Crack growth in structural materials under the combined action of fatigue and creep (review)

We analyze the specific features of the behavior of metals under conditions of high-temperature creep-fatigue fracture. The main approaches to predicting the life of metal structures are considered. Furthermore, we describe the results of numerous investigations of the high-temperature creep-fatigue behavior of different alloys that are used for producing turbine elements, components of power plants, pipelines, etc. Some general properties of these processes are analyzed. For example, longer holding times and lower cycling frequencies often lead to an increase in the crack growth rate and in its intragranular propagation. As a rule, these effects are more appreciable at elevated temperatures and more pronounced in oxygen environments than in inert. The level of such effects, especially in environments with oxygen, depends substantially on the parameters of microstructure, in particular, grain sizes and shape as well as the chemical properties of their boundaries. Some of these factors are considered in more detail.