面向等离子体Y2O3弥散强化钨基材料复合先驱粉原位制备及其烧结特性

Although as the most promising candidate of plasma facing materials, tungsten-based materials still have many disadvantages, such as difficult sintering densification, coarse grains, recrystallization embrittlement, irradiation damage and so on. Recently, it was found that the dispersion of Y2O3 second-phase particles in tungsten-based materials can significantly refine their grains, improve their mechanical property as well as enhance their ability of irradiation-proof. As a result, Y2O3 dispersion can effectively compensate for the disadvantages of tungsten-based materials mentioned above. However, the common doping techniques currently employed easily result in the concentration of Y2O3 particles at the tungsten grain boundaries, which dramatically depress their positive effect on the mechanical property of tungsten-based materials. Based on these backgrounds, it is proposed in present project that the W-Y2O3 composite powder precursor with controlled size and morphology can be in-situ fabricated using bottom-up liquid chemical method. Then the sintering behavior of this precursor will be studied in detail and accordingly the low-temperature rapid sintering technique is developed to prepare ultra-fine grained tungsten-based materials with Y2O3 homogenously distributed in both the tungsten grains and the grain boundaries, which will promote the application of tungsten-based materials in the plasma facing components. Moreover, in present project, the underlying mechanism of tungsten grains refinement and sintering densification promotion due to Y2O3 doping will be clarified and the influence mechanism of Y2O3 dispersion on the microstructure and mechanical property of tungsten-based materials will be understood. The intrinsic relationship between microstructure and mechanical property in the tungsten-based materials will also be summarized. All of these results will provide fundamental data and guideline to the researches on the sintering synthesis, microstructure control as well as performance optimization in the high-temperature alloys.

钨基材料作为未来面向等离子体最佳候选材料仍面临着烧结致密化困难、晶粒粗大、再结晶脆化和辐照损伤等问题。近期发现弥散分布的Y2O3第二相颗粒能够显著细化钨基材料晶粒，改善其力学性能和抗辐照能力，可有效弥补上述不足。不过目前常用的掺杂技术易导致Y2O3偏聚在钨晶界处，这大大削弱了Y2O3对钨合金性能的改善效果。鉴于此，本项目拟发展“自下而上”液相化学法和后续还原工艺原位制备尺寸和形貌均可控的W-Y2O3复合纳米先驱粉，并进一步研究该复合先驱粉的烧结特性，据此开发低温快速烧结技术制备出Y2O3在晶体内和晶界处弥散分布的超细晶钨基材料，推动其在面向等离子体部件中的应用。本项目还将澄清Y2O3细化晶粒和促进烧结致密化的内在作用机理，探明弥散分布的Y2O3对钨基材料微观组织及力学性能的影响机制，获得钨基材料微观组织和力学性能之间的内在关联性，为高温合金的烧结制备、组织调控及性能优化提供基础数据和指导。

钨基材料作为未来面向等离子体最佳候选材料仍面临着烧结致密化困难、晶粒粗大、再结晶脆化和辐照损伤等问题。弥散分布的Y2O3第二相颗粒能够显著细化钨基材料晶粒，改善其力学性能和抗辐照能力，可有效弥补上述不足。不过目前常用的掺杂技术易导致Y2O3在钨晶界处偏聚长大，这大大削弱了Y2O3对钨合金性能的改善效果。鉴于此，本项目通过引入超声处理和表面活性剂改进了传统的共沉淀湿化学法，并发展了新型的冷冻干燥法。通过这两种方法制备出了多种高质量W-Y2O3复合纳米粉体，其中钨的晶粒尺寸均细化至20nm以下，且尺寸均一、无双峰分布现象。Y2O3尺寸约为10~15nm，基本无团聚，均匀分布于复合粉体中。以我们制备的W-Y2O3复合粉体为先驱粉，在1600 ℃低温烧结4~6个小时就可以得到致密度98%以上、平均晶粒300~500nm的超细晶钨基合金，其中氧化物第二相颗粒得到明显细化，且均匀分布于钨晶粒内部和晶界处，最终烧结体的硬度超过了700 HV0.2。进一步考察了W晶体内和晶界处氧化物第二相颗粒与钨基体的界面精细结构。结果表明钨晶粒内部均匀分布的纳米氧化物（5~20 nm）颗粒为Y6WO12, 它们与钨基体呈现共格关系，可以通过有序化学强化的机理提高W的强度。在钨晶界处分布的氧化物颗粒仍为Y2O3，在这些Y2O3与W的界面处存在大约10 nm厚的W原子扩散层，但由于W原子扩散数量的限制并没有新相在该界面处形成。最后本项目还研究了W-Y2O3复合纳米粉体低温（1700 ℃以下）活化烧结致密化和晶粒生长动力学机制。发现纯W与W-Y2O3粉体在烧结过程中钨基体晶粒长大机制均为晶界扩散机制，但W-Y2O3 合金中晶粒长大激活能高于纯W，晶粒长大缓慢；进一步计算了W与Y2O3的界面能，结果表明Y2O3能够完全润湿W的表面，W原子会向相邻的Y2O3颗粒内部扩散，形成约10nm厚的扩散层，阻碍了W原子沿原晶界的扩散，进而抑制了W晶粒的长大。纯W与W-Y2O3粉体低温烧结致密化与晶粒生长密切相关，由于Y2O3添加后会降低烧结应力、减缓W晶粒生长以及阻碍W的表面扩散，这些因素最终抑制了W基体的低温烧结致密化。