Study Of Effects On Helium Behavior In Metal Titanium Film

Tritium is an element of considerable interest and has important technological applications, especially in the nuclear industry. The coexistence of helium and hydrogen isotope is inevitable in tritium-contained materials. The impact of helium on hydrogen in the materials has been widely investigated in experiment and theorety. It is well known that helium retained in the metals significantly decreases the diffusion, permeation and release of hydrogen isotopes. However, there are very few reports on hydrogen effects on the behavior of helium so far. In this thesis we focuse on the hydrogen effects on helium behavior in titanium, and the main reasearching results can be cataloged as following:1) The preparation of helium and hydrogen containing films is a precondition for this investigation. The first preparing method is that the helium and hydrogen are incorporated into the growing Ti films by DC magnetron sputtering in mixture of the working gasses H, He and Ar. The second is that firstly the helium-containing films is prepared using magnetron sputtering methods and then plasma hydrogenation is carried on to achieve the helium and hydrogen containing film. Both the methods can controllably achieve required H and He content which are dirstributed uniformly in the films with, and also the displacement damage due to helium introduction is low.2) The retained amount and depth profiles of helium and hydrogen were determined by ion beam analysis method. For the need of elemental analysis of helium and hydrogen, the elastic scattering cross-section for proton scattering from helium is measured at a laboratory angle of 165°and over an incident proton energy range from 1.6 to 3.6 MeV. The cross sections of 3.5-8.0MeV 1H(12C,1H)12C at 30°have also been measured. Both the total errors are less than 6%.3) Thermal desorption spectrometry was applied to investigate hydrogen on helium thermal release. The linear heating results indicate that at the low temperature region (300-900K), the peak corresponding to interstitial helium and helium-vacancy complex, and with increasing hydrogen content increase the helium release reduces gradually. When annealing at high temperature (900-1300K), high hydrogen content will reduce the release temperature with large amounts of He release. Considering to the XRD results, the films with 5at% H is?-Ti, while the film is?+?Ti at H content of 40at%. When the H content approaches saturation the film changing into ?-Ti completely. It is believed that the shift of release peak with large amounts of He toward lower temperature at high temperature regionis related to the crystal structures of the film and?phase structure degrades the mechanics properties of films to enhance the formation of helium bubble network.Then, we investigated the hydrogen effect on interstitial helium diffusion through the released fraction of helium during isothermal degassing of films. We found that the early stage of isothermal annealing belong to interstitial helium release process. Based on the diffusion equation we obtain the helium diffusion coefficient. In the same temperature, with the hydrogen content increases the helium diffusion coefficient decreases. We also use ion beam analysis to measure the helium concentration before and after annealing, and find that the helium content changes with different hydrogen contents.4) Hydrogen effects on helium behavior in hcp-type titanium and titanium hydride were studied using first-principles electronic structure calculations. The results show that the dissolved H atoms in hcp Ti and titanium hydride significantly change the formation energy of He interstitial sites but does not changes energetically favorable occupying site. The impact of hydrogen on the formation of He interstitial defects is directly related to the atomic environment around H atom and position relative to He interstitial atoms as well. It was found from the calculation that an octahedral interstitial He can more easily migrate along the indirect octahedral-tetrahedral-octahedral path than the other direct path of octahedral-octahedral, and that the activation energy for He diffusion turns out to be increased by 0.17 eV (from 0.22 to 0.39eV) when there exists a H atom in the first neighbor octahedral site of the He. Changing the number of H atoms from one to two needs a much higher energy for He diffusion. In the dissociation mechanism, whether there is hydrogen or not the helium fall sites between the vacancy and the interstitial sties. Hydrogen also increases the binding energy of helium and a vacancy and the diffusion energy. In titanium hydride helium migrated along the indirect tetrahedral-octahedral path. With the helium content increase the activation energy for He diffusion also increases. All these results indicate that the H around He interstitial site impedes the helium migration in hcp Ti and titanium hydride.