GH720Li镍基高温合金蠕变-疲劳试验研究

对先进航空发动机涡轮盘的典型材料镍基高温合金GH720Li的蠕变-疲劳特性进行了试验研究。通过对真实涡轮盘上取样的圆棒试验件,开展了650℃不同保持时间下的GH720Li合金蠕变-疲劳试验。结果表明,650℃下保持时间对GH720Li合金的蠕变-疲劳特性影响较大,即,在较长的保持时间(30 min)下,蠕变损伤占主导地位,降低了材料的蠕变-疲劳寿命。SEM断口分析表明:随着保持时间的增加,裂纹形成区由穿晶和沿晶混合断裂向沿晶断裂转化;裂纹扩展区由穿晶断裂向穿晶、沿晶的混合模式转化。最后,基于GH720Li合金的蠕变-疲劳试验数据,分别选取载荷谱转换法和机械功密度法进行GH720Li合金的蠕变-疲劳寿命预测,并研究了2种模型的工程适用性。

Experimental study on creep-fatigue test of nickel-based superalloy GH720Li

In this paper, the creep-fatigue behavior of a nickel-based superalloy GH720Li widely used for the turbine disk of an aero-engine was experimentally investigated. The cylindrical bars cut from an actual turbine disk were employed. The creep-fatigue tests with different dwell times were performed at 650°C. Experimental results revealed GH720Li is very sensitive to dwell time at 650°C, i.e., at the longer hold time (> 30min), the creep damage is dominant, thus decreases the creep-fatigue life. Then, the mechanism of creep-fatigue failure was discussed by using the SEM analyses of the fracture surface. It was found that with the increase of dwell time, the failure mode of the crack formation zone is transformed from a mixture of transgranular and intergranular to an intergranular failure. In addition, the crack formation zone is transformed from an intergranular fracture to a mixture failure mode. Finally, based on the experimental data, loading patterns transformation method and AMWD method were applied to predict the creep-fatigue life, and the applicability of two models was discussed.