Improvement in radiation resistance in refractory transition metals such as tungsten by radiation induced ductilization

显著改善难熔过渡金属（如钨）抗辐射脆化的方法包括应用辐射诱导的晶间沉淀、辐射诱导的马氏体转变和引入高密度的辐射诱导点缺陷汇。因此，研究了辐照前微观结构状态和辐照条件下这三个方面的有效发生。结果表明，在温度循环辐照条件下，由较低位错密度的细晶粒和细晶界弥散体组成的显微组织可发生辐射诱导的晶间析出。在较低的辐照温度和较高的辐照剂量下，具有高纯度基体的细晶粒可发生辐射诱导马氏体相变。引入非常高密度的槽可以包括微观结构条件的上述两个方面，前提是细晶粒的纯度高，位错密度低，并且可以在宽辐照条件下提供有益的效果。然而，这种情况是相当困难的，特别是钨在辐照前保持其他性能，包括足够的相对密度和韧性。在本研究中，采用先进的粉末冶金方法成功地引入了W-(0.3-0.7)%TiC的理想显微组织：例如，晶粒尺寸低至50-100nm，相对密度约为99%，断裂强度为2GPa。研究表明，W-(0.3-0.7)%TiC对快中子和He、N_2等高能离子的辐照具有很高的抗辐照性能。结果表明，该材料在辐射环境下作为导流剂和结构材料具有广阔的应用前景。

Methodologies for significant improvement in resistance to radiation embrittlement in refractory transition metals such as tungsten involve the applications of radiation-induced intergranular precipitation, radiation-induced martensitic transformation and introduction of a very high density of sinks for irradiation induced point defects. Therefore, pre-irradiation microstructural states and irradiation conditions for each of the three aspects to effectively occur have been examined. It is shown that radiation-induced intergranular precipitation can occur in microstructures comprising fine grains and fine grain-boundary dispersoids with a lower dislocation density under a temperature-cycle irradiation condition. Radiation-induced martensitic transformation can occur in microstructures of fine grains with a high purity matrix under irradiation at lower irradiation temperatures with higher doses. The introduction of a very high density of sinks can include the above two aspects of the microstructural conditions providing that the purity is high in the fine grains with a lower dislocation density, and can provide beneficial effects over wide irradiation conditions. This situation was, however, quite difficult especially for tungsten with maintaining other properties including sufficient relative density and toughness before irradiation. In this study, the desired microstructure has been successfully introduced for W-(0.3-0.7)%TiC by advanced powder metallurgical methods : e.g., the grain size is as low as 50-100nm with the relative density of approximately 99% and the fracture strength of 2GPa. It has been demonstrated so far that W-(0.3-0.7)%TiC exhibits very high resistance to irradiation by fast neutrons and high energy ions such as He and N_2. The results show that the material is very promising for the use as divertors and structural materials exposed to irradiation environments.