Reconstructing brittle hydrides using pulsed electric current to restore the degraded performance of zirconium alloys

Abstract

When zirconium alloy undergoes water corrosion reaction during the service process, it absorbs hydrogen to form brittle hydrides, which is one of the main reasons for the deterioration of the mechanical properties of zirconium alloy. There is an urgent need to find an effective method to regulate brittle hydrides to restore the properties of hydrogen-containing zirconium alloys. This study conducted electropulsing treatment on the hydrogen-charged nuclear grade Zr-4 alloy, and the results showed that the electropulsing process caused the hydrides to transform from large-sized brittle stripe-shaped δ-phase to the small-sized ζ-phase. The hydrogen content in the alloy is significantly reduced, which basically restores the mechanical properties of the alloy. However, in the comparative experiment of isothermal heat treatment at 400 °C, brittle hydrides did not dissolve and their mechanical properties did not recover. A mathematical model was established for the characteristics and morphological changes of strip hydrides, and the current density distribution and introduced free energy during the microstructure evolution process were calculated and analyzed. The calculation results indicate that the pulsed current promotes the decomposition of hydrides through the introduction of free energy, reduces the activation energy of hydrogen atom diffusion, accelerates the diffusion and desorption of hydrogen atoms, and realizes the repair of mechanical properties of hydrogen-charged zirconium alloy.