Ti65合金饼坯锻件持久性能及位错演变规律研究

Study on Dislocation Evolution and Stress Rupture Properties of Ti65 Alloy Billet Forging

采用光学显微镜、电子背散射衍射和透射电子显微镜等研究了大厚截面的Ti65合金饼坯锻件力学性能以及在650℃/240 MPa条件下不同位置和同一位置不同持久时间停机后的位错演变规律。结果表明:大厚截面的锻件从边缘到心部的拉伸和持久性能存在较大差异,当距表面距离从0 mm增加至30 mm(锻件厚度的1/4)时,室温和650℃抗拉强度分别从1203 MPa和704 MPa降低至1081 MPa和652 MPa,持久断裂时间从66 h提升到161 h;当距表面距离从30 mm增加至60 mm(锻件厚度的1/2)时,抗拉强度和持久性能基本保持不变。从持久初期至持久后期,可以发现等轴α相与片状α相中的位错密度均显著升高,高密度的位错主要集中于片状α相界面处。大应力持久条件下位错可以直接穿过硅化物,厚片层α相内部弥散分布的α2相有利于持久性能的提升。

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 equiaxedαphase and lamellarαphase both significantly increases,and high-density dislocations are mainly concentrated in the interface of lamellarαphase.Under high stress conditions,dislocations can directly penetrate the silicide,thick lamellarαphase internally dispersed distribution ofα2 phase is beneficial for stress rupture properties.