论文部分内容阅读
为了研究在高温下常见的疲劳裂纹扩展速率在低频下显著增加的现象而进行了本研究工作。对两种不同热处理状态的lnconel718合金,在空气和氦_7环境中于650℃进行了蠕变试验和0.01、0.1与1.0Hz三种频率下的疲劳试验。蠕变裂纹扩展速率在空气中比在氦中快50～100倍。在氦中的疲劳试验表明,裂纹扩展速率对频率几乎不敏感;但在空气中的试验表明,在较低频率下,裂纹扩展速率显著增加。这些结果说明,无论在蠕变试验还是在疲劳试验中,空气环境都起了主要的作用。氧扩散到晶界中好象是加速空气中裂纹扩展的原因。过时效热处理降低了裂纹扩展速率。
In order to study the phenomenon that the fatigue crack growth rate, which is common at high temperature, increases significantly at low frequency, this work was carried out. Two different heat treatment conditions lnconel718 alloy, air and helium _7 environment at 650 ℃ creep test and 0.01,0.1 and 1.0Hz fatigue test at three frequencies. Creep crack propagation rates are 50 to 100 times faster in air than in helium. Fatigue tests in helium show that crack growth rate is almost insensitive to frequency; however, experiments in air show that crack growth rates increase significantly at lower frequencies. These results show that the air environment plays a major role, both in creep tests and in fatigue tests. The diffusion of oxygen into the grain boundaries seems to be the reason for accelerating the crack propagation in the air. Overaging heat treatment reduces crack propagation rate.