Nanostructured Surface Layer On Tungsten By Smat And The Irradiation Damage Behavior Of Helium Ion Implanted In Tungsten And SIC

Plasma facing materials and components (PFM/PFCs) are not only the key to carry out the the future fusion reactor, but also one of the most important issues urgent to be solvedTungsten has been chosen as the plasma facing materials as armour materials of diverter, limiter and the first wall for ITER and DEMO due to its high melting point, high strength and thermal conductivity, low tritium retention property. However it’s high ductile to brittle transition temperature (DBTT), irradiation swelling and helium embrittlement which constrain its application. So it is of great significance and practical to improve the mechanical properties and decreased the DBTT of tungsten and tungsten alloys. Meanwhile, it has important significance to study the process of nucleation, growth and migration of helium bubbles and its structure exist in tungsten.In Chapter 3, a novel surface mechanical attrition treatment (SMAT) was introduced for fabricating a graded of nanostructured surface layer on W and WL10. The thickness of nanolayer is about 1μm in W and WL10, the mean grain size is about 11nm;φ1.5mm ZrO2 SMAT-ed W possesses significant improved bending strength, accompanied with DBTT value decrease 50℃; φ 1.5mm ZrO2 SMAT-ed WL10 possesses significant improved toughness (DBTT decrease 200℃), accompanied with bending strength decrease 120MPa. Microstructure results revealed that the nanostructure layer possess large amounts of stacking faults and dislocation cells. The nanomechanism in W and WL10 are similar to other metals (e.g Fe) with high stacking faults energy. In Chapter 4,the irradiation damage behavior of helium ion implanted tungsten was first studied with low energy(-keV), high-concentration of helium ion by SRIM. We have first reported the direct observation of solid helium bubbles in tungsten. The solid helium bubbles possess bcc structure, with lattice parameter about 0.447nm. The orientation relationship between the helium bubble and the W matrix is (110)He//(002)w, which is the same as the report by molecular dynamics (MD) simulation. Based on the MD simulation results and our TEM data, we proposed the possible growth process of solid helium bubbles.In Chapter 5, effects of helium implantation on silicon carbide (SiC) and graphite SMF-800were studied to reveal the possibility of SiC replacing graphite as the plasma facing materials. The surface morphology of SiC and graphite SMF-800 were studied before and after He+ implantation with 20 keV and 100keV at different temperatures and different fluences. The results indicated the excellent and better He+ radiation resistance of SiC than that of graphite SMF-800.