A simple route for additive manufacturing of 316L stainless steel via Fused Filament Fabrication

Abstract

The low-cost material extrusion (MEX) additive manufacturing technology can offer an economical alternative to manufacture me tal parts with complex geometry over traditional manufacturing or the more expensive powder bed fusion (PBF) techniques. In this work, a feedstock made of 316L stainless steel powder (65 % by volume) and a single component binder (LDPE) system was developed. The use of a single bind er rather than two or more components, commonly used in metal MEX, introduces a novel and more sustainable solution in term s of costs and less use of chemicals. The rheology and processability of the feedstocks were studied, and samples were 3D printed. Debinding and sintering under a hydrogen atmosphere at 1380 °C were performed, and the resulting metallic parts have been characterized by a mechanical and microstructural point of view. The results show a sintered steel having 93 % of the theoretical density and an austenitic phase confirming that the post-processing under reductive atmosphere protected the samples from oxidation and other contamination. The sintered 3D parts show a grain size of~45 μm, a yield point of 250 MPa, a tensile strength of 520 MPa, and a Vickers microhardness of 285 HV typical of annealed steel.

Full text

Journal of Manufacturing Processes 67 (2021) 141–150
Available online 1 May 2021
1526-6125/© 2021 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.
A simple route for additive manufacturing of 316L stainless steel via Fused
Filament Fabrication
M. Sadaf, M. Bragaglia *, F. Nanni
University of Rome “Tor Vergata”, Department of Enterprise Engineering “Mario Lucertini”, and INSTM RU Roma-Tor Vergata, via del Politecnico 1, 00133, Rome, Italy
ARTICLE INFO
Keywords:
Fused lament fabrication
Sintering
Stainless steel
ABSTRACT
The low-cost material extrusion (MEX) additive manufacturing technology can offer an economical alternative to
manufacture metal parts with complex geometry over traditional manufacturing or the more expensive powder
bed fusion (PBF) techniques. In this work, a feedstock made of 316L stainless steel powder (65 % by volume) and
a single component binder (LDPE) system was developed. The use of a single binder rather than two or more
components, commonly used in metal MEX, introduces a novel and more sustainable solution in terms of costs
and less use of chemicals. The rheology and processability of the feedstocks were studied, and samples were 3D
printed. Debinding and sintering under a hydrogen atmosphere at 1380 ◦C were performed, and the resulting
metallic parts have been characterized by a mechanical and microstructural point of view. The results show a
sintered steel having 93 % of the theoretical density and an austenitic phase conrming that the post-processing
under reductive atmosphere protected the samples from oxidation and other contamination. The sintered 3D
parts show a grain size of ~ 45
μ
m, a yield point of 250 MPa, a tensile strength of 520 MPa, and a Vickers
microhardness of 285 HV typical of annealed steel.
1. Introduction
Additive Manufacturing (AM) has nowadays induced huge attention.
It is rapidly moving from research to commercial applications because of
its capability to manufacture complex geometric features, which are
difcult or infeasible to develop by traditional machining [1]. Other
remarkable advantages include exceptional design exibility, low ma-
terial wastage, and less production time [2,3]. The most used metal AM
techniques, which make use of metal powder as raw materials, are: se-
lective laser melting (SLM), direct metal laser sintering (DMLS), binder
jetting (BJ), and electron beam melting (EBM) [4,5]. These techniques
nd applications in many engineering sectors such as aerospace, auto-
motive, robotics, and biomedical elds [5,6]. Currently, EBM and DMLS
are the most commercially employed ones, although they still have some
limitations. These processes are very expensive as they need an inert
atmosphere and/or vacuum to avoid oxidation, and high power is
required [7]. Moreover, the 3D printed part must be post-processed [8].
