Study On Creep And Hot Workability Of Rare Earth Microalloying Titanium Alloy Material

Titanium alloys are widely used in the fields of aerospace and marine vessels due to their high specific strength and corrosion resistance.With the continuous development of modern equipment in the direction of high performance,long life and high reliability,titanium alloy materials.The service performance such as creep resistance puts forward higher and higher requirements.Therefore,research on titanium alloy materials with better creep resistance is an urgent need in the fields of aerospace and ocean.Based on the service conditions of titanium alloys in aircraft and ocean submersibles,this paper conducts experimental research on high-temperature tensile creep and room-temperature compression creep of rare-earth modified titanium alloy materials.At the same time,the high temperature hot workability of the alloy is systematically studied to provide basic theoretical support for the design of titanium alloy materials with more excellent creep resistance.The main research work is as follows:First,four kinds of titanium alloy materials with different silicon and scandium contents were prepared by VAR smelting,and tensile creep experiments under 400?and 200MPa conditions were carried out.The results show that the creep strains of TC4-0.25Si,TC4-0.3Sc and TC4-0.25Si-0.3Sc alloys are reduced by 48.3%,11.4%and 50.6%,respectively,compared with TC4 alloy;the steady-state creep rate of TC4-0.25Si,TC4-0.3Sc and TC4-0.25Si-0.3Sc alloys are 50.7%,4.6%and 57.5%smaller than TC4 alloys.It shows that both Si and Sc can improve the creep resistance of titanium alloys,and Si can significantly improve the creep resistance of the alloys.Using microscopic characterization methods to observe the material,the analysis found that silicon and scandium have a fine-grain strengthening effect on the alloy,which can increase the room temperature and high temperature strength of the titanium alloy,but silicon is unfavorable to the room temperature plasticity of the alloy.Silicon significantly improves the high temperature tensile creep resistance of the alloy,which is mainly due to the solid solution strengthening and the hindering effect of the silicide on the dislocation movement during the creep process.The Sc₂O₃formed by the combination of rare earth scandium and oxygen in the matrix can purify the matrix and have a softening effect on the alloy.The formation of horseshoe-shaped Al₃Sc precipitates helps to improve the creep properties of titanium alloys.In addition,the Sc solid-dissolved in the matrix can inhibit the precipitation of silicide and promote the formation of?₂ phase,which helps to improve the high temperature creep resistance of titanium alloys.Secondly,a compression creep experiment was performed on the material after solution aging at room temperature and a stress of 0.9?_0.2.The results showed that the creep strains of TC4-0.25Si,TC4-0.3Sc and TC4-0.25Si-0.3Sc alloys were reduced by23.1%,53.3%and 46.7%respectively compared with TC4 alloy;the steady-state creep rate of TC4-0.25Si,compared with TC4,TC4-0.3Sc and TC4-0.25Si-0.3Sc alloys are reduced by 20.9%,47.75%and 53.15%,respectively.It shows that both silicon and scandium can improve the room temperature compression creep resistance of titanium alloys,and the effect of scandium is better.The compression creep experiment of the material shows typical characteristics of the creep curve,that is,the creep deceleration phase and the creep steady-state phase,which conform to the power law equation.With the help of TEM characterization and analysis of the alloy creep deformation mechanism,it is found that the main deformation mechanism of the alloy room temperature compression creep is the slip of dislocations and a small amount of twinning.The addition of silicon can inhibit the formation of twins during the creep process,while scandium can purify the matrix,reduce the concentration of interstitial atoms in the alloy,and promote the formation of twins during the creep process.Finally,the annealed material is subjected to a thermal compression experiment at 800-950?,0.01-10 s^-1,and the power dissipation diagram,instability diagram and thermal processing diagram of the alloy are obtained by analyzing and calculating the thermal compression experimental data.The study found that:TC4,TC4-0.25Si,TC4-0.3Sc and TC4-0.25Si-0.3Sc alloy thermal deformation activation energy are497.65 kj/mol,485.6 kj/mol,549.13 kj/mol and 494.98 kj/mol,respectively.Silicon reduces the thermal deformation activation energy of the alloy,and scandium can increase the thermal deformation activation energy of the alloy.Rare earth scandium makes the hot deformation structure smaller and reduces the hot working window of the alloy,while silicon can expand the hot working window of the titanium alloy and improve the hot working performance of the alloy.At the same time,silicon can promote the formation of?phase during thermal deformation.