DD9合金在蠕变过程中的组织演变

Microstructure Evolution During Creep of Single Crystal Superalloy DD9

摘要:

对单晶高温合金DD9在980 ℃/250 MPa和1100 ℃/137MPa条件下进行了蠕变中断与断裂试验。通过扫描电镜、透射电镜分析了蠕变过程中的微观组织演变。结果表明：在980 ℃/250 MPa和1100 ℃/137MPa蠕变条件下，合金的微观组织演变过程类似。弥散分布于γ基体中的立方状γ′相逐渐演化成垂直于应力方向的层状结构。γ基体通道平行于应力方向的宽度在蠕变过程中逐渐增加。γ基体通道宽度的增加与应变之间的关系在对数形式下满足线性关系，即γ基体宽度可以通过应变来推断，这可能为研究单晶高温合金在高温低应力蠕变过程中γ基体的宽度变化提供了一种方法。在蠕变早期，γ相中形成的位错首先通过交滑移在γ/γ ′界面形成相互垂直的位错网，随后在高温下，外部应力和错配应力的耦合作用使得位错网演变为稳定的六边形态。在蠕变后期，位错剪切γ ′相，直至试样断裂。

Abstract:

Interrupted and ruptured creep tests were conducted on single crystal superalloy DD9 at 980 °C/250 MPa and 1100 °C/ 137 MPa conditions. Microstructure evolution during creep was analyzed through scanning electron microscope and transmission electron microscope. Results show that the microstructure evolutions are similar under the creep conditions of 980 °C/250 MPa and 1100 °C/137 MPa. Cubical γ′ phase, which is dispersedly distributed in the γ matrix, gradually evolves into a layered structure perpendicular to the stress direction. The width of the γ matrix channel along the direction parallel to the stress increases. The relationship between the increase in width of the γ matrix channel and the strain satisfies linear relationship in logarithmic form, indicating that the width of the γ matrix can be deduced via the strain under creep state. This may provide an approach to investigate the width of γ matrix in single crystal superalloys during creep under high temperature and low stress conditions. In the early creep stage, dislocations formed in the γ phase generate mutually perpendicular networks through cross-slip at the γ/γ′ interface. Then, stable hexagonal dislocation networks form as a result of the coupling effects of external stress and mismatch stress at high temperatures. In the later period of creep, dislocations shear the γ′ phase, ultimately causing the fracture.