等轴细晶Ti-45Al-7Nb合金的高温机械性能及变形机制

High Temperature Mechanical Properties and Deformation Mechanism of Equiaxed Fine-Grained Ti-45Al-7Nb Alloys

采用粉末冶金法制备了双相等轴细晶Ti-45Al-7Nb(原子分数)合金,研究了该合金在温度为900、950和1000℃以及应变速率为1×10^(−3)、1×10^(−4)和5×10^(−5) s^(−1)条件下的高温力学性能,并讨论了相应的变形机理。结果表明,在高温或低应变率下,Ti-45Al-7Nb合金的极限拉伸强度逐渐降低,但伸长率显著增加。由于细小晶粒容易实现变形和协调,其伸长率明显高于粗晶粒合金。高温拉伸后,合金在裂缝处形成大量的空洞,并在裂缝前部形成大量垂直于拉伸方向的长裂纹。此外,晶界的滑动、晶粒的孪生和动态再结晶也导致了合金变形,从而提高了微观组织的延展性。

The duplex Ti-45Al-7Nb(at%)alloys with equiaxed fine grains were prepared by powder metallurgy method.The high temperature mechanical properties of the alloys at 900,950,and 1000℃ under the strain rates of 1×10^(−3),1×10^(−4),and 5×10^(−5) s^(−1) were investigated,and the corresponding deformation mechanism was also discussed.Results show that the tensile strength is decreased whereas the elongation is greatly increased at elevated temperatures or under decrescent strain rates.Since the small grains are easy to achieve deformation and coordination,the elongation of the small grain alloys is significantly higher than that of coarse grain alloys.The alloys form a large number of voids at the fractures after high temperature tension.Long cracks perpendicular to the tensile direction are formed at the front fracture.Besides,the grain boundary sliding,grain twinning,and dynamic recrystallization also lead to the deformation of alloys,thus improving the microstructure ductility.