Influence of microstructural defects and the surface topography on the fatigue behavior of “additively‐subtractively” manufactured specimens made of AISI 316L

Abstract

As additive manufacturing offers only low surface quality, a subsequent machining of functional and highly loaded areas is required. Thus, a sound knowledge of the interrelation between the additive and subtractive manufacturing process as well as the resulting mechanical properties is indispensable. In this work, specimens were manufactured by using laser‐based powder bed fusion (L‐PBF) with substantially different sets of process parameters as well as subsequent grinding (G) or milling (M). Despite the substantially different surface topographies, the fatigue tests revealed only a slight influence of the subtractive manufacturing on the fatigue behavior, whereas the different laser‐based powder bed fusion process parameters led to pronounced changes in fatigue strength. In contrast, a significant influence of subtractive finishing on the fatigue properties of the defect‐free continuously cast (CC) reference specimens was observed. This can be explained by a dominating influence of process‐induced defects in laser‐based powder bed fusion material, which overruled the influence of surface machining. However, although both laser‐based powder bed fusion parameter sets resulted in substantial defects, one set yielded similar fatigue strength compared to continuously cast specimens.

Post-processing of additively manufactured metallic alloys – A review

“…In view of manufacturing methods, AMprocessing (e.g., PBF-LB) to a large extent pre-determines the achievable surface integrity, whereas post-processing primarily determines dimensional and geometrical form (e.g., roundness, flatness) accuracy, as well surface topography (surface form and texture). For example, Blinn et al showed that the AM process overrules the influence of postprocessing (milling and grinding) on fatigue life due to pronounced effects of AM-induced defects [235]. Functional performance hence obviously depends on material as well, i.e., 1) its constitutive properties and 2) material-processing properties (AM-induced surface integrity, e. g., internal porosity, bond failures, residual stresses and cracks).…”

“…Removal of the surface and sub-surface defects using an appropriate machining process (within finishing range) was necessary to obtain reasonable fatigue performance for high-end applications where the parts are subjected to high alternating loads. Blinn et al [235] compared the HCF performance of PBF-LB/316L in as-built condition and after machining (milling and grinding) with that of continuously cast material subjected to similar finishing processes. In addition, two different printing strategies were examined to reveal the role of surface and sub-surface defects on the HCF before and after finishing processes.…”

Pós-processamento de peças metálicas produzidas por manufatura aditiva

“…Em termos de retificação, Yazdanpanah et al (2021) relataram uma melhora da rugosidade de 14,75 µm (SLMed) para 0,25 µm R a . Usando retificação pendular, Blinn et al (2021) reduziram a rugosidade inicial (após L-PBF) de 10,99±1,27 µm S a para 1,98±0,95 µm S a e 128,65±15,47 µm S z para 17,14±4,15 µm S z em cerca de 3,6 s. Usando retificação pendular e profunda, a rugosidade inicial (após laser-SLM) foi reduzida de 42-44 µm para 6,0 µm e 2,5µm R z , respectivamente (KIRSCH et al, 2020). Durante a fase de revisão sistemática da literatura, apenas três artigos supracitados avaliaram o impacto da retificação nas características superficiais de amostras de aço 316L fabricadas por MA.…”