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

显著提高钨等难熔过渡金属的抗辐射脆性的方法包括应用辐射诱导的晶间析出、辐射诱导的马氏体相变和引入非常高密度的汇来处理辐射诱导的点缺陷。因此，对辐照前的微结构状态和有效发生这三个方面的辐照条件进行了研究。结果表明，在温度循环辐照条件下，由细晶和细晶-晶界弥散相组成的显微组织中可产生位错密度较低的辐照诱导晶间析出。在较低的辐照温度和较高的辐照剂量下，具有高纯基体的细晶组织可以发生辐照诱发马氏体相变。在具有较低位错密度的细晶中纯度高的情况下，引入非常高密度的槽可以包括上述两个方面的微结构条件，并且可以在广泛的照射条件下提供有利的效果。然而，这种情况是相当困难的，特别是对于钨来说，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，用先进的粉末冶金方法成功地制备出了W-(0.3-0.7)%TiC合金所需的显微组织：晶粒尺寸为50-100 nm，相对密度约为99%，断裂强度为2 Gpa。到目前为止，W-(0.3-0.7)%TiC材料具有很高的抗快中子和高能离子(如He和N_2)辐照的能力。结果表明，该材料在偏滤器和辐射环境中的结构材料方面具有很好的应用前景。

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.