In additive manufacturing by laser-powder-bed-fusion defect free printing is not always possible or feasible due to geometry dependent defects and stochastic defects, such as, gas entrapment pores. Some of the defects that have an impact on the mechanical properties are keyhole (KH) porosity due to high energy density, lack-of-fusion (LoF) porosity due to low energy density. In this study KH and LoF porosities were reproduced by adjusting processing parameters to understand the influence of these defects in the mechanical properties. Additionally, two printing parameters with optimal volumetric energy density (VED) and the machine vendors performance parameter were selected.
The porosity of the parts was confirmed using multiple 2D and 3D methods. The parts were tested in as-built condition and after a heat-treatment of 850°C for 2h in argon atmosphere, quenched in water aiming for good ductility and fatigue properties.
The static tests showed very similar yield strength (YS) and ultimate tensile strength (UTS) within the two printing parameters with optimal VED in the as built and heat-treated state, respectively. The samples in the heat-treated state experienced a decrease in YS and UTS accompanied by an increase in expected ductility. The samples with either KH or LoF porosity showed a decrease in YS and UTS compared to the parts with optimal VED and same heat-treatment.
The fatigue behavior of the heat-treated parts was measured using rotational bending. The parts were tested with the as built roughness and after machining.
Considering only parts without machining, all parameters show similar fatigue performance, indicating that roughness dominates over the effects caused by the porosity. In the samples with the machined surface the different VED in the printing parameters does have a significant influence on fatigue.
In this work, it was shown that with proper heat treatment and surface condition, productivity parameters can have mechanical properties very similar as high performance parameters and that KH or LoF defects have different impact in the mechanical properties.