Abstract Dense U3Si2 pellets with controlled grain structure and enhanced thermal-mechanical and oxidation properties are synthesized with spark plasma sintering (SPS). Microstructure and phase composition of the SPS densified pellets are characterized systematically using SEM, EDS, and XRD. Thermal-mechanical properties and oxidation behavior of the sintered silicide fuel pellets are analyzed by laser flash, indentation, and dynamic thermogravimetric analysis. Dense U3Si2 pellets are consolidated by combining high energy ball milling and rapid sintering by SPS, and the microstructure structures are controlled from micron-sized (∼5.7 μm grain size) for conventional silicide to a nanocrystalline matrix with an average grain size of ∼280 nm. A dominant phase of distorted U3Si2 was identified with lattice expansion due to residual thermal stress upon SPS consolidation and rapid cooling processes. Both micron-sized and nano-sized pellets show exceptional thermal transport properties, consistent with monolithic silicides reported in literature. The SPS-densified pellets possess simultaneously high hardness and fracture toughness. The SPS-densified silicide pellets also demonstrate exceptional oxidation performance with extended onset oxidation temperature above 500 °C and reduced oxidation kinetics, particularly for nano-sized pellets. A strong strain effect was proposed in which compressive stress in nano-sized pellets enhances the oxidation resistance of silicide fuels, as evidenced by the degradation of oxidation performance upon strain relaxation by isothermal annealing. The correlation among the sintering process – microstructure control – physical properties and fuel behavior is established. A new concept of strain engineering is proposed further properties optimization, enabling the development of potential oxidation and corrosion-resistant silicides with extended performance, the key technological challenge of U3Si2 as the leading concept of accident tolerant fuels.

中文翻译：

---

火花等离子体烧结 (SPS) 致密 U3Si2 球团：微观结构控制和增强的机械和氧化性能

摘要 通过放电等离子烧结 (SPS) 合成了具有可控晶粒结构和增强的热机械和氧化性能的致密 U3Si2 球团。使用 SEM、EDS 和 XRD 系统地表征 SPS 致密颗粒的微观结构和相组成。通过激光闪光、压痕和动态热重分析来分析烧结硅化物燃料芯块的热机械性能和氧化行为。通过结合高能球磨和 SPS 快速烧结，将致密的 U3Si2 球团固结，微观结构控制从常规硅化物的微米级（~5.7 μm 晶粒尺寸）到平均晶粒尺寸为~280 nm 的纳米晶基体. 由于 SPS 固结和快速冷却过程中的残余热应力，扭曲的 U3Si2 的主要相被识别为晶格膨胀。微米尺寸和纳米尺寸的颗粒都显示出优异的热传输特性，与文献中报道的整体硅化物一致。SPS 致密颗粒同时具有高硬度和断裂韧性。SPS 致密的硅化物颗粒还表现出卓越的氧化性能，将起始氧化温度延长至 500 °C 以上并降低氧化动力学，尤其是对于纳米尺寸的颗粒。提出了一种强应变效应，其中纳米颗粒中的压应力增强了硅化物燃料的抗氧化性，正如等温退火应变松弛时氧化性能的下降所证明的那样。建立了烧结过程-微观结构控制-物理特性和燃料行为之间的相关性。提出了一种新的应变工程概念，以进一步优化性能，从而开发具有扩展性能的潜在氧化和耐腐蚀硅化物，这是 U3Si2 作为容灾燃料的领先概念的关键技术挑战。