高温合金的高温疲劳裂纹扩展门槛值试验

Investigation on High Temperature Fatigue Crack Propagation Threshold Values of Superalloys

疲劳裂纹扩展门槛值反映材料抗裂纹扩展的能力,是重要的材料性能指标。室温疲劳试验已经成为标准试验方法,但是该方法能否拓展到高温下,并应用于高温合金,尚无试验数据。根据目前的测试技术,试验温度在600℃以下可以使用目测法进行裂纹扩展试验,而在600℃以上,由于试样表面氧化,目测无法观察,所以使用自动测量方法——直流电位法。但由于裂纹扩展门槛值试验时间很长(上百小时),试验难度非常大。该文介绍了粉末高温合金、变形高温合金以及定向凝固高温合金3种高温合金最高到850℃的疲劳裂纹扩展门槛值试验,使用目测法和直流电位法两种方法进行裂纹长度测量。结果表明:直流电位法可以用于高温疲劳裂纹扩展门槛值试验,但试验数据还存在一定的分散性,尚需进一步研究提高裂纹长度测量精度。

Fatigue crack propagation threshold value reflects material resistance to crack propagation and is an important material performance reference. Room temperature fatigue test has become a standard test method, but if the method can be extended to high temperature test and applied to superalloys, there has been no experimental data. Under the current testing techniques, when the temperature is below 600℃, the cracks can be measured by visual method. However, when the temperature is higher than 600 ℃, due to surface oxidation of the sample, the cracks can not be observed visually, and DC potential method as a automatic measurement method can be used. But the crack propagation threshold values test time is very long （hundreds of hours）, and the test is extremely difficul}c. The high temperature fatigue crack propagation threshold values test up to 850 ℃ of three kinds of superalloys including powder superalloy, wrought superalloy and directionally solidified superalloy were introduced, and the cracks length was measured by visual method and DC potential method. The results show that the DC potential method could be used in high temperature fatigue crack growth threshold values test, but there was still some dispersion of the test data, and further study was needed to improve the measurement accuracy of cracks length.