Article
Comparison of Different Additive Manufacturing Methods for
316L Stainless Steel
Javier Bedmar , Ainhoa Riquelme , Pilar Rodrigo , Belen Torres and Joaquin Rams *
Citation: Bedmar, J.; Riquelme, A.;
Rodrigo, P.; Torres, B.; Rams, J.
Comparison of Different Additive
Manufacturing Methods for 316L
Stainless Steel. Materials 2021, 14,
6504. https://doi.org/10.3390/
ma14216504
Academic Editor: Ludwig Cardon
Received: 23 September 2021
Accepted: 25 October 2021
Published: 29 October 2021
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4.0/).
Department of Applied Mathematics, Materials Science and Engineering and Electronics Technology,
Escuela Superior de Ciencias Experimentales y Tecnología (ESCET), Universidad Rey Juan Carlos, Mostoles,
28933 Madrid, Spain; javier.bedmar@urjc.es (J.B.); ainhoa.riquelme.aguado@urjc.es (A.R.);
pilar.rodrigo@urjc.es (P.R.); belen.torres@urjc.es (B.T.)
* Correspondence: joaquin.rams@urjc.es
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
CO
2
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 CO
2
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.
Keywords:
selective laser melting; direct laser deposition; additive manufacturing; 316L;
mechanical properties
1. Introduction
Additive manufacturing (AM) of metals comprises a set of techniques that consists
in the fabrication of pieces, layer by layer, from a 3D design. AM has several advantages
over other manufacturing processes, as it allows fabricating components with complex
geometries [
1
], which are not within the reach of conventional techniques [
2
]. Moreover, an
increase in complexity of AM pieces does not increase manufacturing costs, and may even
reduce them. This fact brings the industry closer to manufacturing topologically optimized
pieces, which, together with the absence of molds, reduces the costs of fabrication and
material waste. Another benefit of AM is its ability to personalize products in different
fields, like prototyping in the automotive industry, the aerospace industry, or in jewelry
and biomedical industries, in which the manufacturing of unique pieces for specific cases
is required [
3
]. On the other hand, AM needs a high initial investment, since metal printers
are more expensive than polymer printers due to their complex technology and energy
requirement; they are also more sensitive to the metallic powder used.
In addition, 3D printed metal pieces have characteristic defects that are not present
with other manufacturing techniques. The main problems are the porosity induced by
gaps left due to the powder shape and flow, and the formation of residual stress and large
grain growth caused by the different consecutive processes of melting, remelting, and heat
treatment, caused by layer by layer deposition. Another disadvantage, which is common
in all AM processes, is the presence of a layered structure in the entire manufactured piece
Materials 2021, 14, 6504. https://doi.org/10.3390/ma14216504 https://www.mdpi.com/journal/materials
