Study Of Helium Behavior In Al And Ti Alloys By Small Angle X-ray And Neutron Scattering

The purpose of this dissertation is to explore the state of helium atom in boron doped and neutron irradiated aluminum (r-Al (He)) and helium containing titanium film (m-Ti (He)) prepared by magnetron sputtering method, and to develop the small-angle scattering (SAS) experiments and data analysis techniques for helium evolutionary behavior research combining with transmission electron microscopy (TEM) techniques to verify the reliability. More attentions were paid on preparation of helium containing boron-doped aluminum sample and its helium evolution. Helium behavior in Ti and TiMo alloys film prepared by magnetron spattering were studied with SAS under different annealing temperature. This work is an useful reference of SAS technology on helium behavior in materials. The details are summarized briefly as follows:(1) Development of small-angle scattering techniques. Effect of in situ loading on sample decorates signals from the specimen. This influence is reduced by using a combination of instrument setups, and the real SAS information is extracted. A two-dimensional Gaussian fitting method was introduced in the recognition of direct beam center and has a better reproducibility than the existing package Fit2D, which effectively reduced the uncertainty of beam center. A versatile package for small-angle scattering data analysis was developed and filled the domestic gap of this field. Its rich SAS model, flexible data manipulation and function extension greatly reduced the burden of SAS data analysis.(2) He-containing Al-B material was produced via thermal neutron irradiation by using the (n, a) reaction of10B, in which the density of He atoms reaches to6.2×1019cm-3helium concentration of Al-B. He bubbles inside the material were characterized by SAXS and TEM after thermal stimulation. The SAXS results show that the size distributions of He bubbles are almost similar, but the volume fraction increased in the sample after400℃and500℃thermal treatments. Metal samples tempered at600℃for about1h yield the largest fraction of He bubbles. By contrast, the samples tempered at700℃for about1h exhibits a further increased in He bubble diameter, but sharply decrease in volume fraction, wich is attributed to burst bubbles and escaped He from the Al-B sample at high temperatures. A similar size distribution is observed by TEM, but the most possible diameter decreased by3.9nm. This discrepancy is caused by poor statistics of TEM with a reduced view and the poor discrimination of aggregated He bubbles from SAXS measurements. XRD and neutron diffraction show that there does not exist second phase in the samples before and after irradiation, but doped boron atoms make the lattice increase and the introduction of helium by neutron irradiation makes the lattice further increased due to the generation of Li and He atoms. Thermal treatment of irradiated sample released but not recovered the lattice expansion. The geometrical optimization by first-principles calculations provides a explanation of this lattice changes.(3) For the first time SAS technique was applied to the research of helium containing titanium film Ti(He) system, and revealed the helium bubble state in titanium films with different helium concentration under different thermal treatments. The results show that the helium concentration is proportional to the He/Ar flow ratio when sputtering the film of Ti00, Ti0.5, Ti1.0, Ti15. SAXS analysis shows there is a significant increase in the intensity of scattering pattern of He introdued and anisotropy scattering due to the precipitation and the capsule-shaped void occurs in the basal plane of HCP Ti. The helium bubbles grow up with the temperature increase. TEM observation verified SAXS analysis. SAXS analysis of in situ tempering sample shows that SAXS curve changed apparently with the different He/Ar ratio at room temperature whereas smoothed when the temperature increase. Analysis of several q range show that:1) the more He content in sputtering gas, the higher intensity from helium bubbles;2) the large-scale (25-31nm) scattering signal enhanced with increasing temperature. This Indicates that the temperature accelerates the helium bubble growing up. SAXS analysis of sample with off-line thermal treatment shows that the temperature of growing and bursting of helium bubble is consistent with the result of thermal desorption spectroscopy. In the helium desorption temperature zone, the helium volume fraction decreases significantly and the average size of bubble is affected to a certain extent. The variation of helium bubble size and volume fraction by SAXS is consistent with the desorption temperature of TDS. The volume fraction of helium bubble is significantly reduced in the desorption temperature.