Influence of dwell time on fatigue crack growth in nickel-base superalloys

Engineered systems for high temperature service are often subjected to cyclic loads with dwell times at maximum load that can exacerbate fatigue damage evolution through creep and environment enhanced crack growth. Experiments are carried out to examine the influence of dwell time on fatigue crack growth in powder metallurgy (P/M) nickel-base superalloys in highpurity argon and oxygen at 873-973 K. This study complements a previous study on an ingot metallurgy (I/M) alloy. The data are analyzed using a general superposition model to capture the microstructural response to the conjoint actions of stress and environment. The model is validated through backward comparisons of the estimated time-dependent contributions with crack growth rate data from sustained-load tests. The mechanical and mechanistic implications of dwell time, the feasibility for inferring sustained-load crack growth rates from the dwell time tests, and the usefulness of the superposition model for life-cycle design and management of engineered structures are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.