显着影响。初级枝晶臂，次级枝晶臂的弹性模量和硬度