On the other hand, Fused Filament Fabrication (FFF) is one of the
worldwide most commonly used 3D printing techniques [9]. It requires
a very low initial investment and shows a short processing time, low
material wastage, an easy operating system, reasonable control on
processing parameters, and also the possibility to use several materials
simultaneously (multi-material 3D printing) [9–11]. The primary limi-
tations lie in the scarce surface nishing and, more importantly, in the
low operating temperature (deposition temperature is below 500 ◦C),
allowing the use of only polymeric lament or polymer matrix com-
posite laments. However, at present, there are alternative techniques
such as metal injection molding (MIM), in which the feedstock material
composed of a polymer matrix (binder) lled with a high volume of
metallic particles is extruded and injected into a mould cavity to form
the desired shape. The polymer is then removed in a process called
debinding, and then, by a thermal process called sintering operated at a
temperature below the melting temperature of the powder, the fully
densied metallic part is obtained. In view of all the above-reported
considerations, most recently, the metal FFF has been proposed. It in-
volves the preparation of a highly metallic powder-loaded lament,
where the polymeric matrix is a binder (as from the MIM process). The
lament is then 3D printed with a standard FFF printer with the
advantage of producing parts with complex geometry, and the resulting
green body is successively post-processed through debinding and sin-
tering to get a solid metallic part [5]. In the literature, research papers
on the FFF printing by using commercially available 3D printers and
* Corresponding author.
E-mail address: bragaglia@ing.uniroma2.it (M. Bragaglia).
Contents lists available at ScienceDirect
Journal of Manufacturing Processes
journal homepage: www.elsevier.com/locate/manpro
https://doi.org/10.1016/j.jmapro.2021.04.055
Received 24 February 2021; Received in revised form 21 April 2021; Accepted 24 April 2021

Journal of Manufacturing Processes 67 (2021) 141–150
142
more recently using screw-based MEX equipment [12–15] of steels such
as 17-4PH steel [16–19] and 316 L stainless steel [9,20,21] were pro-
posed. Several and very recent researches dealing with the debinding
and sintering of 3D printed samples to obtain the metallic part [22–24]
are available. Furthermore, 3D printer developer companies are moving
towards metal FFF printing; for instance, Desktop Metal started selling
commercial systems employing a one-step debinding process in 2018
[25]. One of the main limitation of the 316 L stainless steel FFF relies in
the size of the printable parts. Safka et al. [26] showed that this issue is
not only related to the printing but also to the post-processing, as during
debinding and sintering printed specimens having walls thicker than 4
mm produced cracks and other defects. Among other metals, copper was
investigated due to its exceptional electrical properties [27], and with
the same principle, ceramics as zirconia [28] and alumina [29] can be
produced. The 3D printing of a metal feedstock is quite complex
compared to unlled or low-loaded polymers (less than 20 % vol). In
fact, in order to obtain dense sintered metals, the ller loading is typi-
cally high, in the range of 55−65 vol % [30], as the metallic particles
have to be very close to allow the sintering process, which involves the
mechanism of diffusion at the surface, lattice, and grain boundary.
However, dealing with highly loaded feedstocks arises some critical is-
sues for the FFF printing:
i) As a general trend, the higher is the ller content, the more brittle
and fragile is the resulting lament. This is a crucial point, as the
lament must have enough stiffness and strength to be easily
manipulated, rolled up in spools, and extruded through the
nozzle during the FFF printing. It was shown [9] that the choice
of the binder systems plays a signicant role in the quality of
laments, changing from highly exible to very brittle. Highly
lled feedstocks based on polypropylene (PP), polyethylene (PE)
binder systems, resulted in high lament exibility, better
printing quality, and high densication in the nal sintered
products.
ii) Melt rheology of the loaded lament. During the printing, the
material is melted and pushed through a nozzle, but the higher
the ller loading, the higher the melt viscosity. Generally, the
viscosity of the material depends on the solid loading, binder
behaviour, temperature, state of agglomeration, and shear rate
[31]. Kukla et al. [32] discussed the effect of particle size on the
physical properties of highly lled 316 L stainless steel feedstocks
for FFF. They concluded that laments made of particles having a
high average size (>50
μ
m) showed less printability due to high
viscosity [33,34].
iii) The dimensional stability of the lament also affects the print-
ability. If the diameter of the lament is lower than the standard
value (i.e., 1.75 mm), the ow rate of melted material is affected
as well as the resulting thickness and widths of the layers, ending
up in poor adhesion among the deposited layers and/or presence
of unwanted voids among adjacent layers. Such defects will not
be eliminated with the sintering and will be kept in the nal metal
piece. On the other hand, if the lament diameter is higher than
the standard value, feeding through the nozzle may be difcult,
and blocking can occur. In any case, an overow of material shall
be expected, resulting in low dimensional accuracy [35,36].
