| TC4 titanium alloy multi-cavity structural parts were made by diffusion welding.The combination of the excellent comprehensive properties of titanium alloys such as low density and high specific strength and the lightweight design of multi-cavity structural parts can simultaneously meet the requirements of aerospace,automobile manufacturing for lightweight and high performance.However,the contradiction between the welding deformation and the joint strength produced by the diffusion welding process is not conducive to the accurate manufacture of multi-cavity structural parts.In order to solve the contradiction between welding deformation and strength and realize the precise manufacture of multi-cavity structure,this paper simplifies the design of TC4 titanium alloy multi-cavity structure according to the structural characteristics of aero-engine intake casing.Using ABAQUS finite element simulation software,the diffusion welding process of TC4 titanium alloy multi-cavity structural parts was simulated,and the welding temperature field,stress field and cavity deformation were analyzed.The effect of local deformation of the cavity and the weld rate of the joint optimizes the design of the weld surface.The diffusion brazing process of TC4 titanium alloy was studied,and the application prospect of brazing process in the main bearing parts of aero-engine was explored.The main conclusions of this paper are summarized as follows:On the basis of the orthogonal experiment of TC4 titanium alloy,the influence of welding process parameters on the microstructure and properties of titanium alloy diffusion welded joint was analyzed with the voids,tensile strength and primary α volume ratio of the diffusion welded joint as indicators,and the optimization of TC4 titanium alloy was carried out.Research shows:Under the optimized process parameters（870℃,5MPa,and 120min）,there are no unclosed voids in the welding interface of the joint,the tensile strength is 977.42MPa,which is 97.85%of the tensile strength of the base metal,and the primary αvolume ratio is 52.74%.Within the selected welding process parameters,the effect of process parameters on the welding interface void closure,joint tensile strength and primary α volume ratio is welding temperature>holding time>welding pressure.the welding rate,the primary a volume ratio,and the plasticity of the joints are improve with the increasing of the welding temperature,welding pressure,and holding time.However,the welding temperature is too high and the holding time is too long,which makes the grain of the joint coarsen,resulting in a decrease in the tensile strength.Based on the process parameters optimized by the orthogonal experiment of TC4 titanium alloy,the ABAQUS finite element numerical simulation software was used to simulate the diffusion welding process of the multi-cavity structure of TC4 titanium alloy with two welding sections,and the welding section was optimized.Combined with the basic test,the deformation trend of the cavity was analyzed,and the accuracy of the simulation analysis was verified.By comparing the local deformation of the cavity and the welding rate of the joint for two different welding surfaces,the design of the welding surface was optimized.Research shows:The temperature and stress at the inner and outer side walls of the cavity of the multi-cavity structural part without hollow are significantly higher than other parts;At the cavity,the higher stress distributed at the hollow structure is beneficial to promote the plastic deformation of the welding interface,the interface diffusion and reduce the welding deformation of the cavity.During the diffusion welding process of multi-cavity structural parts,the upper and lower middle parts of the cavity show a convex deformation trend,and with the increase of the overall welding deformation rate,this deformation trend becomes more and more obvious.The hollow structure of the multi-cavity structure with hollow reduces the stress value of the cavity and the local welding deformation,and increases the local plastic deformation at the welding interface,which is beneficial to promote interface diffusion and hole closure.According to the joint welding rate of metallographic testing and ultrasonic testing,the welding rate of multi-cavity structural parts welded joints increases with the increase of the overall welding deformation rate.Under the same overall welding deformation rate,the joint welding rate of multi-cavity structural parts with hollow is significantly higher than that of multi-cavity structural parts without hollow.The hollow structure reduces the local welding deformation at the cavity,increases the plastic deformation of the welding surface,promotes the diffusion of atoms near the welding interface and the closure of holes,and improves the welding rate of the joint,which is an optimized welding section design.When the optimized welding process parameters are used and the overall control deformation rate is 5%,the welding rates of the two different welding surfaces are～95%and～98%respectively,which meet the design requirements of the welding rate.The local welding deformation rate of the cavity part of the cavity structure is～1.98%,which is significantly lower than the local welding deformation rate of the cavity part of the multi-cavity structure without hollow（～4.74%）.The effect of holding time on brazing microstructure and properties and high cycle fatigue properties of brazed joints were analyzed by using Ti-18Zr-15Cu-10Ni（wt.%）filler.Research shows:The weld width and the primary a volume ratio of the joint increased with the prolongation of the holding time,but the weld structure consisted of coarse acicular α Ti,（Ti/Zr）2（Cu/Ni）IMCs,residual β Ti,and eutectoid α Ti.During the brazing process,solder melting,isothermal solidification,and eutectoid decomposition occur.Among them,when the temperature is lowered to the β-trans-temperature,α Ti nucleates and grows from the equiaxedα Ti grain boundary with the highest energy,and grows dendritic to the inside of the weld,resulting in the enrichment of Al in the growing α Ti,part of the Cu and Ni atoms are precipitated and accumulated in the residual β Ti,and the enriched Cu and Ni induce the residual βrich Ti to undergo eutectoid decomposition of βrich Ti→Ti2Cu+α Ti,which makes the weld seam still form（Ti/Zr）2（Cu/Ni）IMCs when the holding time is longer.The tensile strength of diffusion brazed joints first increased with the prolongation of holding time,and reached the highest value of 984.90 MPa at 60 min.When the holding time continued to extend,the tensile strength decreased.The elongation of the joint after breaking increases with the prolongation of the holding time,and reaches the highest value of 12.39%at 90 min.The fatigue limit of TC4 titanium alloy brazed joints is 492 MPa.The morphologies of the crack initiation region,the crack propagation region,and the final fracture region are all affected by the fatigue load stress amplitude. |
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