| Near ? titanium alloys has a broad application prospect in aerospace and other fields due to its high specific strength.However,the high production cost and poor strong plasticity matching limit the further application of near ? titanium alloys.As a result,low cost and improved strong plasticity matching have become a hot topic of research in this type of alloy.In this paper,a new low cost near ? titanium alloy was designed,and the influence of heat treatment process on the evolution of precipitation phase and tensile properties of the alloy were investigated to reveal the relationship between the precipitation phase size and strength and plasticity of the alloy,in order to provide reference for the industrial application of the near ? titanium alloy and the development of heat treatment process.A new high-strength near ? titanium alloy,Ti-6Mo-5V-3Al-2Fe-2Zr(wt.%),was designed using d-electron theory and the molybdenum equivalent criterion based on the low-costing composition setting,and the phase transition temperature of the alloy was measured to be 855°C ± 5°C.After direct aging treatment at different time and temperature,it is found that the secondary ? phase precipitates on the ? matrix of the alloy whose microstructure is all ? phase.The size and spacing of the secondary ? phase as well as the strength and plasticity of the alloy changed slightly when the aging time is extended.As the aging temperature increased,the size and spacing of the secondary ? phase as well as the strength and plasticity of the alloy changed significantly.After aging at 600°C/8h,the strength of the alloy is the highest,the ultimate tensile strength is 1393 MPa,the yield strength is 1303 MPa,and the elongation is 5.9%.After solid solution treatment at different temperatures,it was found that when the temperature was lower than the phase change point,the primary ? phase appeared in the alloy and its number and size changed with the change of the solid solution temperature.When the temperature increases to the ? phase region,the microstructure of the alloy is only composed of ? phase,and the strength of the alloy decreases with the increase of temperature.After solid solution treatment at different temperatures and aging treatment with the same process,it was found that with the increase of solid solution temperature the secondary ? phase spacing in the aging state increased,the strength of the alloy decreased and the elongation after fracture increased.After solid solution aging at 870°C/0.5h + 600°C/8h,the alloy showed a relatively good strength-plasticity match with an ultimate tensile strength of1197 MPa,a yield strength of 1104 MPa and an elongation of 6.7%.The relationship between the organisational characteristics and the strength after aging was analysed,and the influence of the secondary ? phase spacing on the strength was quantitatively investigated,with the increase of the secondary ? phase spacing,the strength decreased,and the change of the secondary ? phase spacing played a major role in the change of the alloy strength after solid solution aging. |
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