Therefore, it is clear that, despite it is eliminated during the
debinding process, the binder system has a signicant inuence on the
whole manufacturing process, and it has a strong impact on the quality
of the nal products [37]. Typically, in the MIM process, the binder
system is made of: 1) a backbone binder, which is the component that
holds the shape, 2) a second polymer phase (generally a wax) that
guarantees good rheological behaviour, and 3) other additives like sta-
bilizers, compatibilizers, and dispersing agents (i.e., stearic acid) help-
ing to enhance the diffusion among powder-binder, avoiding phase
separation and agglomeration [37–39]. The binder system is typically
removed by solvent and/or thermal debinding [37,40] but also catalytic
debinding, where most of the binder is attacked by a catalytic acid
vapor, is quite a common practice in the MIM process [39,41].The
critical parameters of this process include the choice of an appropriate
solvent, dispersion time, and temperature for solvent debinding; heating
rate, holding time, and furnace atmosphere for thermal debinding [42].
The binder must be entirely removed before the nal step of sintering, as
an incomplete binder removal will lead to the formation of defects that
affect the quality of sintered parts [39]. Many factors lead to incomplete
binder removal, among which the most relevant ones are the incorrect
debinding temperature, the wrong heating rate, and /or insufcient
holding time [37]. Thermal debinding defects are frequently seen when
the applied heating rate is too fast. In most cases, the defects are caused
by the fast decomposition of the binder components. It has been dis-
cussed for 316 L stainless steel [22] how a low debinding rate may help
remove the binders out of 3D printed parts, resulting in defect-free
sintered samples. Another critical factor is the debinding atmosphere.
As stainless-steel powder is easily oxidized at a high temperature, a
vacuum or a controlled atmosphere furnace is generally used to prevent
oxidation. In [43], debinding of 316 L stainless steel was carried out in a
non-reactive gas (i.e., Argon; Nitrogen), as well as in a reductive at-
mosphere (i.e., Hydrogen) oven. However, an inert gas may lead to
undesirable carbon product formation during the thermal degradation
of the binder system, which may originate unexpected melting at
elevated temperatures during sintering [44]. The presence of carbon
may further induce the precipitation of carbides at the grain boundaries
during cooling. Moreover, a nitrogen-based atmosphere enhances the
mechanical properties with the risk of decreasing the corrosion perfor-
mance. The presence of nitrogen in the atmosphere can produce nitro-
gen absorption, leading to chromium nitride (Cr
2
N) precipitation,
especially in the range of 500–600 ◦C with the consequent chromium
depletion and deterioration of corrosion resistance. The appropriate
pressure and ow rate of the gas must be maintained to prevent air
contamination [45]. A carbon content above 0.06 % in 316 L steel leads
to large pores and less corrosion resistance [46]. Some authors suggest
the use of air atmosphere during debinding to overcome this problem
[44]. Also, the gas ow rate affects the debinding; if not sufcient, it
inhibits the binder evaporation allowing the binders to be retained in the
brown parts. Consequently, cracks formation, blistering, bloating, and
extensive internal voids due to incomplete removal during sintering can
show up [43]. After debinding, sintering has to be performed. Sintering
is the thermal treatment (performed at 70–90 % of the melting point of
metal powder) to consolidate and bond the loose particles into a dense
coherent body [47]. During sintering, powder particles form coherent
bonds and densify by pore shrinkage. Sintering time and temperature
are the most signicant factors from a practical perspective. Other
relevant parameters are heating and cooling rate, sintering atmosphere,
particle size, and geometry [43]. Increasing the sintering temperature
and the holding time leads to a decrease of the porosity, resulting in an
enhancement of the density; however, at the same time, it induces the
increase of the grain size, inuencing hardness and mechanical strength.
It has been shown that sintering temperature is more inuential than
sintering time on grain size [48]. Inadequate sintering produces parts
with inferior mechanical properties and low corrosion resistance.
