近α型高温钛合金长期时效过程中的组织演化行为

Microstructure evolution behavior of near alpha type high temperature titanium alloy during long-term aging

利用光学显微镜、扫描电镜和透射电镜研究了Ti600高温钛合金在550℃长期时效至2000 h过程中的微观组织演化行为与机理。结果表明:Ti600合金在550℃长期时效下稀土相较为稳定,但α_(2)相和硅化物S_(2)相析出并逐渐长大。0~500 h的时效初期,随时效时间的增加,与基体共格的球状α_(2)相的尺寸和数量增加,但当时效至500 h后,α_(2)相的析出与长大趋于稳定,时效至2000 h,α_(2)相的尺寸仍保持在10 nm以内。硅化物S_(2)相在α片层与β相界面或α相内析出,且当时效时间超过200 h后其长大逐渐明显,并且沿着长轴方向生长使其形状逐渐向棒状转变。时效至2000 h,合金中S_(2)相的平均尺寸已经达到约175 nm。经计算,550℃长期时效S_(2)相的长大速率K=2.69×10^(3) nm^(3)·h^(-1)。其中Zr的扩散主要控制S_(2)相的长大。

Microstructure evolution behavior and mechanism of high temperature Ti600 titanium alloy during long-term aging at 550 ℃ for 0-2000 h were studied by means of optical microscope,scanning electron microscopy and transmission electron microscopy.The results show that the rare earth phase in the Ti600 alloy is maintained relatively stable during long-term aging at 550 ℃,but α_(2) phase and silicide S_(2) phase are promoted to precipitate and grow up.At the early stage of aging,the size and number of spherical α_(2) phase coherent with the matrix increase as the aging time increases from 0 to 500 h.However,after aging for 500 h,the precipitation and growth of the α_(2) phase tend to be stable.After aging for 2000 h,the size of the α_(2) phase remains within 10 nm.The silicide S_(2) phase is induced to precipitate at the interface between the lamella α and β phase or within the α phase,and its growth gradually becomes obviously after the aging time exceeds 200 h,and it grows along the long axis direction,gradually transforming its shape into a rod shape.After aging for 2000 h,the average size of the S_(2) phase in the alloy has reached about 175 nm.After calculation,the growth rate of the S_(2) phase during long-term aging at 550 ℃ is K=2.69×10^(3) nm^(3)·h^(-1).The diffusion of Zr mainly controls the growth of the S_(2) phase.