Fatigue Crack Propagation Behavior of IN738LC at Elevated Temperature

Abstract

Fatigue crack propagation behavior of IN738LC was investigated under two kinds of loading conditions. Load controlled (LC) tension-compression tests were carried out using center-cracked-tension specimens under the constant temperature condition. Obtained data was correlated with Paris law with the same exponent value and the effect of test temperature and frequency on the coefficient value was investigated. The coefficient value showed obvious dependency upon the loading frequency under the test temperature of 850℃ or higher. Thermal-mechanical fatigue (TMF) tests with out-of-phase cycling were also performed using cylindrical specimens, where temperature range was held constant at 400℃ and minimum temperature was either 400℃ or 500℃. In each test, fatigue loading was interrupted several times, and crack length was measured by means of replica technique. Obtained data was correlated with Paris law and compared with the data of LC tests. Crack propagation data of TMF tests tended to approach the data line of LC tests at the lower temperature, as the crack length became longer.