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Abstract
In this paper, the influences of build orientation and post-fabrication processes, including stress-relief, machining, and shot-peening, on the fatigue behavior of stainless steel (SS) 316L manufactured using selective laser melting (SLM) are studied. It was found that horizontally-built (XY) and machined (M) test pieces, which had not been previously studied in the literature, in both stress-relieved (SR) or non-stress-relieved (NSR) conditions show superior fatigue behavior compared to vertically-built (ZX) and conventionally-manufactured SS 316L. The XY, M, and SR (XY-M-SR) test pieces displayed fatigue behavior similar to the XY-M-NSR test pieces, implying that SR does not have a considerable effect on the fatigue behavior of XY and M test pieces. ZX-M-SR test pieces, due to their considerably lower ductility, exhibited significantly larger scatter and a lower fatigue strength compared to ZX-M-NSR samples. Shot-peening (SP) displayed a positive effect on improving the fatigue behavior of the ZX-NSR test pieces due to a compressive stress of 58 MPa induced on the surface of the test pieces. Fractography of the tensile and fatigue test pieces revealed a deeper understanding of the relationships between the process parameters, microstructure, and mechanical properties for SS 316L produced by laser systems. For example, fish-eye fracture pattern or spherical stair features were not previously observed or explained for cyclically-loaded SLM-printed parts in the literature. This study provides comprehensive insight into the anisotropy of the static and fatigue properties of SLM-printed parts, as well as the pre- and post-fabrication parameters that can be employed to improve the fatigue behavior of steel alloys manufactured using laser systems.
Highlights
Additive manufacturing (AM) has been recognized over the last three decades as one of the revolutionary manufacturing technologies in various industrial areas, such as military, medical, devices, aerospace, and automobile industries
This paper describes the influences of build orientation and post-fabrication processes on the fatigue behavior of stainless steel (SS) 316L fabricated via the Selective laser melting (SLM) method
The influence of surface roughness on the fatigue resistance of test pieces produced with different surface and heat treatment conditions will be potentially manifested in the S-N diagram, as well as the fracture surfaces examined using scanning electron microscopy (SEM)
Summary
Additive manufacturing (AM) has been recognized over the last three decades as one of the revolutionary manufacturing technologies in various industrial areas, such as military, medical, devices, aerospace, and automobile industries. Materials 2019, 12, 4203 the main fabrication methods for manufacturing parts out of metals in stainless steel, nickel, titanium, and aluminium alloys [1,2,3,4,5,6]. The improper choice of metal AM process parameters, such as the powder material type, power density of the laser, velocity and method of scanning, and thickness of the layer, can result in the formation of defects of a different morphology, number, and size, which influence the mechanical behavior of the material. A lack of fusion (LOF) holes of irregular shapes, and cracks are the three well-known types of defects. Bauereiß et al [7] explained that spherical porosity has a random distribution within the parts, while LOF holes are spread between the layers
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