| Irradiation damage is the most characteristic and difficult issues in nuclear materials. It includes, typically, two typies of damage:one is self-radiation effect due to the radioactive solid-produced a particles such as Pu or tritium decayed He-3 and corresponding retention in its own lattice, the other is the external-radiation effects due to bombardment from neutron or other particles to the materials. The existence of these two effects will affect the performance and service life of materials proposed severe tests. This thesis is based on the above two irradiation environment to carry out experimental simulation study.Tritium is an element of considerable interest and has important technological applications, especially in the nuclear industry. However, helium will build up in metals as a result of tritium decay in metal tritides. When carrying out the experimental investigations, helium must be introduced into the solid artificially. Traditional ion implantation induces the critical lattice damage, while tritium decay and neutron irradiations are not suitable in the laboratories due to a long half-time or requiring special safety. This thesis brings a new method of helium introduction into metal which is called "ECR plasma-assisted magnetron sputtering deposition technology" This method behaves the advantages of helium introduction with uniform distribution and no extra displacement damage as well as of preparation with a dense, smooth, mirror-like metal film.The helium-containing Ti films were characterize systemically by using ion beam analysis (IBM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope (AFM), slow energy positron beam analysis (PAS) and thermal desorption spectroscopy (TDS). We found that the preferred crystal orientation of helium-doped Ti films was controllably varied from (002) to (100) orientation by increasing the bias voltage (i.e., ion bombardment current and energy). The dominant bombardment effect on the orientation was from the Ar ions of the anode sheath in the magnetron sputtering plasma region, and He bombardment also showed a slight influence on the orientation transformation at low trapped-helium content in the crystal. The helium incorporation process in this new method is mainly from the helium ion implantation in the ECR plasma sheath, which is different from the traditional magnetron sputtering method in which helium contribution in the film is recognized as the bombarding to the growing film of helium atom backscattered by the target and helium ions implanting in anode plasma sheath as well. The projectile energy of helium particles to the film is confined about 100 eV, near the sub-threshold-energy for displacement damage. So the lattice damage is rather lower, which is unlike the case of keV ion implantation. Further increasing helium content will induce great lattice expansion, Bragg peak broadening, the grain refinement and disorder enhancement. The characteristics of relative cell parameters and peak broadening versus helium content are more closed to those of tritium decay compared to traditional magnetron sputtering method.Using the new ECR plasma-assisted magnetron sputtering deposition system (PMS), the argon plasma bombardment energy and Ti film deposition rate can be controlled separately, with the substrate bias voltage under feedback control. Results from SEM and AFM show that the properties of Ti films prepared by ECR-PMS are greatly improved compared with conventional sputtering, such as dense morphology, smooth surface, etc..Doppler broadening of PAS analysis also reveals that the Ti films have fewer vacancy defects compared with films prepared by the conventional magnetron.Combining all the above-mentioned analysis results, it is shown that the state of helium atom in the film by ECR-PAS method is more like that in tritides and it may be used to simulate the accumulation of helium in tritides, and avoid the long term for decaying.Ti3SiC2 MAX phase materials have been considered as the most potential candidate for the structural materials of the first wall/blanket for fusion reactor. The second part in this thesis is to investigate radiation damage mechanism of the Ti3SiC2 bulk materials. The dissertation concentrated mainly on the microstructure analysis of Ti3SiC2 by incident X-ray diffracttion (GIXRD) using aynchrotron radiation. The surface morphology of the sample was analyzed by SEM and AFM.The Ti3SiC2 was irradiated with high fluence 2 MeV I2+ ions. The shift and broadening of the observed diffraction peaks are due to a range of defects ranging from micron scale in size. PAS analysis shows that the irradiated samples have more vacancy-type defects compared to the unirradiated sample, and a significant increase of the defects occurs at in the surface layer after high dose irradiation. Combining this analysis with both SEM and XRD reveals that a TiC nanocrystalline phase was formed under the high dose irradiation. Post irradiation annealing to temperatures of 500-800?results in crystal regrowth of Ti3SiC2 and TiC phase.Next, the Ti3SiC2 was irradiated by three self-ions (Ti?Si and C). These experiments reveal that, all of the samples become a two phase material with coexisting Ti3SiC2 and TiC components under high dose irradiation. It is noteworthy that, C ion irradiation damage at a highest doses, MAX-phase remained crystallinity, although Ti3SiC2 phase occurred decomposition. When the samples irradiated by Ti and Si ions at a relative higher dose, the crystal takes on a more serious disorder. The reason of the Ti3SiC2 phase decomposition and MAX phase disorder may be related to irradiation ion species, irradiation dose and ion damage rate (dpa/s) and so on.Analyzing the helium behavior of Ti3SiC2 sample by PAS, the results show that low energy and high-flux helium ions implantation into the sample surface, it could be accumulated a high helium concentration at top surface in a short time, and causing the surface microstructure changes, such as helium bubble aggregation, growth and migration etc. The results of synchrotron radiation GIXRD analysis reveal that the sample surface layer will show a more serious amorphous phenomenon under the He, Si ions co-irradiation compared with the case of sample irradiated by iodide ion at a highest dose. |
PDF Full Text Request