Increasing the Productivity of Laser Powder Bed Fusion for Stainless Steel 316L through Increased Layer Thickness

Abstract

Additive manufacturing (AM) is able to generate parts of a quality comparable to those produced through conventional manufacturing, but most of the AM processes are associated with low build speeds, which reduce the overall productivity. This paper evaluates how increasing the powder layer thickness from 20 µm to 80 µm affects the build speed, microstructure and mechanical properties of stainless steel 316L parts that are produced using laser powder bed fusion. A detailed microstructure characterization was performed using scanning electron microscopy, electron backscatter diffraction, and x-ray powder diffraction in conjunction with tensile testing. The results suggest that parts can be fabricated four times faster with tensile strengths comparable to those obtained using standard process parameters. In either case, nominal relative density of > 99.9% is obtained but with the 80 µm layer thickness presenting some lack of fusion defects, which resulted in a reduced elongation to fracture. Still, acceptable yield strength and ultimate tensile strength values of 464 MPa and 605 MPa were obtained, and the average elongation to fracture was 44%, indicating that desirable properties can be achieved.

Influences of Process Parameters on the Microstructure and Mechanical Properties of CoCrFeNiTi Based High-Entropy Alloy in a Laser Powder Bed Fusion Process

“…A large pore existed in the microstructure of the specimen fabricated at E = 333 J/mm 3 (c). The effect of energy density on the density of specimens was investigated previously [44,[46][47][48], and a similar tendency reported.…”

“…Thus, the fracture surfaces of the specimens corresponded well with the grain size and shape of the specimens. [46]. The local misorientation range was set between 0 • and 5 • .…”

“…According to Ghayoor et al [41], at low energy density, the combined effect of the local change in the direction of heat flux due to defects and the Marangoni convection in the meltpool, led to a greater collision of grains, resulting in a fine grain size, whereas at high energy density, the heat flow combined with sufficient time to solidify led to the preferred orientation and larger columnar grains. In general, the orientation of the grain is essentially affected by the direction of the heat flow [41][42][43][44][45][46].…”

“…The (volumetric) energy density, E, which is one of the important process parameters, affects the microstructure remarkably, for instance, grain size and grain growth. The increase in energy density results in grain growth direction aligned with build direction [41][42][43][44][45] and decreased porosity [44,[46][47][48]. However, the energy density poorly predicts the melt pool behavior, as reported as a limitation of energy density as a process parameter, according to Bertoli et al [49,50].…”

“…The Kernel average misorientation (KAM) maps of the xy section of the tensile test specimens before the tensile test fabricated in the direction of 0 • , 45 • , and 90 • are depicted in Figure 15. The KAM map, which proved the local misorientation in the specimens, was used to indicate local strain[46]. The local misorientation range was set between 0 • and 5 • .…”