Influence of phase coarsening on fatigue crack growth in precipitate strengthened alloys

Abstract

The precipitate size and distribution within precipitate strengthened alloys will change significantly after phase coarsening, and it will further affect their mechanical properties. In this paper, the fatigue properties of alloys during phase coarsening processes are investigated. The fatigue crack growth in various microstructures under the low cycle fatigue condition is analyzed systemically, and several aspects such as the cyclic deformation and failure morphologies, cyclic stress, and crack growth rate, are discussed in detail. Especially, a mechanism analysis is conducted, which is based on evolutions of internal variables within the material, e.g., stress state and plastic strain. The influence of phase coarsening on the crack propagation is also discussed. Related analysis demonstrates that the microstructure of alloys plays an important role in their fatigue properties. During the phase coarsening process, the fatigue strength of alloys descends gradually, the fatigue crack deflection becomes more serious, the propagation becomes more unstable, and the crack growth rate increases. Besides, related degradations derived from phase coarsening are more distinct under the higher external load. The corresponding fatigue properties are closely related to the plastic deformation as well as the dislocation movement within the alloys. The variation of the precipitate size and distribution alters the interaction manners between the precipitate particles and the plastic deformation bands or cracks within the microstructure, which further leads to different fatigue characteristics of alloys.