Effect of Stress Ratio on Fatigue Crack Propagation Behavior of Single Crystal Superalloy

Abstract

In order to study the impact of different stress ratio on the fatigue crack growth behavior of DD6 single crystal superalloy, the fatigue crack growth rate test of different stress ratio (R = 0.05, 0.2, 0.5, 0.6) at 530 °C was conducted, the influence of stress ratio on crack growth rate was studied, and the growth of crack extension rate was corrected by normalization method. The results show that the section includes the fatigue fracture section perpendicular to the load and an angle to the load. The flat section is the main section representing the crack extension. The oblique section is formed with the change of the crack extension load state, and its occurrence is related to the dispersion of (da/dN)−Δk data, reflecting the uniqueness of single crystal. The Paris formula better characterized the crack expansion behavior of DD6 alloy, and the stress is more sensitive than the crack growth rate in the early stable growth phase. Crack growth rate normalized characterization equation constructed under different stress ratios are predicted to be within the 1.3-fold dispersion band.