Investigation on High Temperature Fatigue Crack Propagation Threshold Values of Superalloys

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 difficult.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.