压应力下Ti-1300合金时效过程中相变与组织演化

Phase Transformation and Microstructure Evolution during Isothermal Aging of Ti-1300 alloys under Compress Stress

通过膨胀法、扫描电镜(SEM)和电子背散射衍射(EBSD)等方法和技术手段研究了压应力下Ti-1300合金在等温时效过程中βm→α+β相变动力学和组织演化规律。结果表明:压应力作用下Ti-1300合金在等温时效过程中βm→α+β相变动力学方程可用Johnson-Mehl-Avrami(JMA)方程表示,并拟合出来Avrami指数,用于表征相变机制;Ti-1300合金在40 MPa压应力的βm→α+β相变机制与无应力状态下的相似;当合金在600℃时效时的相变机制为开始是在位错线上进行形核,随后形核率迅速衰减为零,随着次生α相的析出,转而在α/β界面上形核,并且形核位置很迅速又饱和,形核率再次衰减为零;而当合金在700℃时效时的相变机制主要为界面形核。但Ti-1300合金在40 MPa压应力下进行等温时效时,组织演变表现出明显的α相择优取向效应。通过分析Ti-1300合金进行双级时效的显微组织发现, Ti-1300合金在等温时效过程中引入外加压应力后,外加压应力对合金中α相应力取向效应的影响主要在α相的形核阶段,对α相的长大阶段影响不明显。

The kinetics of isothermal phase transition β_m→α+β and microstructure evolution of Ti-1300 alloy under compressive stress were investigated using dilatometry, scanning electron microscope(SEM) and electron back-scatter diffraction(EBSD). The results showed that the Avrami indexes of phase transformation kinetics for Ti-1300 alloys could be simulated with Johnson-Mehl-Avrami(JMA) equation under compress dress, which were used to present solid transformation mechanism. The phase transformation mechanism of β_m→α+β in Ti-1300 alloys under compress stress of 40 MPa was similar to that of no stress. The mechanism of β_m→α+β of the alloy isothermal aged at 600 ℃ was to nucleate at dislocation in the first stages, then the nucleation rate rapidly attenuated to zero. With the precipitation of secondary α phase,α phases started to nucleate at the α/β interface, and the nucleation site was saturated so fast that the nucleation rate attenuated to zero again, while the β_m→α+β phase transition mechanism of the alloy aged at 700 ℃ was mainly interface nucleation. Moreover, it was found that compress stress of 40 MPa exerted positive imparts upon α platelets variation selection when Ti-1300 alloys were aged at isothermal conditions. Additionally, after investigating microstructure evolution of the alloy in the double stage aging process, it was found that compress stress played an essential role in nucleation stage of α phase in the Ti-1300 alloys in the isothermal stress aging process, and there was no obvious influence on α phase growth stage.