Study On Rotary Friction Welding Technology And Joint Structure Properties Of Molybdenum

Molybdenum has the advantages of high melting point,small neutron absorption cross section,good high temperature strength,small linear expansion coefficient and corrosion resistance.The nuclear fuel cladding made of molybdenum can resist severe accident conditions for a long time,it will help people have enough time to take emergency measures.After installing the fuel pellet and the hollow upper end plug,the nuclear fuel cladding prepared with molybdenum needs to weld the upper end plug and the rod-shaped molybdenum seal block together under a high-pressure environment.However,due to the large size of the weld seam and the heat-affected zone after the fusion welding of molybdenum and the severe coarsening of the grains,the strength and toughness of the molybdenum-clad welded joints are very poor,and the weld penetration in the high-pressure environment is significantly reduced.The rotary friction welding method is a solid-phase welding method.The material does not melt and the temperature is low during welding.Compared with the fusion welding method,rotary friction welding has the advantage that the welding quality is hardly affected by environmental pressure.Compared with the friction stir welding method,rotary friction is the friction between two molybdenum workpieces,and there is no problem that the tools are easy to wear.Therefore,the rotary friction welding method is very suitable for mass welding of molybdenum shells under different environmental pressures.The final stage of most rotary friction welding requires the application of a large momentary axial upset load,which usually helps to obtain a clean,dense,high quality joint.However,for the slender molybdenum fuel cladding assembly with poor rigidity,the instant axial upset load cannot be applied in the final stage of welding.In order to study that the welding quality can still be obtained under the condition of no axial upset load,this paper carried out a molybdenum no upset rotary friction welding test in the atmospheric environment,and studied the welding time to the joint morphology and axial shortening.Influence of microstructure,microstructure,microhardness,tensile strength and tensile fracture morphology.At the same time,a two-dimensional axisymmetric thermo-mechanical coupling model based on Abaqus finite element software is established on the basis of experiments,and the influence of the rotational friction welding process parameters on the temperature field and interface pressure distribution of the friction contact surface of the joint is calculated and studied.In the experiment,the frictional contact position of the molybdenum rotary friction welding process burned very violently,and the flash was thrown out of stability,showing a "spiral" shape;the axial shortening of the molybdenum rotary friction welding joint increased linearly with the increase of the welding time;The weld zone of the friction welded joint is significantly refined near the radial center,and the weld zone is not oxidized during the welding process;as the welding time gradually increases from 2s to 5s,the tensile strength of the molybdenum rotary friction welded joint increases first and then decreases Small,when the welding time is 4s,the maximum tensile strength is 477.34 MPa,which can reach 78.66% of the strength of the base material;through finite element simulation,it can be found that when the welding process enters a stable stage,the peak temperature range is about the distance from the friction contact surface.In the range of 1/2-2/3 toward the center;compared with the welding speed,changing the welding pressure and welding time has a greater impact on the joint temperature field and interface pressure distribution.Research results show that it is feasible to weld the upper plug sealing joints of molybdenum fuel cladding components by non-top forging rotary friction welding.The research results have practical guiding significance for solving the welding bottleneck problems encountered in the development of accident-tolerant nuclear fuel technology in China.