Insufciently sintered parts show poor bonding, original particle
boundaries, sharp pores, and a high concentration of interstitials (car-
bon and oxygen) [49]. Mechanical properties are also inuenced by the
cooling rate. In particular, controlling the cooling rate from the sintering
temperature to ~500 ◦C, plays a vital role in avoiding re-oxidation,
nitride formation, and carbide formation that affects ductility and
corrosion resistance [50].
The aim of this work is to develop laments of highly loaded 316 L
stainless steel particles that can be successfully 3D printed via a low-cost
FFF technique and later sintered as metallic parts. A very simple binder
consisting of only low-density polyethylene (LDPE) was used, avoiding
the necessity to perform solvent debinding and opening the possibility to
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
143
use recycled LDPE in view of a low environmental impact process. The
3D printed parts have been thermally treated, allowing binder removal
and sintering. The resulting metallic parts have been characterized from
a morphological, microstructural, and mechanical point of view.
2. Materials and methods
2.1. Raw materials and preliminary characterizations
The feedstock developed in this research was composed of spherical
gas atomized 316 L stainless steel powder supplied by H¨
ogan¨
as (AM 316
L 20−53
μ
m, nitrogen gas atomized, content of Carbon (C) 0.018 %), as
a metallic ller. The particle size distribution data measured by the
producer is shown in Table 1. A low-density polyethylene (LDPE
RIBLENE MV 10 R ENI Versalis) purchased by PowderEx [51] was used as
an organic binder. Both powders were used as received with no further
treatment.
Preliminary characterization has been performed on raw materials.
The phase analysis of 316 L stainless steel powder was investigated by X-
ray diffraction (XRD, Philips X’Pert 1710, Amsterdam, Netherlands). XRD
patterns were recorded in the 2θ range 10–90◦in the following condi-
tions: Cu K
α
radiation (λ =1.5408 Å), 40 kV and 40 mA, step size =
0.020◦, time per step =2 s. The morphology of the 316 L stainless steel
particles was analyzed by scanning electron microscopy (Zeiss SEM-FEG
Leo, supra-35, Oberkochen, Germany) coupled with energy dispersive
spectroscopy (EDS) (INCA x-sight, Oxford Instruments, Abingdon, United
Kingdom). Fourier transform infrared spectroscopy (FT-IR) was per-
formed on LDPE powder using an FTIR spectrometer (Perkin Elmer 100,
Waltham, Massachusetts, United States of America). The spectra were ac-
quired in the range of 4000-400 cm
−1
, with 4 cm
−1
resolution, and each
spectrum averaged over 32 scans. Melt Flow Indexer (MFI) (MFI, Tinius
Olsen, MP1200M-USA, Horsham, United States of America) was used to
analyse the ow properties of LDPE accordingly to ASTM D1238 stan-
dard. The test was carried out at 190 ◦C with a weight of 2.16 kg.
2.2. Feedstock development and rheological characterization
The feedstock formulation used in this research was composed of 65
% by volume of 316 L stainless steel and 35 % vol of LDPE as a binder.
The feedstock (one batch having a volume of 170 cm
3
) was compounded
in a kneader with a counter-rotating roller (Brabender GmbH & Co. KG,
Duisburg, Germany) at a temperature of 170 ◦C, kneading time of 30 min,
and rotational speed was set at 50 rpm. After compounding, the feed-
stock has been mechanically grounded (1−3 mm) and dried in the oven
at 50 ◦C for 24 h. The rheological test on feedstock was performed by a
rheometer (RPA 2000, Alpha Technologies, Hudson, United States of
America) using a cone-cone geometry. Measurements of viscosity were
performed in temperature sweep conguration in the range 110−230 ◦C
at a frequency of 1 Hz; an unlled LDPE was tested as a reference.
