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Hydrogen Interaction with Deep Surface Modified Zr-1Nb Alloy by High Intensity Ti Ion Implantation
(2018)
A deep surface modified TiZr layer was fabricated by high-intensity low-energy titanium ion implantation into zirconium alloy Zr-1Nb. Gas-phase hydrogenation was performed to evaluate protective properties of the modified layer against hydrogen permeation into Zr-1Nb alloy. The effects of ion implantation and hydrogen on microstructure, phase composition and elemental distribution of TiZr layer were analyzed by scanning electron microscopy, X-ray diffraction, and glow-discharge optical emission spectroscopy, respectively. It was revealed that TiZr layer (~10 μm thickness) is represented by α′ + α(TiZr) lamellar microstructure with gradient distribution of Ti through the layer depth. It was shown that the formation of TiZr layer provides significant reduction of hydrogen uptake by zirconium alloy at 400 and 500 °C. Hydrogenation of the modified layer leads to refinement of lamellar plates and formation of more homogenous microstructure. Hydrogen desorption from Ti-implanted Zr-1Nb alloy was analyzed by thermal desorption spectroscopy. Hydrogen interaction with the surface modified TiZr layer, as well as its resistance properties, are discussed.
A high-intensity metal ribbon ion beam was generated using plasma immersion extraction and the acceleration of the metal ions with their subsequent ballistic focusing using a cylindrical grid electrode under a repetitively pulsed bias. To generate the dense metal plasma flow, two water-cooled vacuum arc evaporators with Ti cathodes were used. The ion current density reached 43 mA/cm2 at the arc discharge current of 130 A. High-intensity ion implantation (HIII) with a low ion energy ribbon beam was used for the surface modification of the aluminium. The irradiation fluence was changed from 1.5 × 1020 ion/cm2 to 4 × 1020 ion/cm2 with a corresponding increase in the implantation temperature from 623 to 823 K. The structure and composition of the Ti-implanted aluminium were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX). The mechanical properties and wear resistance were measured using nanoindentation and “pin-on-disk” testing, respectively. It was shown that the HIII method can be used to form a deep intermetallic Al3Ti layer. It has been established that a thin (0.4 μm) modified layer with a hcp Ti(Al) structure is only formed on the surface at 623 K, while the formation of the ordered Al3Ti intermetallic phase occurs at the implantation temperatures of 723 and 823 K. Despite the significant ion sputtering of the surface, the thickness of the modified layer increases from ~1 μm to ~6 μm, and the implantation temperature rises from 723 to 823 K. It was found that the homogeneous intermetallic Al3Ti layer with a thickness of up to 5 μm was formed at 823 К. The mechanical and tribological properties of the aluminium were substantially improved after HIII. For the Ti-implanted aluminium, the hardness of the surface layer increases from 0.4 GPa (undoped Al) to 3.5–4 GPa, while the wear resistance increases by more than an order of magnitude.
The Fukushima disaster has strongly effected on nuclear energetics and their progress [1]. It pointed to a crucial oxidation and subsequent destruction of nuclear fuel claddings in light-water reactors in the case of loss of coolant accident conditions. Surface modification is one of the promising approaches to protect Zr alloys in normal operation and accident conditions of nuclear reactors [2]. Surface modified layers or coatings forming chromia during oxidation is of greatest interest since it meets the basic requirements for accident tolerant fuel materials [3]. The aim of this research is to study the possibility of deep surface modification of zirconium alloy E110 by high intensity ion implantation using low energy metal ion beam.
The formation of the metal ion beams is provided by the application of negatively pulsed bias (1.5 kV) to the system immersed in the chromium vacuum arc plasma. The structure and composition of Cr-implanted zirconium alloy were studied by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The mechanical properties and wear resistance were measured by nanoindentation and «ball on disk» testing, respectively. The influence of implantation temperature on the phase composition, microstructure, and mechanical properties as well as on the corrosion behavior of Cr-implanted zirconium alloy under high-temperature oxidation (up to 1100÷1200 °C) have been described.
This work describes the effect of high-intensity low ion energy implantation on the structure and properties of the surface modified layer forming on zirconium alloy. The influence of irradiation dose on the microstructure, phase composition, thickness and mechanical properties of surface modified zirconium alloy were investigated.