定向凝固UGTC47合金低周压缩保载疲劳过程显微组织演化

Microstructure Evolution of Directionally Solidified UGTC47 Alloy Under Low Cycle Fatigue with Compression Dwelling Time

摘要:

重型燃机涡轮叶片在高温下运行时，受离心力与热应力等应力的交替作用，易产生疲劳失效，从而对重型燃机的安全运行构成严重威胁。为使重型燃机平稳运行，通过应变控制的低周压缩保载疲劳试验，系统地研究了定向凝固UGTC47合金在疲劳循环过程中显微组织演化及其对疲劳性能的影响。研究发现，标准热处理态UGTC47合金在900和950 ℃下表现出不同的循环应力响应行为。UGTC47合金在900 ℃时存在显著的循环硬化、循环稳定和循环软化阶段，而在950 ℃时存在非常短的循环硬化，随即进入缓慢的循环软化阶段，直至快速软化失效。UGTC47合金在900 和950 ℃温度下，其应力应变迟滞回线均呈现显著的拉压不对称现象。标准热处理态UGTC47合金，在900和950 ℃低周压缩保载疲劳过程中出现不同程度的显微组织退化。UGTC47合金在900 ℃时，其枝晶干γ′相尺寸略有增加、立方度稍减小、体积分数无明显变化，也未形成γ′相筏排组织，且γ通道宽度增加较少，组织稳定性较好；在950 ℃时，合金枝晶干γ′相的体积分数在500周次出现显著降低，γ′相在100周次即形成P型筏排组织，且随着循环周次的增加，γ′相筏排完善程度和γ通道宽度迅速增加，显微组织退化速度明显大于900 ℃的。该研究结果为UGTC47合金在重型燃气轮机透平叶片上的应用提供了数据支撑，对于具有自主知识产权的燃气轮机叶片设计、使用具有不可或缺的工程价值。(专精特新·特殊环境材料服役行为专辑十五之十一)

Abstract:

When a heavy-duty gas turbine operates at high temperature， hot end components such as turbine blades are exposed to a series of cycle loading conditions， which may lead to fracture failure. In this study， low-cycle fatigue test with compression dwelling time under strain control was conducted and the microstructure evolution of UGTC47 alloy during fatigue and its influence on fatigue properties were systematically investigated. It is found that UGTC47 alloy with standard heat treatment shows different cyclic stress responses at 900 ℃ and 950 ℃. At 900 ℃ there is a significant cycle hardening， cycle stabilization stage and cycle softening stage， while at 950 ℃ it enters a slow cycle softening stage after a very short cycle hardening until rapid softening failure. The stress-strain hysteresis loops at both temperatures show significant tension and compression asymmetry. Microstructure degradation of the standard heat treated UGTC47 alloy during the low cycle fatigue at 900 ℃ and 950 ℃ is quite different. The microstructure showed good stability at 900 ℃. The volume fraction of γ' phase did not change significantly， the γ' phase size only increased slightly， the γ' phase basically remained square shape， no rafting structure was formed， and the γ channel width increased less. However， the situation at 950 ℃ was quite different. The volume fraction of γ' phase decreased significantly at 500 cycles， and P-type rafting of γ' phase was formed at the beginning of cycling about 100 cycles. With the increase of cycling， the rafting degree of the γ' phase and the width of γ channel increased rapidly. Microstructure degradation at 950 ℃ was significantly greater than that at 900 ℃. The results provide data to support for the application of UGTC47 alloy in heavy-duty gas turbine blades， and have significant engineering value for the design and use of gas turbine blades with independent intellectual property rights.