Damage Characteristics Of Titanium Deuteride Film Irradiated By Pulsed Ion Beam

The constant yield of a D-D or D-T type neutron generator is largely limited to the performance of its target. The fundamental problem of increasing the servce life of a neutron generator and the urgent need for the optimal design and sustainable development for a high-intensity neutron generator require the exploration of the impact of ion beam on the properties of target. In this thesis, we mainly focus on the basic phenomenon observed in the interaction between ion beam and solid target, and conduct a discussion to the degree of both thermal and irradiation damages brought to the target under extrme condition of current beams. Based on the researches of damages of titanium deuteride film irradiated by pulsed ion beam, the irradiation enduced transformations of surface morphologies, phase structures and irradiation defects have been subsequently investigated, and combined with numerical simulations of thermal-mechanical coupling effect and damage of irradiation, mechanisms of the interaction between beam and solid target have been further clarified, and the the main results can be cataloged as follows:1、The characteristics of surface morphologies of titanium deuteride films under irradiation have been investigated, and changes of morphologies have been studyed.Titanium deuteride films are irradiated with pulsed ion beams for several shots at energy densities of0.1J/cm2,0.3J/cm2and0.5J/cm2, respectively. The grains of titanium deuteride have been smoothed after20shots under irradiation at0.1J/cm2; a slight meltting of the grains has been detected on the irraditaed surface at0.3J/cm2; a feature of intense melting and network cracks can be observed on surface morphologies after energy density reaches0.5J/cm2, but a serve ablation has not been comfimed by the energy dispersive X-ray spectroscopy analysis of the specific zone, in which the white dots of ejection have been recognized as the ablation product of annode materials.Surface roughnesses of films are reduced in all three cases, and the higher the energy density is the more profound the effect will be, which makes us believe that although a noticeable effect of thermal damage may not be induced by a single shot of pulsd ion beam, the cumulative effect of repetitive shots can still make a difference.Frictional coefficient on the surface of scratch test is reduced under repetitive irradiations. The repeated melting of the surfae layer makes the scratch revealing a more smoothed and densified texture, and can also improve both of its hardness and toughness, alleviating the plastic deformations.2-. A numerical simulation of the thermal effect of the pulsed ion beam on titanium deuteride film has been conducted, and a model of thermal-mechanical coupling effect has been introduced.Thermal-mechanical effect during the shots of pulsed ion beam has been estimated by finite element analysis. Temperature rise at the top node under irradiation of0.1J/cm2is well below melting point, and irradiation of0.3J/cm2is just beyond melting point, and irradiation of0.5J/cm2is well beyond melting point. Results of simulation coincide well with the phenomenon of melting observed by SEM.Thermal stress is most prominent at the surface, and decreses rapidly along depth direction, but different thermal expansion coefficients between the film and substrate have made the stress at the interface present a discrepancy, which suggests that the interface tends to be badly affected under shots of pulsed ion beam, leading to the separation between film and substrate. The maximum displacement of thermal expansion is located at the side boundaries, as only the inner side is subjected to constraint. Results of simulation make a well explanation for the network cracking observed by SEM and the evolution of residual stress, and confirms that the thermal-mechanical coupling effect accounts for the server thermal damage on the irradiated surfaces.Additionally, the well known phenomenon of "selective ablation" has been explained through the perspective of numerical simulation, in which two types of protrsions, triangular and semicircle, have been investigated. The degree of "selective ablation" presents positive and negative relations with h and t respectively in the triangular model, while increases at first, then decreases with r for the semicircle. Finally, influences of both the duration of pulse and the diffusion length of heat on the degree of "selective ablation" have been evaluated, and we finally arrives that the degree of "selective ablation" depends on the competition between the rate of energy deposition and diffusion efficiency of heat.3、Characteristics of the transformation of phase structures and the desorption of hydrogen isotopes in the film under irradiation has been investigated.A metastable bct TiD2(x) phase formation in the fcc titanium deuteride is kinetically favored by the ultra-fast heating and cooling rate achieved by the pulsed ion beam irradiation. X-ray diffraction analysis reflects that a noticeable decomposition of titanium deuteride, precipitation of alpha titanium and transformation of a metastable hydride phase take place once energy density of pulsed ion beam reaches0.5J/cm". However, it appeares that the bet TiD2(x) phase is stable only at high temperature, and all quenching experiments result in the formation of equilibrium phases. The non-equilibrium thermodynamic process of high-temperature and high-pressure induced by pulsed ion beam irradiation facilitates the transformation of fcc titanium deuteride into metastable bct TiD2(x) phase.Deuterium atoms tend to accumulate to the surface under repeated shots other than be simply depleted. Results of secondary ion mass spectroscopy demonstrate that almost no depletion of deuterium can be observed on the irradiated surface, although diagrams of XRD for the sample at irradiation of0.5J/cm2have indeed demonstrated the precipitation of pure titanium and the desorption of deuterium. Interpretations for this phenomenon is that the top deuterium might be released swiftly during irradiation, but repeated shots can compensate for the loss of deuterium by driving the migration of hydrogen sotopes from deeper region.4、Creation of irradiation defects of titanium deuteride films under repetitive shots has been studyed, and its mechanism has been explored.S parameter in doppler broadening spectra of slow positron annihilation indicates the procedure of impregnating pure titanium film with deuterium has introduced the film with quite a mount of defects. The treatment of pulsed ion beam can also introduces in great mount of irradiation defects, and the concentration peaks within0.5μm from the top. Concentration of defects, as calculated by TRIM, rises with the increase of energy density and shot number. However, in pratical cases, the repeated melting and crystallization of the surface titanium deuteride, as observed in SEM, may anneal most of the irradiation defects, leading to the decrease of S parameter to its original state.