脉冲离子束辐照对TiH_2膜表面微观结构的影响

EFFECT OF IRRADIATION WITH PULSED ION BEAM ON THE MICROSTRUCTURE OF TiH_2

在TEMP-6型强流脉冲离子束装置上,利用能量密度0.1-0.5 J/cm^2,脉宽100 ns,能量100 keV的C^+和H^+混合离子束对TiH_2膜进行逐次轰击以研究其在脉冲能量下的稳定性.采用扫描电镜和表面轮廓仪对TiH_2膜辐照前后表面形貌进行研究;利用X射线衍射和慢正电子湮没技术对脉冲离子束辐照前后TiH_2膜的物相和缺陷结构进行分析.结果表明:0.1-0.3 J/cm^2的脉冲束流辐照热-力效应不足以导致膜明显熔化和开裂;0.5 J/cm^2的脉冲束流辐照致使膜明显熔化并伴随产生大量的网状裂纹.0.1-0.3 J/cm^2的脉冲辐照条件下TiH_2的物相结构未发生明显变化,而0.5 J/cm^2条件下δ-TiH_2开始发生向体心四方(bct)结构的非平衡相变,并且随着辐照次数的继续增加膜内开始析出纯Ti的物相.脉冲束流辐照下的热-力学效应导致膜内缺陷的分布发生显著改变,导致膜的慢正电子Doppler展宽谱的S参数在0.5 J/cm^2 5次轰击时达最小,而在0.3 J/cm^2 1次轰击时最大.

Titanium has long been of interest as hydrogen storage material since titanium has a high affinity to hydrogen isotopes. Titanium deuteride or tritide is an important nuclear material used in the field of nuclear technology. Investigations concerning hydrogen-titanium system seem to mainly focus on the hydrogen thermal desorption spectra so as to study hydrogen desorption kinetics from metal hydride and to determine the rate controlling step, but little is known on the evolution of its compositional changes under a much more un-equilibrium condition. In the past two decades, the intense pulsed ion beam （IPIB） technique has received extensive attention as a tool for surface modification of materials. Compared with conventional ion implantation, IPIB irradiation into ma- terials possesses a higher energy density with shorter pulse width and be typical of more intense thermal-mechanical effect. From such a point of view, considering the features of extreme high heat- ing and cooling rate of IPIB, IPIB as a method to evaluate the stability characteristics of titanium hydride film is utilized in order to determine a predictable behavior of the film＇s evolution under an extreme un-equilibrium external condition. In current study, Till2 films irradiated by intense pulsed ion beam have been investigated by using scanning electronic microscopy, surface profilometer, X-ray diffraction and slow positron annihilation, in order to evaluate the effect of irradiation with pulsed ion beam on the microstructure of Till2. Three sets of Till2 films are irradiated several shotsat energy density ranging from 0.1 J/eln2 to 0.5 J/cm2. No noticeable phenomenon of melting and change of phase structures have occurred to samples under irradiation of 0.1 0.3 J/cm2. However, phenomenon of melting and indication of cracking has been detected on the surface after energy density reaches 0.5 J/cm2. Besides, desorption of hydrogen from the film, and a titanium hydride with a body centered tetragonal structure （bet）, seldom reported by researchers and formed under extreme conditions, has also been identified only after energy density of IPIB reaches 0.5 J/cm2. S parameter of slow positron annihilation reflects that the crystal defect structures have been greatly changed by IPIB irradiation, in which S parameter reaches a large value at 0.3 J/cm2 with 1 shot, while a small one at 0.5 J/crn2 with 5 shots.