Effect Of Nitridation On Uranium Titanium Interface

Uranium has many important applications in nuclear fuel fields. However, because of the special electronic configuration, uranium have high chemical activity and poor corrosion resistance. An effective means of anti-corrosion is to prepare films on the surface of uranium by physical vapor deposition method. But in actual production process, oxide layer will be formed on the film-substrate interface because uranium is easy to oxidize. This will produce adverse effects on adhesion strength of film in long-term application. In this paper, plasma nitriding technology was used as pre-treatment, and Ti films were prepared on the surface of uranium and uranium nitride by magnetron sputtering for comparison. The films were characterized and analysed by X-ray diffraction (XRD), scanning electron micrograph (SEM), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The effects of nitriding pre-treatment for the film were studied. The ability to resist corrosion and adhesion strength of film were analysed by electrochemical analysis and indentation method.XRD test was carried on to study the composite of uranium nitride. The results indicate that there is mainly U2N3 on the surface. A series of processes should be used between plasma nitriding and depositing film. AES was used to investigate the stability of uranium nitride in these processes. There was no significant change in the processes of placed in the atmosphere and baked in vacuum. Changes were observed in the process of argon ion sputtering. So 1.5 kV,16 kV and 36 kV argon ion were used to sputter the uranium nitride and the effects of ion sputtering were studied by XPS. As the energy increased, the composition of surface changed form UNxOy to UO2 and UO2+x. The oxidized degree of surface increased. However, the effect of ion sputtering were mainly on the surface of uranium nitride. Ion sputtering didn’t affect the structural integrity of uranium nitride.Titanium films were prepared on the surface of uranium and uranium nitride by magnetron sputtering. Different preferred orientation growth is attributed to different substrate structure. The structure of the interfaces were studied by XPS depth profiling. Uranium and uranium oxide were exist on the interface of U-Ti, and very thin oxide layer exist on the interface of U2N3-Ti.The thickness of oxide layer decreased after the nitriding pre-treatment. The oxygen on the interface of U2N3-Ti is difficult to diffuse. That is good for bonding strength of film. The AES analysis of U2N3-Ti prepared in high vacuum environment shows the regulation of nitriding pre-treatment. The thickness of oxide layer is in the range of AES. The peak of nitrogen moves towards high energy side, that means lower valence state. The nitrogen may combined with Titanium.The corrosion resistance of different films were studied by electrochemical analysis. The titanium film on the uranium nitride has higher corrosion potential, larger slope in the potentiodynamic polarization curves; has larger capacitive reactance arc in the electrochemical impedance spectroscopy than titanium film on the uranium. Bonding strength of films were studied by indentation methods. The surface crack appeared on U-Ti when the press is 3 N, and the surface crack appeared on U2N3-Ti when the press is 5 N. The adhesion strength of each film were calculated to be 278.45 MPa and 322.59 MPa. The titanium film on the uranium nitride has higher adhesion strength than titanium film on the uranium.