Lifetime Prediction Under Constant Load Creep Conditions for a Cast Ni-Base Superalloy

Creep and stress-rupture properties of cast IN-738LC turbine blades have been analyzed to review the suitability of the Monkman-Grant relationship as a reliable life prediction method where tr es m = C and m and C are material constants. The constants m and C in the Monkman-Grant relationship are temperature dependent and the relationship predicts lives within a factor of ±4 relative to the observed values. A modified form of this relationship is derived where (−b tr n1 + tr ) es m1 = K and b, n, m1 , and K are material constants. The modified relationship is more accurate and predicts lives within a factor of 2 relative to the observed values. The constants b, n, m, and k are independent of stress and temperature.