2.3. Filaments extrusion and 3D printing
Production of laments based on feedstocks was performed in a
single screw extruder (FILABOT EX2, Filabot, Barre, United States of
America) with a nozzle diameter of 1.75 mm. Filaments were extruded at
a temperature of 155 ◦C, a speed of 15 rpm, and coiled in spools. Fila-
ments were mechanically tested performing tensile test using a universal
testing machine (Lloyd LRX, AMETEK, Inc., Berwyn, Pennsylvania, United
States of America) equipped with a 500 N load cell, crosshead speed 5
mm/min at room temperature. Parallelepipeds with different di-
mensions (i.e., 35 ×20 ×6.5 mm
3
and 20 ×20 ×5 mm
3
) and Type V
tensile test specimens (having dimension 63.5 ×3.18 ×3.5 mm
3
ac-
cording to ASTM D638) were printed by the FFF. Printing was conducted
on Zmorph 2S (Zmorph S.A, Wrocław, Poland) FFF machine. The software
Voxelizer was used to slice the parts and to create the G-code for printing
with the following parameters: nozzle head temperature 220 ◦C, bed
temperature 60 ◦C, nozzle diameter 0.6 mm, layer height 0.2 mm, inll
100 %, rectilinear raster angle (0−90◦), printing speed of 80 mm/s, and
two perimeter lines. Specic xative for 3D printing (Dimax) was
applied to the glass printer bed for increasing adhesion during the
production of 3D parts. Both produced laments and 3D printed samples
have been stored in a vacuum desiccator prior to use.
2.4. D printed parts characterization
Thermogravimetric Analysis (Perkin Elmer Pyris 1 TGA, Waltham,
Massachusetts, United States of America) was performed on the 3D printed
sample to estimate the temperature range of the debinding. The analysis
was performed in a nitrogen atmosphere (40 mL/min) in the tempera-
ture range 25 ◦C–700 ◦C with a heating rate of 10 ◦C/min.
2.5. Thermal debinding and sintering
Thermal debinding of 3D printed samples was performed in a furnace
(Elnik MIM 301 Lab Furnace, Elnik, Cedar Grove, NJ, United States of
America) in a hydrogen atmosphere (H
2
partial pressure 0.4 bar) at 500 ◦C
for 90 min. Sintering was performed at 1380 ◦C for 180 min. The heating
rate of 5 ◦C/min was kept constant for both debinding and sintering. The
thermal cycle is reported in Fig. 1.
2.6. Sintered 3D printed parts characterizations
Density measurements were performed, according to ASTM D79,
using a buoyancy method-based pycnometer (Sartorius, G¨
ottingen, Ger-
many) which allows for the determination of density by applying
Archimedes’ Principle. Mean density values were taken from at least
three measurements for each specimen. Sintered 3D printed samples
have been cut using a diamond saw (Buheler Isomet 4000, Buheler, Lake
Bluff, Illinois, United States of America), samples have been cold- mounted
in epoxy resin (Epoglass, curing time of 3 h at 60 ◦C) and mechanically
Table 1
Particle size distribution of 316L stainless steel powder
from Sieve analysis as declared by H¨
ogan¨
as [52].
Particle Size (
μ
m) Distribution
(%)
<20
>20
>36
>45
>53
>63
6.96
47.17
22.96
16.80
6.03
0.08
Fig. 1. Thermal cycle of debinding and sintering in a hydrogen atmosphere.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
144
ground and polished using silicon carbide (SiC) papers and diamond
suspension up to 3
μ
m, then washed in an ultrasonic bath of ethanol. A
chemical etching of aqua regia (consisting of hydrochloric acid, nitric
acid, and ethanol solution in the volume ratio 3: 1: 1) was performed to
reveal the grain structure. The etched surface morphology was investi-
gated using optical microscopy (Nikon Epiphot TME, Nikon Corporation,
Tokyo, Japan) coupled with an acquisition camera (Visicam 10.0, VWR-
Avantor, Radnor, Pennsylvania, United States of America). Image analysis
was performed by ImageJ software, allowing to calculate the grain size
and the porosity. The grain size was evaluated according to ASTM E112-
13 using the intercept method. Electron microscopy (SEM Leo Supra
Zeiss) and EDX were also performed. The phase analysis of sintered 3D
printed samples has been performed through X-ray diffraction (XRD,
Philips X’Pert 1710) in the 2θ range 10–90◦in the following conditions:
Cu K
α
radiation (λ =1.5408 Å), 40 kV and 40 mA, step size =0.020◦,
time per step =2 s. Mechanical properties have been analysed by per-
forming a tensile test according to ASTM E8/E8M-16a using a universal
testing machine (Instron 5569, Instron, Norwood, Massachusetts, United
States of America) with a crosshead speed of 5 mm/min. According to the
Hall-Petch equation, the yield point was also estimated, as shown in Eq.
