Identification and characterization of spatter particles and their effect on surface roughness, density and mechanical response of 17-4 PH stainless steel laser powder-bed fusion parts

As an emerging additive manufacturing (AM) process, laser powder-bed fusion (LPBF) provides a new prospect for production of complex metallic parts. Laser-material interaction and melt pool dynamics govern the physics behind the LPBF process. However, instabilities in melt pool dynamics lead to the formation and ejection of spatter particles, which are known to change the powder-bed characteristics thus affecting the quality of printed parts. In this work, a comparative study is performed on the virgin and spatter powder particles where two types of spatter particles so-called: under-size (US) and over-size (OS) spatters are studied. Chemical composition, crystallographic phases, microstructure and morphology of the virgin powder as well as the US and OS spatters of 17-4 martensitic/precipitation hardened (PH) stainless steel (SS) powders are studied in detail. Particle analysis results show a significant morphology and size difference between the virgin (D90 – 60 μm) powder, US (D90 – 80 μm) and OS (D90 – 130 μm) spatters. Effect of spatter particles on the surface roughness, density and tensile response of printed parts is also studied. Compared to the parts printed in the non-spatter rich (NSR) region, parts printed in the spatter rich (SR) zone show a 15% and 28% increase in surface roughness for tensile and cylindrical samples, respectively. In addition, higher porosity is observed in these parts with larger pores. Moreover, tensile response shows an abrupt failure resulting in a reduction in ductility due to the presence of large pores (∼100 μm) observed on the fracture surface and x-ray computed tomography results.