Additive manufacturing of fatigue resistant austenitic stainless steels by understanding process-structure–property relationships

Abstract

The limited understanding of additive manufacturing process-structure-property interrelationships raises some concerns regarding the structural reliability, which limits the adoption of this emerging technology. In this study, laser beam-powder bed fusion is leveraged to fabricate an austenitic stainless steel with a microstructure containing minimal known crack initiation features. Ex-situ microstructural observations of the crack initiation features and mechanisms are carried out for interrupted fatigue tests via electron backscatter diffraction mapping of the micro-cracks. Results show that the additive manufactured stainless steel alloy has improved fatigue resistance compared to its wrought counterpart as a result of the unique microstructural features. IMPACT STATEMENT Using an experimental ex-situ microstructural investigation, the fatigue resistance of additive manufactured 304L stainless steel was shown to be superior to the wrought counterpart by avoiding the typical failure mechanisms.

Enhancing ductility and fatigue strength of additively manufactured metallic materials by preheating the build platform

“…Preheating the build platform then can considerably assist with reducing the volumetric defects and potentially enhance the fatigue performance of AM materials. It is worth noting that the fatigue performance of 300 SS series is not much sensitive to defects and their effects are typically alleviated by the microstructure and ductility 23 . As can be seen in Figure 11A, for an NP specimen (NP_1 specimen) tested at 0.00175 mm mm −1 of strain amplitude, the crack initiated from a large LoF defect ( = 264 μm) close to the surface; however, the fatigue life is still considerably long due to the low sensitivity of this material to the defects.…”

“…It is worth noting that the fatigue performance of 300 SS series is not much sensitive to defects and their effects are typically alleviated by the microstructure and ductility. 23 As can be seen in Figure 11A, for an NP specimen (NP_1 specimen) tested at 0.00175 mm mm −1 of strain amplitude, the crack initiated from a large LoF defect ( ffiffiffiffiffiffiffiffiffi area p = 264 μm) close to the surface; however, the fatigue life is still considerably long due to the low sensitivity of this material to the defects. For the P150 LB-PBF 316L SS counterpart (P150_1 specimen) tested at the same strain amplitude level (i.e., 0.00175 mm.mm −1 ), the fatigue life is 2.5 times longer than the NP specimen.…”

“…The commonly used 316L SS is chosen for the experimental programme in this study because of its higher ductility and lower sensitivity to volumetric defects under cyclic loading. 23 Therefore, if there are any effects of build platform preheating on the fatigue strength of LB-PBF 316L SS, greater effects are expected for materials with less ductility and more sensitivity to volumetric defects.…”

“…Therefore, the goal of this study is to evaluate the effect of build platform preheating not only on the microstructure/defect structure but also on the mechanical properties, in particular, the fatigue resistance of LB‐PBF‐processed metallic materials. The commonly used 316L SS is chosen for the experimental programme in this study because of its higher ductility and lower sensitivity to volumetric defects under cyclic loading 23 . Therefore, if there are any effects of build platform preheating on the fatigue strength of LB‐PBF 316L SS, greater effects are expected for materials with less ductility and more sensitivity to volumetric defects.…”

Evaluation of the effects of the metal foams geometrical features on thermal and fluid-dynamical behavior in forced convection

“…AM represents an effective and viable alternative in the production of items characterized by complex geometries when the standard subtractive processes are too expensive. The samples realized with this kind of process are valuable for structural applications [33][34][35][36][37]. In particular, Calleja et al [38][39][40] worked on the improvement of laser cladding technology for the realization of structural customized parts with structural performances and reduced weight.…”