Research On Damage Behaviors Of Tungsten Materials Under High Heat/Particle Fluxes

Tungsten （W） materials are considered as most promising candidates forplasma-facing materials （PFMs） in future nuclear fusion devices. The damage behaviorsof tungsten materials under high heat/particle fluxes are of serious concerns not only tothe lifetime of PFMs, but also to the plasma operations and device safety. Therefore, thestudy of damage and erosion of tungsten materials under high heat/particle loads hasimportant scientific value and engineering significance. In this research, high heat flux（HHF） facility GLADIS and electron beam facility JUDITH1are used to investigatethe damage behaviors and underlying mechanisms of tungsten materials under fusionrelevant high heat flux and irradiation conditions.The recrystallization and grain growth behavior of rolled W under verticaldisplacement events （VDEs） heat loads has been studied. We observe that HHF cansignificantly increase the recrystallization temperature, reduce the time required forrecrystallization and refine the recrystallized grains. With increasing peak temperatures,the recrystallized grains grow bigger and the corresponding tensile strengths decrease.Furthermore, cyclic edge localized modes （ELMs） thermal shock tests have beenperformed on the recrystallized W. It turns out that the recrystallized W has bad thermalshock resistance. Electro-polishing and elevated base temperature （above theductile-brittle transition temperature） are found to be effective in promoting the thermalshock resistance and hence suppressing/retarding the surface cracking. Besides, theplastic deformation of recrystallized grains occurs under the cyclic thermal shocks.When the base temperature is elevated, the dynamic recrystallization （DRX） is observed,resulting in rough surface and refined DRX grains which lead to increased surfaceroughness and hardness.In addition, the melting behavior of W under VDE-like heat loads has beeninvestigated. Melt layer motion and redistribution results in severe erosion of thematerials. Bubble boiling in the melt layer induces melt layer ejection and result inporous re-solidified structure. For comparison, the melting tests of W-1wt%La₂O₃havebeen also carried out. The addition of La₂O₃particles notably affects the melt layermotion and suppress the bubble boiling. Detailed characteristics of melt layer structure are analyzed. Evaporation/boiling sources are indirectly studied with aid of vapordeposition/collection. Based on the experimental results, the possible underlyingmechanisms of bubble formation in W and bubble suppression in W-1wt%La₂O₃arediscussed and basic melting and boiling process under high heat loads of the twotungsten grades are tentatively drawn. Thereafter, the molten and re-solidified W isexposed to high heat flux helium neutral beams. With increasing peak temperature andhelium fluence, the damage depth of the molten surface increases, but is still lower thanthe non-molten surface. Blisters are observed on the molten surface, and evolve intoporous or coral-like structure with worsening irradiation conditions. The surfacemorphologies exhibit strong dependence on the re-solidified grain orientations.