Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel

Abstract

In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO2 laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO2 laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.

Development and Validation of Empirical Models to Predict Metal Additively Manufactured Part Density and Surface Roughness from Powder Characteristics

“…In this process, shown in Figure 1, a metal powder is melted and fused selectively by a laser system in a layer-by-layer manner to build a component from the bottom up. The powder used in the L-PBF process is typically manufactured by atomisation and has a particle size in the range of 10 to 80 µm in diameter [2]. During the L-PBF process, the laser selectively melts regions of the powder bed; any powder that is not melted in this process can be re-used for subsequent builds using recycling and rejuvenation methodologies.…”

Investigation of Spatter Trajectories in an SLM Build Chamber under Argon Gas Flow

“…Considering that the SLM machines typically operate over a few days to build the desired parts, any non-uniformities in inert gas distribution and other non-idealities introduced due to spatter deposition end up reducing the final product quality. The issues of porosity, residual stresses coupled with the thermal history of the part lead to uncertainties in the properties of parts built using additive manufacturing techniques and are a significant barrier to its widespread adoption [5]. Therefore, any effort that can reduce standard deviation in parameters quantifying product quality is crucial [6].…”

Fatigue Behavior of Additively Manufactured Stainless Steel 316L

“…In its powder form, 316L is also very appropriate for Additive Manufacturing (AM), and out of the different metals suitable for AM, 316L is one of the most commonly used because of its low thermal conductivity and high melting point, combined with limited sensitivity to the presence of oxygen and high absorptivity in infrared [3]. AM actually encompasses a large number of technologies, whose working principles and manufacturing steps may vary substantially and it is well recognized that AM metals exhibit a peculiar microstructure, which is significantly different when compared with nominally equivalent alloys obtained with traditional routes [4,5].…”

“…Overall, the current literature shows that AM 316L can match, or even exceed, tensile properties of conventionally manufactured counterparts, but data still present some variability, depending on the printing method and on the processing parameters. PBF and DED allow the production of dense parts with higher Yield Strength (YS) and Ultimate Tensile Strength (UTS) than BJ and FFF, whereas sintering-based technologies seem to exhibit somewhat higher strain at failure (ε R ) [3,[12][13][14][15].…”