晶粒尺寸对GH720Li镍基合金蠕变-疲劳寿命的影响

The Effect of Grain Size on the Creep-Fatigue Life of GH720Li Superalloy

摘要:

为探明晶粒尺寸对涡轮盘材料——GH720Li镍基高温合金的蠕变-疲劳寿命的影响机理，本文开展了650℃下不同晶粒尺寸的GH720Li高温合金圆棒蠕变-疲劳试验研究。结果表明，晶粒尺寸对GH720Li高温合金的蠕变-疲劳寿命随着晶粒尺寸的减小而增加降低。而后，通过断口的SEM分析研究晶粒尺寸对GH720Li高温合金的蠕变-疲劳损伤影响机制。其失效机制主要为晶界的氧化起裂，而晶界长度随晶粒尺寸变小而增加。最后，本文对基于迟滞能量的损伤方程和机械功密度两种方法进行了修正，GH720Li合金的蠕变-疲劳寿命预测与试验结果吻合较好，验证了方法的准确性。

Abstract:

Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li, one of the most important turbine disk materials, at an elevated temperature of 650°C with different grain sizes, to investigate the mechanism of grain size on the creep-fatigue life of GH720Li. Experimental results shows that the creep-fatigue life of GH720Li superalloy will decrease with the decrease of grain size. SEM fracture analysis indicates that the oxidation and cracking is the main mechanism of GH720Li in the process of creep-fatigue under high temperature, and the smaller of grain size will result in the longer length of grain boundary. Finally, two methods including the damage function based on hysteresis energy and the applied mechanical work density (AMWD) are modified to predict the creep-fatigue life of GH720Li, which match well with experimental data.