Effect Of Microstructure And Initiation Defect On Small Fatigue Crack Initiation And Propagation Of Ni-based Superalloy GH4169

As the the problem of small crack submitted by Pearson in 1975, and the development of aerospace engineering, people suggested more serious requirement for design method of key component of aerospace engine. Traditional fracture mechanic theory can't meet the high accuracy of damage tolerance design method, and the similarity concept of fracture mechanic theory no longer suitable for small crack. However some research suggested that the stage of small crack initiation and propagation account for the large part of fatigue life. So the study of small crack initiation and propagation behaviors and their influence factors is reasonable and important. The material studied in this paper is GH4169 nickel alloy used in turbine discs. By changing the heat treatments and prefabricating different three dimension defects, and then studying their effects on small crack initiation and propagation. The major contents and conclusions are summarized as followed:(1) Conducting four kinds of heat treatments to change grain size and the morphology intergranular strength phase, and analyzing the variation regularity of microstructure influenced by heat treatment.(2) At 650?, no matter which kind of microstructure, the crack length of GH4169 alloy where small crack transform to long crack are all corresponding to ten average grain size. The life ratio of small crack initiation and propagation stages decreases from 90% to 50%-60% with the increasing of average grain size.(3) At room temperature, the fatigue life of GH4169 alloy specimen major influenced by the variation of the defect length, increasing of the defect length will cause the decreasing of fatigue life of specimen. The fatigue life of specimen will increase significantly when the aspect ratio of defect near 1. And the depth of defect is deeper, the fatigue life of specimen is longer when the aspect ratio is similar.