Study On Strengthening And Toughening Technology Of TB8 Titanium Alloy

In this paper,the high strength TB8 titanium alloy was investigated.The new technology such as pre-aging,normal aging,double aging were introduced in order to study the change of the alloy on microstructure and room mechanical properties in different process.A pre-aging process was proposed for the low superplasticity of TB8titanium alloy.The homogeneously dispersed second phase was precipitated to optimize the pre-deformation microstructure and improve the superplasticity.When using cold heading forming high strength bolt fasteners,the alloy still maintains good plasticity while retaining the strengthening effect of cold deformation by low temperature aging technology.So it can provide relevant technical parameters and experimental basis for the cold heading forming of TB8 titanium alloy bolt fasteners.The effect of different aging techniques on the microstructure and mechanical properties of the TB8 titanium alloy after solution treatment was investigated by pre-aging,normal aging and double aging.The results show that the transformation of???occurred in pre-aging treatment?350??1h/410??1h?,the final microstructure of the alloy was??10??;And the microstructure of the alloy after normal aging treatment?500??8h/520??8h?was??10??phase;Combined with pre-aging and normal aging?350??1h+520??8h/410??1h+520??8h?process,fine lamellar?phase appear in both intragranular and grain boundaries.With the aid of secondary nucleation effect of?phase,a finely dispersed?phase can be obtained in TB8titanium alloy by using double aging technology?410??1h+520??8h?.Thus achieving a comprehensive mechanical properties with tensile strength of 1350MPa and elongation of 16.5%.The pre-aging treatment of TB8 titanium alloy with different parameters was performed before superplastic elongation.The effects of pre-aging techniques on microstructure,elongation,and the fracture structure after stretching were studied.The results show that the pre-aging temperature mainly affect the content and morphology of?phase,while the pre-aging time mainly affect the size of supersaturated?phase and the particle size of the desolvable phase in TB8 titanium alloy.The pre-aged samples all undergo dynamic recrystallization in varying degrees during stretching.When TB8 titanium alloy obtains the best superplasticity,the corresponding pre-ageing process parameter is 520?for 1 hour.The elongation is 362%,higher than the stretching parameter of 840??10^-4s^-1,it improves the superplastic forming efficiency.The key of high strength bolt fasteners to obtain better performance was combining cold upsetting deformation with proper heat treatment technology.The effect of low temperature aging technique at different temperatures and times on microstructure and hardness of TB8 titanium alloy were studied.The microstructure of the alloy is still a single?phase after treated at a low temperature of 320?.When temperature rises to 350?,a significant phase transformation occurs in the alloy,the XRD and DSC analysis show that the???phase transformation occurs at this temperature.The holding time mainly affect the quantity and size of the precipitated phases,when the holding time increases from 0.5h to 1h at 350?,the size of precipitated?phase grows up.TB8 titanium alloy cold heading fasteners have better comprehensive performance because?phase can provide nucleation sites for subsequent?phase precipitation to refine grains at a low temperature aging condition.