Study On Microstructure And Properties Of Zr-Sn-Nb Zirconium Alloy Welding

Zirconium alloy was widely used in the nuclear reactor as the important structural with excellent mechanical and corrosion properties under operational conditions and low neutron absorption,and the weld is a necessary process to conect all parts After welded, the microstructure of welded joint has been greatly changed. Therefore, it is very important that explored the change rule between microstructure and properties of zirconium alloy welded joint to promote the application of zirconium alloy welded structure in nuclear reactorFirstly, for the high temperature chemical properties of zirconium alloy,considered the steam flow in the welding process will impact the shielding air flow, and there is a linear relationship between the strength of steam flow and the heat input. By comparing the effect between gas flow application form 、gas flow rate on and the protective effect of welded joint. Investigated whether the gas protection form can achieve the required environmental of the zirconium alloy welding. The results show that use the axial、side、back blowing protection can ensure the welding environment of zirconium alloy, and under P=1400 V=60mm/s, the gas flow rate in 15~20L/min can provide a better welding environmental. In the selected welding parameters(P=1350~1500W, V=55~75mm/s), the higher laser power and the slower welding speed can reduce the effect of air flow protection, then increase the gas flow rate can enhance the anti-interference ability of the gas flow.Secondly, This paper carry out the exploration that between welding parameters and the mechanical properties and the microstructure of zi rconium alloy. Based on the analysis of the grain size, grain orientation, grain boundary angle difference and joint composition. investigated the mechanism which the welding joint microstructure effect on mechanical properties. Based on the corrosion resi stance and microstructure has certain relevance, evalued zirconium alloy corrosion resistance under the welding conditions. the laser power should be controlled at P=1350W~1400W, The welding speed should be controlled at V=60mm/s~65mm/s. And heat treatment must be carried out after welding, its main purpose is to eliminate the β phase in the welded joints.Finally, this paper base on the first principle calculation, deduced the most probable position of Nb element in the Zr(Nb,Fe) 2 with hexagonal structure and obtained the optimal atom occupation model. Calculated the thermodynamic properties of β-Zr、β-Zr(Nb)、β-Nb 和 Zr(Nb,Fe)2 at the high temperature. The result show that the solid solution of Nb element in β-Zr can greatly improved the structural stability of the β-Zr. That is the reason why β-Zr with rice Nb can left at the room temperature. By calculated the effect of the Nb element supersaturated in α-Zr on the intrinsic mechanical properties, found that the Nb element supersaturated can reduce the structural stability of α-Zr. Further compared the elastic modulus of Nb supersaturated, found the G/B is less than 0.5 and the shear modulus G value has a little increased, According to the relationship between G/B, G and the mechanical properties of materials,the Nb supersaturated can lead the ductile α-Zr to brittleness and increased the hardness of α-Zr, that is one of the reasons that the hardness of weld joint is higher then the base material. And the influence of different welding parameters on the hardness of welded joint is mainly due to the strength value of the residual stress in the joint.