Study on Dislocation Evolution and Stress Rupture Properties of Ti65 Alloy Billet Forging
The optical microscope,electron backscattered diffraction and transmission electron microscopy were employed to investigate the mechanical properties and dislocation evolution under stress rupture test(650℃/240 Mpa)of Ti65 alloy billet forging with large thick section.The results indicate that the tensile and stress rupture properties of the forging with large thick section are highly dispersed from the edge to the center.As the distance from the surface increases from 0 mm to 30 mm(1/4 of forging thickness),the room temperature and 650℃tensile strengths of Ti65 alloy billet forging decrease from 1203 Mpa to 1081 Mpa and 704 Mpa to 652 Mpa respectively,the stress rupture time increases from 66 h to 161 h.As the distance increases from 30 mm to 60 mm(1/2 of forging thickness),the tensile strength and stress rupture properties remain unchanged.From the initial stage of persistence to the later stage of stress rupture,the dislocation density of equiaxed α phase and lamellar α phase both significantly increases,and high-density dislocations are mainly concentrated in the interface of lamellar α phase.Under high stress conditions,dislocations can directly penetrate the silicide,thick lamellar α phase internally dispersed distribution of α2 phase is beneficial for stress rupture properties.
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