Ti-23Al-17Nb合金双态组织的控制及其对力学性能的影响

Control of Duplex-Microstructure and Its Effect on Mechanical Properties of Ti-23Al-17Nb Alloys

研究Ti-23Al-17Nb(at%,下同)合金在不同热处理条件下形成的双态组织的微观细节特征及其形成规律,分析双态组织细节特征对力学性能的影响,探讨综合改善合金拉伸性能和高温持久性能的途径。结果表明,经α2+B2两相区温度变形的该合金,通过固溶处理/连续冷却和固溶快冷+时效两种方式的热处理均可形成双态组织。其中固溶快冷+时效方式可以实现O相板条数量、尺寸、分布及排列更有效的控制,时效温度的降低有助于板条的细化和混乱排列。在α2相等轴颗粒形貌及体积分数基本一致(约15%～20%)的情况下,O相板条体积分数的增加有利于合金高温持久性能的显著提高,但会造成合金室温拉伸延伸率的下降;O相板条的细化有利于合金室温和高温拉伸性能的同时改善,但使高温持久性能有所降低;通过1060℃固溶处理/油淬+850℃时效处理获得的双态组织具有强度、塑性和高温长时性能的最好匹配。

The detailed microstructure characteristics and the formation regulation of the duplex microstructure of Ti-23Al-17Nb （at%） alloys under different heat treatment conditions were studied. The effects of detailed microstructure characteristics on the mechanical properties of alloys were also investigated. The approaches to improve the both tensile and endurance properties at elevated temperature were discussed. The results indicate that for the alloys forged in （a2＋B2） phase field, the duplex microstructure can be obtained either by treatment of solution in （a2＋B2） field and oil quenching plus aging in （aE＋B2＋O） field. The volume fraction, size and distribution pattern of O phase laths can be controlled well. The relatively lower aging temperature is of benefit to form the finer and more random distribution of O phase laths. Increasing the volume fractions of O phase laths can improve the endurance properties at elevated temperature but decrease the room-temperature elongation in the case of similar sizes and same percent content （15%-20%） as equiaxed a2 particles, while the finer sizes of O phase laths can increase the tensile properties both at room and elevated temperatures, but decrease the endurance properties. The optimum matching of tensile strength, elongation and endurance properties of the alloys at elevated temperature can be obtained by the heat treatment of 1060 ℃ solution and oil quenching plus 850 ℃ aging.