An orientation-dependent creep life evaluation method for nickel-based single crystal superalloys

Abstract

This paper aims to propose a creep life evaluation method considering the effect of crystallographic orientation. First, the maximum Schmid factor of {111} 〈112〉 and the corresponding lattice rotation angle were introduced to form an “orientation factor”. Then the equivalent stress was calculated by multiplying this factor and the nominal stress. Latterly, the Larson-Miller Parameter (LMP) method was adopted as the rupture life evaluation criteria, in which the input variable was the equivalent stress instead of the nominal stress. All the predictions showed high accuracy when the proposed method was applied to Mar-M247, SC7-14, CMSX-2, Alloy454, CMSX-4 and DD6. Finally, the applicable temperature ranges of the orientation-dependent method (using equivalent stress) and the traditional LMP method (using nominal stress) were discussed. The results show that only the Orientation-Dependent (OD) method is reliable at intermediate temperatures (760–850 °C) because the orientation has significant effect on the stress rupture life, while the influence of orientation is considerably reduced at high temperatures. Both methods provide precise predictions in this situation, and the LMP method should be favored since it is much easier to implement.