Low cycle fatigue is a major concern for rotary components like the compressor disk made in Ti17. The dispersion in fatigue life could be very important and the ex-β grains inherited from the β-forging process seems to be implicated. So the goal of this work is to: - understand and simulate the crystallographic evolution of the β phase during β-forging - study the impact of crystalline orientation of β grains (bcc) and α plates (hcp) on fatigue - analyse the effects of modifications on the loading path on the texture that partly influences the dispersion in fatigue life A polycrystalline model was used to simulate the β grains evolution during β-forging in an actual 3D aggregate (determined by EBSD). The texture obtained numerically is in good agreement with experiment. The formation of millimetric crystallographic zones composed of clusters of grains with or direction aligned with the forging direction, experimentally observed, is predicted by the model. In order to decrease the size of the crystallographic zones a modification of the loading path was simulated. A minimum of texture is clearly found. The experimental study points out the impact of the strain rate on the morphology and texture. The fatigue study has shown that a crystallographic family of α plates, related to the forged β grains orientation, tends to favour multiple crack nucleation. Simulations of the local behaviour of α/β microstructure, under macroscopic elastic loading, point out the first active slip systems at α/β interface correspond to the observed fatigue crack nucleation.
