Dense uranium mononitride (UN) pellets with controlled microstructures and tailored grain size from large-grained to a few microns are synthesized by spark plasma sintering (SPS) combined with high energy ball milling. The impacts of the sintering conditions on fuel microstructure, grain size, physical density, and phase behavior are systematically investigated, and the thermal-mechanical properties and oxidation behavior of the SPS densified UN pellets are characterized. Higher sintering temperatures and longer ball milling durations and thus finer starting UN powders promote sintering and densification, and dense UN pellets above 95% theoretical density can be achieved by SPS at 1873 K for 10 min. UN phase purity is maintained in the SPS-densified pellets sintered at a lower temperature and short duration. A phase heterogeneity with secondary UO₂ or uranium sesquinitride (U₂N₃) occurs for the UN pellets sintered at higher temperatures using finer UN powders. The hardness and fracture toughness of the SPS-densified UN pellets increase with smaller grain sizes and higher densities to 7.9 GPa and 3.5 MPa m^1/2, respectively. Both small (1–2 μm) and large grain-sized (30–50 µm) UN pellets exhibit good thermal conductivity. Dynamic oxidation testing by a thermogravimetric analyzer in air shows that the onset temperature for oxidation varies with microstructure and phase heterogeneity of the SPS densified UN pellets. Particularly, the smaller-grained (micron-sized) UN pellets containing uranium oxides and U₂N₃ display lower weight gain and significantly-reduced oxidation kinetics, and full oxidation completes at a temperature above 1173 K when tested with a ramp rate of 10 K/min.

通过放电等离子烧结 (SPS) 结合高能球磨合成了具有受控微观结构和从大晶粒到几微米的定制晶粒尺寸的致密一氮化铀 (UN) 球团。系统研究了烧结条件对燃料微观结构、晶粒尺寸、物理密度和相行为的影响，并表征了 SPS 致密 UN 芯块的热机械性能和氧化行为。更高的烧结温度和更长的球磨持续时间以及更细的起始 UN 粉末促进了烧结和致密化，并且通过 SPS 在 1873 K 下 10 分钟可以实现高于 95% 理论密度的致密 UN 颗粒。在较低温度和短时间烧结的 SPS 致密颗粒中保持了 UN 相纯度。具有二次 UO 的相异质性₂或铀倍半氮化物 (U ₂ N ₃ ) 出现在使用更细的 UN 粉末在更高温度下烧结的 UN 颗粒。SPS 致密的 UN 球团的硬度和断裂韧性随着更小的晶粒尺寸和更高的密度而增加，分别达到 7.9 GPa 和 3.5 MPa m ^1/2。小 (1–2 µm) 和大颗粒 (30–50 µm) UN 颗粒均具有良好的导热性。空气中热重分析仪的动态氧化测试表明，氧化的起始温度随 SPS 致密 UN 颗粒的微观结构和相异质性而变化。特别是，含有氧化铀和 U ₂ N ₃的较小颗粒（微米级）UN 颗粒 显示出较低的增重和显着降低的氧化动力学，当以 10 K/min 的升温速率进行测试时，完全氧化在 1173 K 以上的温度下完成。