Study On Microstructure And Properties Of Heat Treatment Of Ti-22Al-25Nb At Different Temperatures For Spot Forging Laser Forming

Ti₂AlNb based alloy is a new generation of high-strength,high-toughness,oxidation resistance and creep-resistant high-temperature structural materials formed by adding high Nb content on the basis of Ti₃Al-based alloy,and has been widely used in aerospace fields such as engines and aircraft skins.Additive manufacturing has the advantages of high energy density,fast cooling and moldless processing,and has unique advantages in the preparation of difficult-to-deform,high-melting Ti₂AlNb alloys.However,additive manufacturing,as a layer-by-layer melting and stacking process,has a very high solidification temperature gradient,and its microstructure is usually a coarse epitaxial columnar crystal that runs through multiple deposits,which has poor mechanical properties and presents anisotropy,which seriously reduces the mechanical properties of Ti₂AlNb alloy forming specimens and the application range in the aerospace industry.In this paper,the effect of point forging process on the microstructure and mechanical properties of traditional laser deposition Ti₂AlNb alloy was studied,and two sets of Ti₂AlNb alloy samples were prepared by optimizing laser and forging process parameters.The microstructure and mechanical properties of the corresponding two groups of samples were characterized in detail by OM,SEM,tensile experiment,hardness test and other methods.The results show that by alternating point forging and laser deposition,the coarse epitaxial column of the original laser deposition specimen along the deposition direction is successfully removed,and the uniform and fine equiaxed crystals become the main microstructure.Due to the microstructure refinement to reduce the deformation inhomogeneity and slip path,the spot forging laser deposition specimen is greatly improved compared with the conventional laser deposition.The prepared two groups of specimens were subjected to the same heat treatment to analyze the effects of different heat treatment systems on the microstructure and mechanical properties of point forging laser forming Ti₂AlNb alloy and laser rapid forming Ti₂AlNb alloy,when the two process specimens were treated with solid solution,their tensile strength decreased and plasticity was greatly improved,which was due to grain boundaries,the volume fraction of the precipitated phase in the crystal decreased,and the slip resistance of the dislocation and the position of crack nucleation were reduced.Correspondingly,after the aging treatment of the solution sample,a large number of secondary O phase precipitation provided the dislocation slip resistance and crack initiation position,and the tensile strength increased significantly and the plasticity decreased.Under the same heat treatment system,the mechanical properties and microhardness of Ti₂AlNb formed by point forging laser are better than those of laser rapid forming Ti₂AlNb alloy.