Experimental investigation of creep crack growth behavior in nickel base superally by constant displacement loading method at elevated temperature

Creep crack growth (CCG) experiments were performed with compact tension (CT) specimens of a nickel base superalloy, FGH97, to investigate CCG rates and fracture behavior in the service temperature range from 600 °C to 750 °C. The constant displacement loading method (CDLM) was proposed and adopted since the constant force loading method (CFLM) are costly and time-consuming. Stress intensity factor (K) was employed to correlate the CCG rates (da/dt) for this creep-brittle superalloy and the general form of the K solution for a constant displacement loaded CT specimen was obtained based on finite element simulation. The test results indicate that the CCG rates increase with increasing temperature at a given K value. A unified formula containing temperature parameter was proposed to describe the CCG rates in the second stage of crack growth within this temperature range. A validating test in FGH97 via the CFLM was also carried out at 650 °C. Agreements in the test results indicate the feasibility of the CDLM.