Abstract
The present paper is focused on an experimental study of the damage-to-failure mechanism of additively manufactured 316L stainless steel specimens subjected to very high cycle fatigue (VHCF) loading. Ultrasonic axial tension-compression tests were carried out on specimens for up to 109 cycles, and fracture surface analysis was performed. A fine granular area (FGA) surrounding internal defects was observed and formed a “fish-eye” fracture type. Nonmetallic inclusions and the lack of fusion within the fracture surfaces that were observed with SEM were assumed to be sources of damage initiation and growth of the FGAs. The characteristic diameter of the FGAs was ≈500 μm on the fracture surface and were induced by nonmetallic inclusions; this characteristic diameter was the same as that for the fracture surface induced by a lack of fusion. Fracture surfaces corresponding to the high cycle fatigue (HCF) regime were discussed as well to emphasize damage features related to the VHCF regime.
Highlights
Recent studies have improved the quality of additively manufactured (AM) products [1,2,3,4,5].Despite marked progress, there is a lack of experimental data revealing the mechanisms of damage and failure of structures in real-life complex loading conditions, which represents a critical obstacle for the implementation of additive technologies in the serial production of critical parts [6]
The present study investigated the very high cycle fatigue (VHCF) damage-to-failure mechanism in 316L stainless steel specimens manufactured by laser powder bed fusion (L-PBF)
The obtained S–N diagram covering the high cycle fatigue (HCF) and VHCF regimes demonstrated the difference between the fatigue behaviors of the AM
Summary
Recent studies have improved the quality of additively manufactured (AM) products [1,2,3,4,5]. The properties of the final part highly depend on certain process parameters, such as the laser velocity and power density, scanning strategy, hatch spacing, and thickness of the printed layers [10,11] The combination of these parameters can be used to fabricate structures with typical defects present in AM metallic parts, such as a lack of fusion, voids, and microcracks induced by residual stresses [12]. Microcracks caused by the release of a high-stress field induced by a temperature gradient during laser melting leads to void formation [20] To diminish those microcracks, hot isostatic pressing (HIP) is applied. In the VHCF regime, crack initiation occurs in the core of the material and is accompanied by the growth of so-called fine granular areas (FGAs) in the vicinity of defects [22]. Conventional fatigue tests were performed to emphasize features of material damage in the VHCF regime
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