时效温度对一种新型β钛合金组织演变及力学性能的影响

Effect of aging temperature on microstructural evolution and mechanical properties in a novel β titanium alloy

摘要:

采用d-电子合金设计法设计了一种β钛合金,Ti-6Mo-5V-3Al-2Fe(wt.%)。在450℃~600℃范围内选取了多个时效温度进行时效处理,以研究时效温度对该合金组织演变及力学性能的影响。结果表明,当时效温度为500℃时,在ω辅助形核机制作用下,形成了尺寸和相间距更小的次生α相,在此细小的次生α相对β基体的强化作用下合金抗拉强度达到最大值,为1510MPa；同时,由于晶界α相的析出以及晶界无析出区的形成,导致合金的塑性极差,伸长率仅为4.6%。随着时效温度的升高,晶内细小的次生α相粗化。粗大的次生α相导致其相间距增大,并使可有效阻碍位错运动的α/β相界面减小。时效温度的升高使合金强度降低,但合金塑性提高。当时效温度升高至600℃,在β晶界处形成了向晶内平行生长的板条状次生α相,同时β晶粒内次生α相间距增大,使合金塑性明显提高,伸长率可达12.2%。

Abstract:

A β titanium alloy Ti-6Mo-5V-3Al-2Fe(wt.%) was designed in terms of d-electron alloy design method. Aging treatment was performed at various temperatures ranging from 450℃ to 600℃ for 4h to study the effect of aging temperature on microstructure evolution and tensile properties. The results show that the secondary α phase with smaller size and inter-particle spacing formed under ω-assisted nucleation mechanism at the aging temperature of 500℃. The highest ultimate tensile strength of 1510MPa is obtained due to the strengthening of fine acicular secondary α phase within β grain, while poor elongation of 4.6% is found as a result of the inevitable precipitation of α phase at grain boundary and the formation of precipitate free zone near grain boundaries. Fine secondary α precipitates tends to coarsen with the increasing aging temperature. Coarse α precipitates can bring about broad inter-particle spacing and can result in less α/β interfaces that act as effective dislocation barriers. The increase of aging temperature leads to the variation of tensile properties, i.e. the strength decreased while ductility changed in opposite way. A considerable improvement of elongation to 12.2% is achieved by increasing aging temperature to 600℃, in association with the formation of parallel secondary α laths near β grain boundaries and broad inter-particle spacing of secondary α phase within β grains.