Artificial porosity introduced during L-PBF of IN718,and its effect on fatigue performance before and after HIP

Abstract

During laser powder bed fusion (L-PBF), the protective atmosphere, normally argon, can become trapped in cavities formed during the process. We have demonstrated this by introducing ø0.5 mm pores in the CAD file (totalling 0.5% by volume) and measuring a threefold increase in argon content, versus an identical IN718 build-job without pores. For critical applications where the material is subjected to cyclic loading, any defects can act as stress raisers and initiate cracks. The pores that were introduced drastically reduced the fatigue performance of said material. However, after Hot Isostatic Pressing (HIP), the material regained its properties as if the pores were never introduced. Still, the argon remains after HIP according to measurements as it lacks solubility and thus cannot leave the material. Worth noting is that a small quantity of argon originates from gas-atomisation of the powder and thus does not leave entirely during the remelting in L-PBF.