Irradiation effects of H/He neutral beam on different forged tungsten materials

Tungsten has been considered as the most promising plasma-facing materials (PFMs) for the future fusion reactor due to its excellent chemical and physical properties. In this work, different kinds of tungsten-based PFMs including pure W, W-K, and W-Y2O3 alloys were prepared via powder metallurgy. Then, high-energy rate forging was used for the plastic deformation to refine the grain size of the samples and increase their densities. To evaluate the service performance of these tungsten-based PFMs under edge plasma conditions, the deformed samples were exposed to high-energy hydrogen (H) neutral beam doped with 6 at% helium (He). Sequentially, edge-localized mode-like transient loadings (1 ms, 100 cycles) were carried out on the specimens with neutral beam pre-loading to study the impact of H/He pre-loading on the generation and propagation of cracks. The microstructural changes of the exposed surfaces were observed by scanning electron microscopy with the help of focused ion beam. The experimental results indicate that H/He neutral beam irradiation could induce obvious surface damages of the tested samples. For example, pinhole and coral-like nanostructures were formed on the surfaces of the exposed samples, as the surface temperatures were relatively high. The cracking thresholds of the W-Y2O3 samples with and without neutral beam pre-irradiations were both between 0.22 and 0.33 GW m(-2), while the cracking thresholds of pure W and W-K samples were less than 0.22 GW m(-2). This result indicates that the H/He neutral beam pre-loading has no significant impact on the cracking threshold. In addition, the crack pattern on the surface of the exposed samples closely depends on the grain boundary pattern.