Article
Influence of Metallic Powder Characteristics on Extruded
Feedstock Performance for Indirect Additive Manufacturing
Cyril Santos
1,
*, Daniel Gatões
2
, Fábio Cerejo
3
and Maria Teresa Vieira
2
Citation: Santos, C.; Gatões, D.;
Cerejo, F.; Vieira, M.T. Influence of
Metallic Powder Characteristics on
Extruded Feedstock Performance for
Indirect Additive Manufacturing.
Materials 2021, 14, 7136. https://
doi.org/10.3390/ma14237136
Academic Editors: Ludwig Cardon
and Clemens Holzer
Received: 22 October 2021
Accepted: 22 November 2021
Published: 24 November 2021
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4.0/).
1
CDRSP—Centre for Rapid and Sustainable Product Development, Polytechnic Institute of Leiria,
Rua General Norton de Matos, Apartado 4133, 2411-901 Leiria, Portugal
2
CEMMPRE—Centre for Mechanical Engineering, Materials and Processes, University of Coimbra,
Pinhal de Marrocos, 3030-788 Coimbra, Portugal; daniel.gatoes@uc.pt (D.G.);
TERESA.VIEIRA@dem.uc.pt (M.T.V.)
3
IPN—Pedro Nunes Institute, Rua Pedro Nunes, 3030-199 Coimbra, Portugal; phcerejo@gmail.com
* Correspondence: cyril.santos@ipleiria.pt
Abstract:
Material extrusion (MEX) of metallic powder-based filaments has shown great potential
as an additive manufacturing (AM) technology. MEX provides an easy solution as an alternative to
direct additive manufacturing technologies (e.g., Selective Laser Melting, Electron Beam Melting,
Direct Energy Deposition) for problematic metallic powders such as copper, essential due to its
reflectivity and thermal conductivity. MEX, an indirect AM technology, consists of five steps—
optimisation of mixing of metal powder, binder, and additives (feedstock); filament production;
shaping from strands; debinding; sintering. The great challenge in MEX is, undoubtedly, filament
manufacturing for optimal green density, and consequently the best sintered properties. The filament,
to be extrudable, must accomplish at optimal powder volume concentration (CPVC) with good
rheological performance, flexibility, and stiffness. In this study, a feedstock composition (similar
binder, additives, and CPVC; 61 vol. %) of copper powder with three different particle powder
characteristics was selected in order to highlight their role in the final product. The quality of the
filaments, strands, and 3D objects was analysed by micro-CT, highlighting the influence of the
different powder characteristics on the homogeneity and defects of the greens; sintered quality was
also analysed regarding microstructure and hardness. The filament based on particles powder with
D
50
close to 11
µ
m, and straight distribution of particles size showed the best homogeneity and the
lowest defects.
Keywords: additive manufacturing; copper; feedstock; MEX; filament; micro-CT
1. Introduction
Additive manufacturing (AM) has gained a great amount of interest in the past
two decennia for various fields of applications [
1
]. After the boom of direct processes (i.e.,
selective laser melting (SLM), electron beam manufacturing (EBM), direct energy deposition
(DED)), two indirect technologies assume more and more the future (binder Jetting (BJ) and
material extrusion (MEX)), due to their simplicity, reliability, low cost (i.e., equipment) and
a wide range of different printing materials available. The latter is well known, particularly
for polymeric materials, under the name of fused deposition modeling (FDM). When
applied to the mixing of metallic/ceramic powder particles and organic binder and/or
additives based on polymers, it has adopted the standardised name of MEX [
2
–
6
]. This
process for 3D object shaping is based on FDM, but filament manufacturing is similar
to powder metal extrusion process (PEP) and powder injection moulding (PIM). Both
these processes use, as feedstock, polymers and organic materials with the highest feasible
metal powder content, designated by critical powder volume concentration (CPVC) [
7
]. A
feedstock must consist of a powder with optimal characteristics and an appropriate binder,
which are determinant factors to achieve quality in the final 3D object [
8
,
9
]. Similarly to
Materials 2021, 14, 7136. https://doi.org/10.3390/ma14237136 https://www.mdpi.com/journal/materials
