Porosity control during directed energy deposition additive manufacturing through La2O3 particle additions

Porosity in laser powder-based directed energy deposition (DED) additive manufactured alloy components may compromise mechanical performance. This study demonstrates how La2O3 particles blended with gas atomised RR1000 Ni-based superalloy powder affect pore evolution, reducing the occurrence of porosity, especially large pores. Using correlative in situ high-speed synchrotron X-ray and infrared imaging coupled with multiphysics modelling, we reveal the underlying melt flow and pore evolution behaviour with and without La2O3 additions. A 0.2 wt.% La2O3 particulate addition produces a pore-lean build with notably fewer large pores. We propose this occurs through two mechanisms involving La2O3 on the surface altering thermo-fluid conditions within the melt pool: (1) a reduction of melt pool surface tension gradient and hence Marangoni flow, and (2) an increased melt pool absorptivity. Additionally, La2O3 enhances powder capture efficiency and promotes the formation of a predominantly equiaxed, fine-grained microstructure.