试验温度对镍基单晶高温合金裂纹扩展行为的影响

Effect of Test Temperature on Crack Propagation Behavior of Nickel-Based Single-Crystal Superalloy

摘要:

研究了DD6镍基单晶高温合金从530 ℃到850 ℃的疲劳裂纹稳定扩展行为。疲劳裂纹扩展试样沿[001]方向平行于受拉的加载轴。通过扫描电子显微镜研究疲劳裂纹扩展试验后的断口形貌，并根据形貌特点分为源区、预制裂纹区、稳定扩展区以及快速扩展区。通过电子背散射衍射技术研究垂直于断口的剖面塑性变形情况。通过透射电子显微镜观察断口附近位错机制随温度的变化。结果表明，受温度场、应力场以及暴露时间的作用，在650 ℃时发生氧化，且在650 ℃至760 ℃之间，由于γ′相的弱化，在γ与γ′相中形成大量连续的位错，导致合金氧化加剧，同时760 ℃下疲劳扩展寿命显著下降。

Abstract:

The fatigue crack propagation behavior of DD6 nickel-based single-crystal superalloy was investigated at temperatures ranging from 530 °C to 850 °C. The fatigue properties were assessed along the [001] direction, parallel to the loading axis in tension. After the fatigue crack propagation test, the fracture morphology was examined by scanning electron microscope and classified into four zones, including source zone, prefabricated crack zone, stable extension zone, and rapid extension zone. Electron backscatter diffraction was utilized to observe the profiles of plastic deformation perpendicular to the fracture. Additionally, the dislocation motion mechanism near the fracture was studied by transmission electron microscope. Results show that oxidation occurs at 650 °C under combined influences of the temperature field, stress field, and exposure time. Furthermore, due to weakened γ′ phase, a significant number of consecutive dislocations form in the γ and γ′ phases between 650 and 760 °C, resulting in increased oxidation of alloy. Besides, a notable decrease in fatigue propagation life can be observed at 760 °C.