First-principles Study On The Effect Of Cu On The Microcracks And Micropores In The Oxide Film Of Zirconium Alloy

Zirconium alloy is used as nuclear fuel cladding material,and its corrosion resistance has an important influence on its life.Adding a trace amount of Cu to some zirconium alloys can greatly improve their corrosion resistance.However,the mechanism by which Cu affects the corrosion resistance of zirconium alloys is still unclear.The corrosion resistance of zirconium alloy is closely related to the microcracks and micropores in the oxide film.Therefore,this dissertation combines first-principles calculation and thermodynamic method to study the influence of Cu on the formation of microcracks and micropores in the oxide film,in order to understand the influence mechanism of Cu on the corrosion resistance of zirconium alloys.The main conclusions of this dissertation are as follows:(1)By calculating the segregation energy,it is found that Cu can segregate in the zirconium alloy oxide film.Using the first-principles computational tensile tests,it is found that when the amount of Cu segregation at the grain boundary is low,the tensile strength of the grain boundary can increase after Cu segregation,and the generation of microcracks at the grain boundary be inhibited,thereby increasing the corrosion resistance of zirconium alloy.This is consistent with experiments that adding an appropriate amount of Cu to the zirconium alloy can improve the corrosion resistance.(2)The influence of different content of Cu on the formation of microcracks is studied.Studies show that when the grain boundary Cu atom density is lower than 6.5atom/nm~2,the segregation effect can inhibit the formation of microcracks,resulting in better corrosion resistance.When the grain boundary Cu atom density is higher than6.5 atom/nm~2,the segregation effect can promote the formation of microcracks,resulting in poor corrosion resistance.It can be inferred that when the Cu content in the alloy is high,the high-concentration Cu segregation at the grain boundary is easy to form,which promotes the formation of microcracks and adversely affects the corrosion resistance.(3)The effect of a small amount of Cu on the grain boundary micropores is studied.Studies show that the segregation of Cu with a lower content(?1.6 atom/nm~2)inhibits the generation of micropores,and the segregation of Cu can also inhibit the generation of micropores in the presence of a lower content of H.From the perspective of the formation of micropores,Cu can improve the protection of the oxide film,which in turn can improve the corrosion resistance of the Zr alloy.In summary,the results of this dissertation show that adding a trace amount of Cu can increase the difficulty of the formation of microcracks and micropores,and improve the corrosion resistance of zirconium alloys.But the increase in Cu content can promote the formation of microcracks.This is consistent with the experimental results that the corrosion resistance of zirconium alloys is the best when a trace amount of Cu is added.