Better balance of room and high temperature properties by the microstructure modification for orthorhombic Ti-22A1-20Nb-2W titanium alloy.

近年来，Ti_2AlNb金属间相（有序正交相）基合金因具有高的强度比、良好的加工性能和较高的断裂韧性而受到广泛关注。特别是作者研制的W变质Ti-22 Al-20 Nb-2 W（mol %）合金，表现出上级的蠕变等高温性能。然而，这种合金表现出较差的室温延展性。减小现有的B2（CsCl型有序bcc相）相晶粒尺寸将有利于改善其室温拉伸性能。本研究旨在通过热机械处理细化B2晶粒，即在B2+α_2（有序hcp相）两相区对气体雾化Ti-22 Al-20 Nb-2 W粉末的HIP处理压坯进行热轧，然后在相同的B2+α_2两相区进行退火。热机械处理后B2基体中形成的球形α 2颗粒的分布与退火温度和时间密切相关，由于这些α 2颗粒对晶粒生长的钉扎作用，最终获得了尺寸为27 ~ 108 μm的B2晶粒。B2晶粒尺寸为108 gm的材料的抗拉强度和室温伸长率分别为850 MPa和0.5%，而B2晶粒尺寸为27 gm的材料的抗拉强度和室温伸长率分别为1220 MPa和5%。具有61 μm的B2晶粒尺寸的材料显示出室温拉伸强度（1050 MPa）和伸长率值（3.2%）的更好平衡，而不牺牲高温蠕变性能（稳态蠕变速率：1.0 × 10^<-9>s^<-1>.

Recently, Ti_2AlNb intermetallic phase (ordered orthorhombic phase) base alloys have received much attention for their high strength-to-weight ratio, good workability and greater fracture toughness. Especially, W-modified Ti-22Al-20Nb-2W (mol %) alloy, developed by the authors, shows superior high-temperature properties such as creep. However, this alloy exhibits poor room-temperature ductility. It would be beneficial to reduce the prior B2 (CsCl-type ordered bcc phase) phase grain size to improve its room-temperature tensile properties. This research was therefore aimed to refine the B2 grains using thermo-mechanical processing, in which HIP processed compacts of gas-atomized Ti-22Al-20Nb-2W powder were hot-rolled in the B2+α_2 (ordered hcp phase) two-phase region and subsequently annealed in the same B2+α_2 two-phase region. The distribution of spherical α_2 particles formed in the B2 matrix by this thermo-mechanical treatment was highly dependent on the annealing temperature and time, and due to the pinning effect of these α_2 particles against grain growth, B2 grain sizes ranging from 27 μm to 108 μm were finally obtained. The tensile strength and room temperature elongation of the material with B2 grain size of 108 gm were 850 MPa and 0.5 %, respectively, whereas those of the material with B2 grain size of 27 gm were 1220 MPa and 5 %, respectively. Materials with B2 grain size of 61 μm showed a better balance of room-temperature tensile strength (1050 MPa) and elongation value (3.2 %) without sacrificing high-temperature creep properties (steady-state creep rate : 1.0 x 10^<-9> s^<-1>.