Near-Net Shaping And Mechanical Property Control Of Thin-Walled Complex Titanium Alloy Parts By Powder Hot Isostatic Pressing

Titanium alloy powder hot isostatic pressing near-net shaping(NNS-HIP)process can realize the overall forming of large-size and complex components,and has important research value and application prospects in the fields of aviation and aerospace.In this study,a systematic study was organized at the two key technologies of alloy performance reconciliation and component dimensional control in the NNS-HIP process of complex thin-walled titanium alloy components.The main research contents and conclusions are as follows:The low-oxygen TA15 alloy electrode prepared by the melting and casting method was used to study the powder preparation technology suitable for NNS-HIP process.Results show that after sieving with a 100-mesh sieve,the tap density of EIGA powder is higher,reaching 3.02 g/cm3,and the plasticity of EIGA alloy is slightly higher after HIP compared with the EIGA powder.While PREP powder has a coarser particle size,better sphericity,lower cost and fluidity of 25 s/50g.The densification mechanism and trend of microstructure transformation of alloy powder at different HIP temperatures were further studied.Results show that the densification of the powder is basically completed at 850?.A "baske weave structure" composed of lath clusters and small equiaxed crystals around lath clusters is formed below 950?.When the temperature is above 950?,the alloy transforms into Widmanstatite structure gradually,and the grain size grows with the increase of HIP temperature.The strength and elongation show a decreasing trend with the increase of HIP temperature,from 948 MPa and 17.3%for the 910? alloy specimens to 864 MPa and 11.6%for the 950? specimens.The specimens below 950? tend to form holes from the equiaxed crystal area at the edge of the original grains,and micro-pore aggregation appears along the ? phase in the lath structure.By performing "near-beta phase powder HIP" at 950 ?,a fine-grained "Widmanite structure" can be obtained,so the fracture toughness increased from 82 MPa(?)of the 910? specimen to 115 MPa(?)for the 950? specimen through the toughening of the composite structure,which is 29%higher than that of conventional forged alloys.A finite element model for the powder HIP was established,and the shrinkage deformation trend of the round complex thin-walled powder component during HIP was analyzed through numerical simulation.The results show that structure of the capsule has a great impact on the dimention and quality of the components that formed.The two ends of the component and the edge of the lumen boss are affected by the "corner effect",forming a low-density zone.The inner cavity boss has a "size effect" on the shrinkage of the outer surface,that is,large boss structure easily causes the outer surface to dent,which is not conducive to size control and material utilization.This phenomenon has been verified in actual testing of component.An experimental method for forming simulation and result verification is established through the finite element numerical simulation and "three-dimensional scanning" of the forming component.The result shows that the simulation result can be fully and accurately verified by the simulation result " 3D reconstruction" and the simulation result-measured result "best fit".The dimensional shrinkage and deformation of thin-walled titanium alloy component during powder HIP as well as the mechanical properties of the component were studied.The results show that by adopting a "rigid-flexible coupling" capsule structure to form the deep-cavity thin-walled cylindrical components,the densification of the component is realized through the inward shrinkage and deformation of the outer wall.The size deviation of the inner cavity profile is less than 0.1 mm,and the wall thickness linear shrinkage rate is between 42%-45%.The capsule structure has a great influence on the dimensional deformation of powder HIPed component.The corner structure hinders the deformation and affects the uniformity of the component shrinkage,while large plane structure has less restriction on the shrinkage of the components,so the shrinkage rate is higher.For areas with partial suspension features on the component,due to the action of gravity under high temperature,the sagging deformation occurs.Sampling and analyse were carried out on the thin-walled component.The results show that the component subjected to HIP at 930? is"basket weave structure",and the microstructure in different thicknesses and sampling directions is basically the same.The tensile strength,yield strength and elongation of the alloy in the component are 928 MPa-938 MPa,850 MPa-869 MPa and 12.3%-15.5%respectively,and the fluctuation of mechanical performance is small.This process is expected to be applied to cabin-like thin-walled components in the fields of aviation,aerospace and armored weapon.