Analysis of microporosity-dependent fatigue crack behavior in alloy 718 by using synchronic radiation X-ray CT and FEM

Abstract

Influence of microporosity on the mechanical properties of superalloy have been studied by numerical and experimental methods for long time. In this paper, the real morphology of microporosity in polycrystalline Alloy 718 specimens was inspected by synchronization radiation X-ray micron computerized tomography (µCT) and 3D model was reconstructed for the numerical simulation based on finite element method (FEM). Fatigue testing of the heat treated samples and heat isostatic pressured samples were conducted to verify the numerical analysis. Response surface analysis based on FEM was used to establish the linear function relationship between fatigue life and factors including of porosity, pre-deformation and residual stress. The simulation results showed that the interdendritic region on the surface of microporosity was the place of stress concentration in metal and the crack site of fatigue failure. Experimentally, heat treated sample fractured at microporosity, while the HIPed samples disrupted due to the matrix ductile fracture. The good agreement was obtained between the simulation and experimental results.