Preparation And Performance Study Of Chemical Plating And Pre-plating Of Zirconium Alloy For Nuclear Us

Zirconium has been widely used as cladding material for nuclear fuel in the area of nuclear technology because of it’s low neutron absorption cross-section,high-melting-point and excellent corrosion resistance.In recent years,the development of accident resistant fuel(ATF)has become a research hotspot,especially the study of improving the high-temperature oxidation resistance of cladding materials.Electroless plating technique is widely used in coating preparation.This is a chemical deposition technique with lower equipment requirements,simple operation and excellent plating quality when it is compared to electrodeposition.Electroless plating technique is widely used in various fields and is an effective method to improve the corrosion resistance of zirconium alloys.Therefore,the study of electroless plating on the surface of zirconium alloys has very important practical value.However,zirconium has less ability to ditch an electron than titanium in the same main group,which makes it difficult to deposit electroless plating on the surface of zirconium alloys.Furthermore,the electroless plating on the surface of zirconium alloys is rarely studied.So this paper introduces the research of pre-plating technology and studies two pre-treatment technology:phosphating and Fluoride-phosphate chemical conversion.Complete and dense film will be prepared on the surface of zirconium alloy.It was found that in the phosphating treatment process,when the temperature and time exceeded a certain threshold,the phosphating film would be porous.The optimal experimental parameters of phosphating treatment were as follows:when the temperature was 50℃,the time was 4min,and the NaF content was 1.5g/L,the phosphating film obtained was uniformly dense and the deposition rate was relatively high.The phosphating film is amorphous structure,and crystalline structure was appeared when the temperature exceeds 50℃.The average microhardness of phosphating film was 176.5HV,and the microhardness first increased and then decreased with the temperature(time).There is little difference in corrosion resistance between substrate and phosphating film,but the substrate can be protected with phosphating film to some extent.In the fluorine-phosphate chemical conversion process,the optimal technological parameters are:Na3PO4 concentration of 40g/L,conversion temperature of 30℃,NaF concentration of 15g/L.Reaction time has little effect on the quality of fluoride film.At 30℃,the fluoride film is amorphous.At 50℃,the microstructure of the membrane completely presents a crystalline structure.The hardness of fluoride film layer increases first and then decreases with Na3PO4 concentration(NaF concentration),but the decrease is not large,and the hardness can reach up to 259.8HV.Three kinds of Ni-P series chemical coatings were prepared with the thickness of 10-20μm.The microstructure of the coating is amorphous mixed crystal structure.Among them,the fluoride precoating+Ni-W-P coating protection system has the best corrosion resistance,has a well protective effect on the substrate,and the chemical coating and precoating has the highest binding force,up to 49.75N.