Residual stresses in AM components: Print orientation study with neutron diffraction

Prabhat Pant¹, Sebastian Proper², Vladimir Luzin³ , Sören Sjöström¹ , Kjell Simonsson¹ ,Johan Moverare¹ , Seyed Hosseini², Victor Pacheco⁴, Ru Peng¹

¹Linköping University, Dept. of Management and Engineering, Linköping, Sweden, ²RISE, Sweden, ³ANSTO, Australia, ⁴Uppsala University, Uppsala, Sweden

High level of residual stresses (RS) developed during the powder bed fusion method of additive manufacturing (AM) is one of the key hindrances to overcome for manufacturing  quality parts of complex geometries in terms of mechanical properties. Additive manufacturing has a wide variety of processing parameters that can influence the residual stress distribution and magnitude as well. The orientation of part while building is one of the main parameters that have an influence on the RS. Till now the building orientation has been chosen according to parts shape, size, and the number of components that must fit in the chamber for a high productivity rate. Lack of knowledge of building orientation influence on RS state can cause the parts to distort during the printing process and can cause cracks in the parts as well. Therefore, knowledge about the residual stress in different printing orientations can be helpful to decide the optimal way to print complex parts without compromising mechanical integrity. To gain more insight on this, three L- shaped samples were printed in different orientations namely: horizontal (HB), vertical (VB), and 45° angle (45B). These samples were made of Nickel-based superalloy Inconel718 and manufactured using the laser-based powder bed fusion method and the samples were removed from the base plate for experimental analysis. The RS distribution was resolved using the neutron diffraction technique. From the experiment, it was observed that in general RS changes from compression inside the part to tension near the surface of the part, and the HB part has shown the least amount of residual stress among the three samples tested.