Effect of High Porosity on Bending Fatigue Properties of 3D Printed AISI 316L Steel

Abstract

Selective laser melting (SLM) is an effective way to produce optimized metallic parts in relatively short through-put times for various applications. The microstructure of SLM-manufactured metals is affected by the melting parameters applied, namely the total heat-input during SLM. The SLM processing can also introduce defects, such as pores and residual stresses in the part, resulting in impaired mechanical performance. Especially under dynamic loading, pores and microstructural defects can lead to premature cracking. In this study, the effects of melting parameters and the surface quality on the bending fatigue strength of SLM-manufactured AISI 316L austenitic stainless steel are demonstrated. Two sets of specimens were manufactured using two combinations of laser power and scan speed simulating a low and a high heat input. The specimens were heat-treated in a furnace at 600 °C for 120 min prior testing to relief the residual stresses. The surfaces were either as-built or electropolished conditions. The porosity existing in the specimens was estimated from the surface views. It was found that although the higher strength of the low energy density specimens increased the fatigue limit, the surface finish did not have any effect on it due to a high amount of porosity at sub-surface layers masking the effect of surface polishing.