Study Of Welded Joint Layer Of Nb-1Zr Alloy And Stainless Steel

In nuclear industry, the welding problems of niobium alloy and stainless steel have been highly concerned. Because the property of niobium alloy is far from that of stainless steel, some special welding techniques have been applied, such as explosive welding, vacuum braze welding, electric resistance welding, vacuum electron beam self-material brazing and so on. In the interface an interdiffused layer with multphases would be formed during the process of welding or operation at elevated temperature. Because of so much difference between the interdiffused layer and the original interface layer, it would influence the welding strength severely. Therefore, in order to understand the long-time performance of the weld, it is necessary to study the welding interface of niobium alloy and stainless steel, and know the microstructure evaluation.Explosive welding and vacuum electron beam self-material brazing were used to prepare the specimen. The explosive welding specimen were also annealed in vacuum at various elevated temperature from 1000℃ to 1300℃. Optic microscope, SEM, TEM and EDS(electron diffraction scattering) techniques are applied to observe the microstructure and the element profiles of the welding interface and the interdiffused layer, reveal the interdiffused performance of alloy elements at elevated temperature, and analyze the structure and composition of the precipitated phases. Moreover, the tensile strength of welding line with the two different techniques and various welding parameters were carried out.The results of explosive welding specimen show that the interfaces formed by explosive welding present disciplinary and consecutive shape. There are no distinctiness diffused layers on the interfaces. After elevated temperature annealing, the interdiffused layers formed in interface of Nb-1Zr and stainless steel. In the interdiffused layer the diffused length of Nb-1Zr alloy elements is longer than that of stainless steel elements, the diffused length of Ni is the longest. There are a mass of needle shape precipitated phases in the interdiffused layers formed by 1300℃ annealing, which are determined to be a metastable cph -(Nb,Ni) by SADP method.The researches of vacuum electron beam self-material brazing specimen find that element interdiffusions are strongly occurred in interface and some new phases are precipitated during welding. The interdiffusion process is likely approached to Nb atoms diffusing into stainless steel side according to the analysis of the morphology and EDS of the interdiffused layer. The precipitated phase is full laminated by two kinds of precipitated phase (white and black laminations). Accordingly, it may conclude that the two full laminated precipitated phases are μ-Fe (Ni) 7 Nb6 and σ -FeCr metallic compounds respectively by the determination of SADP.It is proved by the intensity experiment of welding line that the welds of these two materials using explosive welding and vacuum electron beam self-material brazing are tolerable, nevertheless the welding technique could be improved basing on the study of microstructure of the joint layer.