Study On The Dissimilar Joints Of Taand GH3128 Welded By Electron Beam Welding

Ta is a kind of representative refractory metal with excellent thermophysical properties,which is often applied in high-temperature structural materials such as missiles,nuclear power construction and aero-engines.GH3128,a solid solution strengthening superalloy,is ideally suited for aero-engine combustion chambers and intermediate heat exchangers.With the increasing demand for engine performance in aviation,the heterogeneous combination of these two materials can not only optimize the structural design,but also lower the cost.High-speed electron beam is used as heat source to collide on the surface of the material by electron beam welding.The material is rapidly melted and solidified by converting the kinetic energy of the electrons into heat energy.It can not only adjust the beam and preciously control the heat input to control the melting amount of the two base materials,but also effectively reduce the metallurgical reaction time by controlling the welding speed and thus control the metallurgical reaction process.Therefore,electron beam welding is the better choice to achieve a reliable connection between Ta and GH3128.In this paper,electron beam welding is carried out between Ta and GH3128,and the problems existing in the central welding of the two metals are analyzed.The effects of central welding and partial beam welding on the microstructure and mechanical properties of the joint are studied and then the joint is annealed and solution treated in an innovative way.The microstructure of the joint is analyzed using a super depth-of-field microscope,a scanning electron microscope and a XRD diffractometer;their mechanical properties are evaluated by microhardness and tensile tests.The central welding tests of Ta and GH3128 show that during central welding,the problems of pores and penetrating cracks are conspicuous,a large number of tantalum nickel and tantalum chromium intermetallic compounds are precipitated in the molten pool and the weld has low plasticity.When the beam is 0.2mm deflected to the Ta side,theamount of melting Ta is increased and the weld is chiefly composed of equiaxed and columnar grains.The hardness distribution in the molten pool is more uniform than that during central welding and the hardness of the joint increases as the amount of melting Ta increases.For these reasons,welding with 0.5mm beam offset to Ta is applied to realize the connection between Ta and GH3128.At this time,the weld is mainly equiaxed grains and the grain refining further improves the hardness and strengthen of the joint.Considering that the intermetallic compounds layer between Ta and molten pool can't be eliminated by partial beam welding,the presence of these compounds will cause stress concentration in the molten pool.In order to further enhance the strength of the joint,annealing treatment and solution treatment are innovatively used in this paper.After annealing treatment,the composition of the molten pool becomes more uniform,the stress concentration is alleviated to a certain extent and the hardness and strength of the joint are improved.However,a large number of needle-like ? phases exist in the molten pool after annealing treatment,which indicates that the brittle fracture characteristics of the joint don't be improved.Thus,the welded joint is subsequently subjected to a solution treatment at 1180? for 1h.It is found that the segregation of each element in the molten pool is significantly reduced after solution treatment,a large amount of Ta is dissolved into the GH3128 matrix and the mechanical properties of the joint are greatly improved due to the effect of solution strengthening.A small number of dimples appear at the fracture,suggesting that the brittleness of the joint is slightly improved.