Mechanical characterisation of stainless steel parts produced by direct metal laser sintering with virgin and reused powder

Among the additive manufacturing (AM) techniques for metals available today, laser powder bed fusion (L-PBF) is the one that guarantees the highest dimensional accuracy and precision, compared with laser metal deposition (LMD) methods which, however, offer higher productivity and the possibility of repair applications. A drawback of all PBF processes is that all the build volume has to be filled up to the height of the tallest object to be produced (also in the case of a single object), even if not all the powder gets melted to obtain the desired parts and thus it may be reclaimed for reuse. However, excess powder participates in the process so that its chemical-physical characteristics will inevitably evolve through reuse cycles. Therefore, it is necessary to verify whether reusing it for subsequent AM runs is expected to cause a decay of the mechanical properties of produced parts. In this work, the effect of powder reuse is investigated for two kinds of precipitation hardening stainless steel, characterised by different primary microstructures: martensitic (EOS Stainless Steel PH1) and austenitic (EOS Stainless Steel GH1). Together with the variation of powder characteristics, both static and fatigue behaviour of parts produced with virgin and reused powder were compared by means of statistical techniques for data analysis. No significant variation, in terms of mechanical properties ascribable to powder reuse, was observed for EOS PH1, whereas EOS GP1 exhibited a sudden variation of both microstructure, from austenitic to martensitic, and mechanical properties after eight powder reuse times.