The Preparation And Corrosion Resistance In Pb-Bi Alloy Of SiC Films On 15-15Ti Steel

15-15 Ti steel was selected as the candidate cladding material of Chinese lead fast cooling reactor because of its good antiradiation performance,mechanical and processing properties.However,the corrosion resistances of 15-15 Ti steel still does not meet the complex corrosive environments in the reactor.The Al₂O₃/SiC bilayer films and Ti TiN/SiC functional gradient films were deposited on 15-15 Ti steel by magnetron sputtering.The structures,morphologies and properties of the films were measured by XRD,AFM,FESEM,EDS and microhardness tester.At the same time,corrosion tests of before and after coating 15-15 Ti steel were carried out in a oxygen concentration of 1�10-6 wt.% Pb-Bi alloy solution at 500 �C for 500 hrs and 1000 hrs,the corrosion morphologies,corrosion products and corrosion layer thickness of coated and uncoated 15-15 Ti steel after corrosion were studied by XRD,FESEM and EDS analysis.The results show:?1?Al₂O₃/SiC bilayer thin films and Ti/TiN/SiC functional gradient films prepared on the surface of 15-15 Ti steel by magnetron sputtering are continuous and compact,and there are no obvious defects.The film microhardness were 12.5Gpa and 17.0Gpa respectively.?2?The structures,morphologies and compositions of uncoated and coated 15-15 Ti steel with Al₂O₃/SiC bilayer thin films for 500 hrs and 1000 hrs in Pb-Bi alloy solution at 500�C are tested.It is found that uncoated 15-15 Ti steel has been corroded in Pb-Bi alloy solution at 500�C for 500 hrs,and its surface appears Fe3O4 corrosion layer of 1.1um thickness.Moreover,the uncoated 15-15 Ti steel is corroded for 1000 hrs at the same conditions,its surface appears Fe3O4 and?Fe,Cr?3O4 corrosion layers of 2.5um thickness.However,15-15 Ti steel coated with Al₂O₃/ SiC bilayer thin films is not been corroded in Pb-Bi alloy solution at 500�C for 500 hrs and 1000 hrs,its surface oxidation does not occur,the corrosion resistance of Al₂O₃/SiC bilayer thin films is good.?3?Compared the uncoated and coated 15-15 Ti steels with Ti/TiN/SiC functional gradient films in Pb-Bi alloy solution at 500 �C for 1000 hrs,the uncoated 15-15 Ti steel has been corroded,and its surface appears Fe3O4 and?Fe,Cr?3O4 corrosive products of 2.1um thickness.However,there was no oxidation on the surface of 15-15 Ti steel coated with Ti/TiN/SiC functional gradient films after corrosion in Pb-Bi alloy solution at 500�C for 1000 hrs.?4?After continuous 1000 hrs corrosion in Pb-Bi alloying solution at 500 �C,there was not Pb-Bi permeation into Al₂O₃ buffer layer of Al₂O₃/SiC bilayerthin films,but a small amount of Pb-Bi permeation into the Ti/TiN buffer layers of Ti/TiN/SiC functional gradient films.This indicates that the Al₂O₃ buffer layer is more closed,the corrosion resistance of Al₂O₃/SiC bilayer thin films is better than that of Ti/TiN/SiC functionally gradient films.The results have accumulated experiental data and theoretical analysis for the subsequent evaluation of the corrosion performances under Pb-Bi alloy and surface modification of 15-15 Ti steels.