Y2Ti2O7纳米颗粒对含铝ODS钢微观结构和力学行为的作用机理

Oxide dispersion strengthened (ODS) steels with good creep strength and high radiation resistance are considered as one of the most important candidates for constructing the next-generation nuclear energy system. The addition of Al greatly improves the corrosion resistance of the ODS steels. However, this induces the formation of large Y-Al-O complex oxide particles in the matrix due to the reaction of Al with Y2O3 during the fabrication of the ODS steels, prevents Ti from reacting with Y2O3 to form the small and stable Y-Ti-O complex oxide nanoparticles (NPs), and deteriorates the mechanical properties of the ODS steels. Recently, by adding the Y2Ti2O7 NPs to substitute the conventional Y2O3 NPs, we successfully obtained Y2Ti2O7 NPs in the Al-alloyed ODS steels, which effectively inhibited the formation of the Y-Al-O particles and significantly improved the dispersion strengthening effect. In this project, we intend to further study the evolutions of microstructure and size of Y2Ti2O7 NPs during the fabrication of ODS steels, investigate the interface relationship between the oxide NPs and the matrix, elucidate the mechanisms for the nucleation and growth of Y2Ti2O7 NPs and their inhibition for the formation of Y-Al-O phase. In addition, the relationships of the microstructure of the matrix, the size and structure of the complex oxides with the mechanical properties of the ODS steels are systematically investigated, and the effects of Y2Ti2O7 NPs on the microstructure and mechanical behaviors of the Al-alloyed ODS steels are clarified. This project will establish the theoretical and experimental foundations for developing the high performance ODS steels.

氧化物弥散强化钢（ODS钢）具有优异的高温蠕变强度和抗辐照性能，是新一代核反应堆的重要候选结构材料。添加铝能够提高ODS钢的耐蚀性能，但铝在ODS钢制备过程中首先与钢中的Y2O3反应生成易长大的Y-Al-O复合氧化物，阻止了钛与Y2O3形成细小而稳定的Y-Ti-O纳米颗粒，导致强化效果降低。申请人前期通过添加纳米Y2Ti2O7以替代Y2O3，在含铝ODS钢中成功获得Y2Ti2O7纳米弥散相，有效抑制了Y-Al-O相产生，显著提高了弥散强化效果。本项目拟进一步研究ODS钢制备过程中Y2Ti2O7的结构和尺寸演变规律，确立氧化物与ODS钢基体的界面关系，揭示Y2Ti2O7纳米颗粒的形核和长大机制及其抑制Y-Al-O相产生的机理；研究ODS钢的基体微观结构、氧化物尺寸及结构与力学行为的相关性，阐明纳米Y2Ti2O7对ODS钢微观结构和力学行为的作用机理，为研发高强含铝ODS钢奠定理论和实验基础。

氧化物弥散强化钢（ODS钢）具有优异的高温蠕变强度和抗辐照性能，是新一代核反应堆的重要候选结构材料。添加铝能够提高ODS钢的耐蚀性能，但铝在ODS钢制备过程中首先与钢中的Y2O3反应生成易长大的Y-Al-O复合氧化物，阻止了Ti与Y2O3形成细小而稳定的Y-Ti-O纳米颗粒，导致强化效果降低。本项目采用氢等离子金属反应法制备出Y-Ti氢化物纳米颗粒，随后将其在900°C焙烧1h，成功制备出了高分散度的Y2Ti2O7纳米颗粒。由于焙烧温度和时间显著低于传统固相反应温度，因此颗粒尺寸仍然保持在纳米尺度（70 nm），并揭示了复合纳米氧化物的形成机理。将复合氧化物Y2Ti2O7纳米颗粒直接添加到基体中制备了模型合金粉末和含Al的ODS钢，发现经过96h球磨后Y2Ti2O7纳米颗粒没有发生分解或固溶于基体之中，而是尺寸逐渐减小并趋于发生非晶态转变。添加Y2O3纳米颗粒的ODS钢中的弥散相为YAlO3，平均尺寸为17.1nm，它与基体形成非共格界面。而新型添加Y2Ti2O7纳米颗粒的ODS钢中的弥散相为Y2Ti2O7，没有发现Y-Al-O存在，同时Y2Ti2O7平均颗粒尺寸仅为7～8nm。Y2Ti2O7与ODS钢基体保持半共格界面关系，[400]Y2Ti2O7 || [110]αFe 和[440]Y2Ti2O7 || [020]αFe。这是由于热成形过程中亚稳态Y2Ti2O7团簇优先在基体的(110)和(200)晶面形核并长大为fcc-Y2Ti2O7纳米颗粒，从而与基体保持良好的相界面关系。这些超细Y2Ti2O7纳米颗粒有效地提高了ODS钢的综合力学性能。随着Y2Ti2O7添加量从0.2wt%增加到0.6wt%，拉伸断裂强度从1238MPa增大到1296MPa，都远高于添加Y2O3的ODS钢（949MPa）。ODS钢强度差异主要取决于弥散相强化效果，与添加Y2O3的ODS钢相比，添加Y2Ti2O7的ODS钢中氧化物的数密度更大，氧化物间距大大减少，强化效果更大。同时，Y2Ti2O7和基体间的半共格界面也有效地阻止了氧化物附近微裂纹的形成，进一步提升了强化作用。最终阐明了添加纳米Y2Ti2O7对ODS钢微观结构和力学行为的作用机理，为研发高强含铝ODS钢奠定了理论和实验基础。