粉末高温合金 FGH4095 的蠕变疲劳裂纹扩展行为研究

Creep-fatigue crack growth behavior of sintered metallurgy superalloy FGH4095

摘要

粉末高温合金具有优异的高温力学特性及热加工性能，广泛使用于先进航空发动机零部件。针对粉末高温合金 FGH4095 的盘形件，通过取样试验，利用原位观察方法测量了其在 20 ℃、530 ℃、630 ℃和 700 ℃及应力比 0.1、-1 下的裂纹扩展速率曲线及门槛值，运用 Paris 规律得到了稳态裂纹扩展特性参数，分析了各特性参数的温度依存性。研究发现蠕变对裂纹扩展行为有显著影响，高温下，应力比 0.1 的扩展曲线斜率更大，且不再具有门槛值。研究还发现 FGH4095 的裂纹扩展性能随温度增高并非单调变化，并结合手册数据对此现象进行了说明。基于损伤演化理论对蠕变疲劳耦合损伤下的裂纹扩展行为进行了分析，说明了裂纹扩展速率曲线的频率依存性及 Paris 规律应用的局限性。通过引入疲劳特征长度的概念，讨论了利用频率依存的裂纹扩展数据对各类裂尖（包括大裂纹和小短裂纹）问题进行蠕变疲劳寿命评价的方法。

Abstract

Sintered superalloys have been widely used in advanced aero engine parts due to their excellent high temperature mechanical properties and hot workability. Sampling tests are carried out for disc-shaped part of FGH4095. The crack growth rate curves and threshold values of FGH4095 are measured at 20 ℃，530 ℃，630 ℃，and 700 ℃ with stress ratios 0.1 and -1 by in-situ observation method. The steady-state crack growth parameters are obtained by Paris law，and the temperature dependence of each parameter is analyzed. It is found that creep has a significant effect on crack propagation behavior. At high temperature，the slope of crack growth rate curve with stress ratio 0.1 is greater than that with stress ratio -1，and threshold value with stress ratio 0.1 is no longer observable. It is also found that the crack growth performance of FGH4095 would not change monotonically with the increase of temperature，and this phenomenon is explained by the data manual. Based on the damage evolution theory，the crack growth behavior under creep-fatigue coupling damage is analyzed，the frequency dependence of crack growth rate curve and Paris law's limitation are illustrated. Based on fatigue characteristic length，this paper discusses a new method for evaluating creep-fatigue life of all kinds of crack tips （including large cracks and short cracks） using frequency-dependent crack propagation data.

关键词

粉末高温合金 / 蠕变疲劳 / 裂纹扩展速率 / 门槛值 / 特征长度

Key words

sintered superalloy / creep-fatigue / crack growth rate / threshold value / characteristic length

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基金资助

国家重大科技专项资助项目(J2019-IV-0008-0076)