| As the cladding materials of nuclear reactor fission materials,Zirconium alloy is the first barrier of nuclear power safety protection.Irradiation damage,high temperature and high pressure water corrosion,hydrogen corrosion etc.are the important factors which cause the failure of the alloy cladding tube.In order to prolong the service cycle of Zirconium alloy and meet the performance requirements of high burnup,lots of research has been done for the oxidation process and protective coating on Zirconium alloys.The corrosion resistance of Zirconium alloys influenced by second precipitates significantly.Ti2Ni-type?Zr,Nb?2Fe and C14-type Zr?Nb,Fe?2 are main second precipitates of E635 and Zirlo respectively.In this paper,by non consumable vacuum arc melting method,the second phase has been melted separately.Then,the second phase alloy corroded under simulated nuclear pressure reactor conditions about320°C and 16.4MPa.XRD TEM and SEM were employed to study the process of the oxidation and microstructure of oxidation film.This research is helpful for a better understanding of the important role of alloying elements in the oxidation process and the properties of the second phase material.This is meaningful to improve the corrosion resistance of Zirconium alloy.Corrosion oxidation experiments of?Zr,Nb?2Fe show that the second phase material has poor crystallinity and the oxidation film are monoclinic zirconia and tetragonal zirconia.The main oxidation products nearby oxidation/water interface are monoclinic zirconia and amorphous zirconia.Dislocations and micro-faults also found in monoclinic zirconia.The line EDS analysis show that accumulation of iron at middle oxidation film.Microstructure studied by HRTEM indicated the orientation relationship?OR?between iron??-Fe?and tetragonal zirconia: [010]t-ZrO2//[001]?-Fe,?200?t-ZrO2//?110??-Fe and the mismatch: 4dt?200?=5d??110?.The OR delay the martensitic transformation of tetragonal zirconia to monoclinic zirconia.Tetragonal zirconia nextto the iron forms nano-crystalline eventually.The fact that tetragonal zirconia could be stabilized by iron was further verified by the ternary compounds with different iron content.In this research Zr?Nb,Fe?2 phase content has been optimized and corrode under simulated nuclear reactor 20h/40h/60 h.The oxide film thickness about 1.2?m and have no significant difference with different corrosion time.Through the observation of the cross-section of oxide film at different time by SEM,it is found that the phase structure of the oxide film is compact and has no obvious crack.With the TEM observation of the oxide film section,the main structure of the oxide film is inside amorphous oxide and surface crystalline oxide,and the oxide structure forming mechanism is analyzed and discussed.The amorphous oxide is compact the thickness is more than 100 nm,and increasing with the corrosion time.The oxide film is a certain barrier on the diffusion of oxygen ions to the metal matrix further,which indicates that Zr?Nb,Fe?2 alloy is a potential material for Zr alloy coating.In this paper,the corrosion resistance of two kinds of phases was evaluated by electrochemical method.The results show that the properties of the alloy are better than those of the commercial alloy.By comparing the high temperature and high pressure water corrosion behavior and electrochemical corrosion properties of two kinds of,it is found that the corrosion performance of Zr?Nb,Fe?2 phase is better,and its oxide film is thinner and more compact.On the basis of this,the Zr-FeNb three alloy coating with Zr?Nb,Fe?2 contents was prepared on the surface of Zr-4 alloy by HiTUS.The structure of the thin film is compact and has no obvious defects.The main structure of the film is amorphous and nano-crystalline,which is proved by the electrochemical method that the coating has a certain protective effect on the matrix alloy. |
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