| The traditional zirconium alloy cladding materials of pressurized water reactor are apt to react violently with water vapor at high temperatures,accompanied by exothermic heat and hydrogen.The explosion in the Fukushima nuclear accident resulted from this reason.As a new type of accident-tolerant safety cladding material,Fe-Cr-Al alloy has received extensive attention in recent years.Fe-Cr-Al alloy not only has high strength and toughness,but also has good high temperature oxidation resistance.Nuclear reactor cladding materials are subjected to extreme water chemistry under high temperature,high pressure,corrosion and particle irradiation,and their corrosion resistance is the primary problem to be met.At present,there are relatively few reports on the corrosion performance of Fe-Cr-Al alloy,and the influence of Al and Cr on the corrosion mechanism is still unclear.The numerical simulation can be used to easily study the corrosion behavior of the alloy and predict the long-term corrosion behaviors of the alloy.Therefore,this paper combines simulation and experimental study to estimate the corrosion resistance of Fe-Cr-Al alloy,and the effects of alloying elements Al and Cr on the corrosion resistance are also inverstigated.The electrochemical corrosion of Fe in solution environment was simulated and calculated by COMSOL and FLUENT software.It was found that under acidic conditions,H+acts as a depolarizer to corrode Fe.The lower is the pH value,the higher is the corrosion current density of the system and the faster is the corrosion reaction.The depolarizer under alkaline conditions is O2,and Fe forms a complex at high pH.Therefore,as pH increases,the corrosion current density of the system increases slowly first,and then increases rapidly,indicating that the corrosion of Fe increases.The corrosion rate of Fe in the acid solution is much larger than that of the alkaline solution;the fluid flow rate mainly forms stress corrosion on Fe,and the temperature and oxygen concentration have a great influence on the corrosion of Fe.With the increase of temperature and oxygen concentration,the corrosion rate of Fe is greatly improved.We set a coupling field solution with a pH of 7.2,an oxygen concentration of 0.05 mol/L,a temperature of 400 K,and a fluid flow rate of 0.5 m/s,the corrosion simulation of Fe-Cr-Al alloy was in this solution,it was found that the Al-rich zone was rapidly corroded.Corrosion products are mainly deposited in and around Al with low equilibrium potential.Cr is affected by the corrosion deposition of Al,and the corrosion is also serious.The matrix Fe is protected by Cr and Al with more negative electrode potential,and thus Fe is not seriously corroded.The increase of Al content makes the deposition of corrosion products distribut more uniform,which improves the corrosion resistance of the alloy.The increase of Cr content can increase the deposition of corrosion products on Fe surface,thus improving the overall corrosion resistance of the alloy.Under the simulated conditions,the overall deformation of the alloy surface is very small,indicating that the Fe-Cr-Al alloy has good corrosion resistance.The corrosion performance of Fe-Cr-Al alloy in 200ml H2O+0.55ml concentrated H2SO4+3gFeCl3 is very poor.The maximum corrosion rate of Fe-12Cr-2Al after immersion for 120h is 25.913mm/a,and the surface is cracked along the grain with crack depth up to mm level.Through the XPS analysis of the alloy surface,the corrosion products of the alloy are mainly composed of Al2O3 and Cr2O3,there are a small amount of complex oxides of Fe and Cr,and the oxidation degree of the surface of the alloy increases with the content of Al and Cr.When the thickness of oxidation film is increased,the corrosion rate of the alloy obviously slows down and the corrosion resistance is enhanced.The corrosion depth of the alloy is less than 50 nm in the case of Fe-12Cr-6Al.The corrosion performance of Fe-Cr-Al alloy in LiOH+H3BO3 solution with pH=7.2 is good.After soaking for 360h,the surface of the alloy has metallic luster.The Fe-Cr-Al alloy exhibits good corrosion resistance in alkaline solution.Al and Cr have almost the same effects on the corrosion of Fe-Cr-Al alloy.The oxides are formed on the surface of the alloy to prevent direct contact between the alloy and the etching solution.The oxide film of Al is easier to form than Cr,because the change in Al content gives the system a greater corrosion current density in solution.Within the range of the studied components,Al has a greater influence than Cr on the corrosion performance of Fe-Cr-Al alloy. |
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