Abstract
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.
Highlights
Zirconium-based alloys are widely used as the main structural material in nuclear reactors due to low thermal neutron cross-section, high melting point, high corrosion resistance in water at 280–350 ◦ C and acceptable mechanical properties
The operation experience of nuclear reactors showed that zirconium alloys are subjected to corrosion and hydrogen embrittlement [1,2]
The rate of hydrogen uptake observed during corrosion is affected by the chemical composition of zirconium alloys and by their microstructure and surface oxide morphology [5,6]
Summary
Zirconium-based alloys are widely used as the main structural material in nuclear reactors due to low thermal neutron cross-section, high melting point, high corrosion resistance in water at 280–350 ◦ C and acceptable mechanical properties. The operation experience of nuclear reactors showed that zirconium alloys are subjected to corrosion and hydrogen embrittlement [1,2]. Hydrogen is generated during water radiolysis and corrosion reaction between zirconium and water under reactor operation. Hydrogenation of Zr alloys to local or total critical concentrations leads to embrittlement of fuel claddings caused by brittle hydrides precipitations [3,4]. It has been shown that un-oxidized particles precipitated at the oxide/metal interface may act as preferential paths for hydrogen permeation to the metal matrix [7,8]. It has been shown that cracks formed in the oxide layer result in hydrogen enrichment close to the metal surface [11]
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