Assessment of specific contribution of residual stress generated near surface anomalies in the high temperature fatigue life of a René 65 superalloy

Abstract

This study evaluates the influence of residual stresses induced by the fabrication of surface anomalies on the fatigue crack growth in a nickel based superalloy. To separate the notch effect of the geometry from the residual stress field induced by fabrication of the surface flaws, two V‐type anomalies are considered: scratches and dents with equivalent morphology and size. A specially designed heat treatment has been used to reduce the magnitude of residual stresses around these anomalies in order to highlight their effects on the different stages of the crack propagation, under low cycle fatigue conditions at 400 °C. The crack initiation life is short for both anomalies but in the presence of compressive residual stresses, a decrease of the fatigue crack growth rate has been observed during the first stages of the crack propagation. Furthermore, the results showed that without residual stresses, scratches and dents exhibit the same behaviour. Thus, the residual stress field below surface anomalies is the main parameter controlling the fatigue life from surface anomalies.

Characterisation of handling and service surface damage on Nickel alloys caused by low velocity impacts of blunt hard objects

“…The effects of handling and service damage on the fatigue life of components is frequently estimated by empirical methods or ignored altogether. The work of Gourdin et al (2014Gourdin et al ( , 2016 on crack propagation near surface anomalies is one of the few references to handling damage in the literature. Currently, a crack propagation analysis of components with small scratches and dents is frequently made by assuming the damage geometry to be an initial crack of same length and depth.…”

“…Using the potential drop technique, Gourdin et al (2016) quantified the difference in crack initiation and propagation time between scratches and dents of similar geometry. Experiments were undertaken in the presence and absence of residual stresses; the latter achieved by a thermal treatment of the specimens in order to relax the residual stresses.…”

On the use of the √area△ and the three-parameter power function to estimate fatigue life of TC17 titanium alloy

“…The evidences indicate the scratch has an important role to initiate fatigue crack on blade root chamfer. Gourdin 5 found that the fatigue crack growth of natural cracks initiating from scratches without residual stresses is identical and similar to the long crack growth behavior of a nickel based superalloy. Inchekel and Talia 6 revealed that the fatigue life decreased sharply as the scratch depth increased and an edge scratch is more detrimental than a center scratch.…”

The effect of surface damage and residual stresses on the fatigue life of nickel superalloys at high temperature

“…It has also been shown that crack initiation in samples with surface damage is influenced by the same three factors suggested in [5]. In the work of Gourdin et al [9,10], the effect of scratches and dents on crack initiation and propagation was assessed by using a potential drop technique.…”