Artificial Defects in 316L Stainless Steel Produced by Laser Powder Bed Fusion: Printability, Microstructure, and Effects on the Very‐High‐Cycle Fatigue Behavior

Abstract

The printability of artificial defects inside the additively manufactured laser powder bed fusion (LPBF) 316L stainless steel is investigated. The printing parameters of the LPBF process are optimized to produce artificial defects with reproducible sizes at desired positions while minimizing redundant porosity. The smallest obtained artificial defect is 90 μm in diameter. The accuracy of the geometry of the printed defect depends on both the height and the diameter in the input model. The effect of artificial defects on the very‐high‐cycle fatigue (VHCF) behavior of LPBF 316L stainless steel is also studied. The specimens printed with artificial defects in the center are tested under VHCF using an ultrasonic machine. Crack initiation is accompanied by the formation of a fine granular area (FGA), typical of VHCF. Despite the presence of relatively large artificial defects, FGA formation is observed around accidental natural printing defects closer to the surface, which can still be considered as internal. The causes for this occurrence are discussed.

Fatigue Behavior of Additively Manufactured Stainless Steel 316L

“…Recently, investigation on the role of artificial defects was extended to VHCF [39], reporting in this case that the embedded artificial defects did not affect the VHCF behavior and crack initiation started from natural defects closer to the surface. In [60], the applicability of the √ area-parameter model was evaluated, showing a clear trend that suggests that the model can describe the fatigue strength for defects with √ area ≥ 1000 µm in L-PBF processed 316L steel.…”

“…Considering AM316L, most literature works adopted a Stress-based approach and the life range between 10 6 and 10 8 cycles is the most investigated. A few recent investigations considered the extension to Very High Cycle Fatigue (VHCF), but the literature is even scarcer [38,39]. Consequently, if not otherwise stated, fatigue results discussed in this review mainly refer to HCF.…”

Scaling of damage mechanism for additively manufactured alloys at very high cycle fatigue

“…Moreover, this steel has become a popular choice for additive manufacturing processes due to its excellent weldability and general versatility 3 . However, despite the extensive research on the fatigue characteristics of AM 316L stainless steel, there is a dearth of experimental information that is required to comprehend VHCF behavior 8 , 9 . The industrial use of AM 316L would be expanded with the help of such knowledge.…”