Metallographic Studies on Duplex Stainless Steel Scaffold Fabricated by Laser Powder Bed Fusion

Duplex stainless steels (DSSs) consist of two-phase microstructure, ferrite (α) and austenite (γ) phases, which attracted attentions owing to its excellent combination of mechanical properties, corrosion resistance and biocompatibility. DDSs are known to be metallic materials suitable on a variety of technologically meaningful applications, as structures under corrosive environment, such as chemical engineering and biomedical engineering.

As per biomedical and bioengineering applications, topological designed metals show key role on repairing and replacing damaged bones. In this field, scaffold metals can significantly provide open spaces for the in-growth of bone tissue. Considering advanced production technology, additive manufacturing (AM) has significantly demonstrated the advantages of fabricating metal devices and metal parts with complicated or customized geometry. With a fine setup of processing parameters, Lase Powder bed fusion (L-PBF) technique is used to manufacture the DSS base components.

The aim of the present work is to perform the metallurgical analysis on cubic bulk DSS and topological designed Scaffold DSS fabricated by L-PBF, by investigating the evolution of mechanical and microstructural properties between cubic bulk and Scaffold DSS. Following such an approach, the samples were first cut in the YZ plane parallel to the printing growth direction and then inspected by optical and scanning electron microscopy (OM and SEM) for porosity quantification in terms of pores and void possibly formed during printing. The Scaffold DSS was also heat treated by annealing at temperature 1050° at two different durations: 30 min and 60 min, followed by water quenching. Microhardness test and nano-indentation were used for a complete mechanical characterization and to fully understand the evolution of the mechanical performance among the bulk, Scaffold DSS and the heat treated samples. Scaffolds were also inspected by XRD so to understand the effect of geometrical pores as well the effect the heat treatment on the evolution of the different phases. The experimental results report on the role of geometrical pores and heat treatments on the microstructure and mechanical properties of the tested materials.