Research On Micostructure Evoliton Of Ti-6Al-4V Alloy Additively Manufactured By Electron Beam Melting And Annealing

Electron beam additive manufacturing has the advantages of high speed,low cost,no material limitation and suitable for processing parts of various shapes.Titanium alloy has the advantages of high strength,excellent corrosion resistance and good low temperature toughness,but when forming complex structure,the material utilization rate is low,the cycle is long and the manufacturing cost is high,which has formed certain restrictions on the practical application of titanium alloy in the field.Electron beam additive manufacturing is superior to other titanium alloys.However,due to the influence of the uneven microstructure on the mechanical properties of the deposition state of titanium alloy formed by electron beam additive manufacturing,there is a certain gap between it and the traditional forging process.The uniform microstructure and mechanical properties of titanium alloy can be improved by post heat treatment of additive.The main contents of this study are as follows: through the analysis of the additive manufacturing process of TC4,the columnar crystal formation,block structure evolution process and martensite phase transition in the additive manufacturing process are studied,and the phase transition process of TC4 molding in additive manufacturing is analyzed.By analyzing the microstructure and properties of additive manufacturing TC4 after heat treatment,the microstructure,microstructure change,phase change type,hardness,tensile strength,elongation and fracture morphology of materials before and after heat treatment were studied,and the relationship between microstructure,hardness,fracture behavior,tensile property and temperature change after heat treatment of additive manufacturing TC4 was analyzed.The results show that:(1)after electron beam increase of deposition state TC4 sample made in material is given priority to with ɑ phase,and contains a small amount of beta phase.(2)material in the manufacturing process,have ɑ ’phase,the process is a diffusion phase transition,ɑ ’ phase for ɑ phase of supersaturated solid solution.(3)in thedeposition process,the massive structure is formed by the short-range diffusion phase transition,which has no fixed shape and appears randomly.The phase transition temperature is between the initial temperature of martensite phase transition and the long-range diffusion phase transition.(4)with the increase of annealing temperature,the fusion line disappears,and the oversolid solution unstable phase in the block structure precipitates out and turns into a more uniform basket structure.(5)when the annealing temperature is more than two titanium alloy phase transition temperature of 880.1 ℃,the histogenesis and isomer and recrystallization.The microstructure coarsened when the annealing temperature increased.(6)with the increase of annealing temperature,the fracture form of the tensile specimen in the direction of deposition changed from ductile fracture to brittle fracture,and the strength decreased,and the plasticity first increased significantly and then decreased.(7)annealing temperature affects the hardness of material uniformity,deposition and annealing temperature is 700 ℃ and 900 ℃ specimen hardness have good uniformity.