(1). Whereas ˝
σ
y˝is the yield strength of polycrystalline metals, “d” the
average grain diameter and ˝
σ
o˝and ˝ks˝are constants for the metal. At
a 0.2 % strain, the value of
σ
o is 164 MPa and ks is 621.4 MPa
μ
m
1/2
for
316 L austenitic stainless steel at room temperature [53,54].
σ
y=
σ
o+ks/(̅̅̅
d
√)(1)
Micro-hardness test (ASTM Standard E92) using Vickers indenter
(Future Tech FM-700, Future Tech Corp., Kawasaki, Japan) by applying a
load of 500 g for 30 s was performed along the cross-section of mounted
sintered steel sample. Ten measurements were performed on each
sample.
3. Results and discussion
3.1. Results of raw materials characterization
At rst, the as-received gas atomized stainless-steel 316 L powder
was fully characterized in terms of morphology, chemical composition,
and microstructure. SEM images of the powder are shown in Fig. 2a) and
b). Most of the particles show a spherical or quasi-spherical morphology,
with very few inclusions of non-spherical ones in the batch of powder
and few satellite particles that have to be ascribed to the gas atomization
process [55]. The average particle size is 33
μ
m, in good agreement with
the datasheet where the total percentage of particles greater than 53
μ
m
and less than 20
μ
m is 5% [52]. The EDX analysis (Fig. 2d) highlights the
typical composition of the as-received state of 316 L stainless steel. In
addition to the iron (Fe) peak, 19 % of chromium (Cr) and 11 % of nickel
(Ni) elements were detected. Accordingly, to the datasheet and the
chemical composition of 316 steel, 1.75 % of Manganese (Mn), 1.4 % of
molybdenum (Mo), and 1.1 % of silicon (Si) were also revealed in the
alloy.
The X-ray diffraction pattern of the 316 L stainless steel powder
presented in Fig. 2c) shows sharp peaks at 2θ =43◦, 53◦and 74◦indi-
cating a face-centered cubic structure, representing the random oriented
crystalline phase of austenitic Fe-Cr-Ni alloy as conrmed by the JCPDS
card (3303-97).
The as purchased LDPE binder was analysed by means of FT-IR. The
spectra (Fig. 3a) show a peak at 3451 cm
−1
corresponding to the
stretching vibration of the OH group, which is ascribed to the presence
Fig. 2. a) SEM image of 316L stainless steel powder with magnifying power of 250 X; b) SEM image of 316L stainless steel powder with magnifying power of 5000 X;
c) XRD pattern of the 316L stainless steel powder in the 2θ range 10–90
◦; d) EDX analysis of the steel particles.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
145
of moisture. The other sharp peaks at 2918 and 2848 cm
−1
due to CH
2
stretching. The peaks of 1464 and 722 cm
−1
arise from the skeletal vi-
brations of CH
2
.
The melt ow index (MFI) of LDPE at 190 ◦C with a 2.16 Kg load was
55.2 g/10 min. The MFI value indicated a very good owability of the
chosen binder. This is important in view of both lament preparation
and FFF printability.
3.2. Feedstock rheology and 3D printing
The viscosity measured by the rheological test of the developed
feedstock in the range of 110−230 ◦C is shown in Fig. 3b) and compared
to that of the LDPE unlled polymer. As expected, the feedstock sample
evidenced higher viscosity than the neat LDPE due to high ller-ller
interaction. Feedstock viscosity is highly inuenced by temperature
too, as it varies in the range 10
3
-10
5
Pa s at increasing temperature. The
viscosity of the feedstock plays a signicant role throughout the extru-
sion of the material in the FFF printing, as the laments should act as a
piston to create the continuous ow of the molten compound during
extrusion [56]. It is imperative that suitable viscosity is reached in the
nozzle in order to guarantee the proper rheological behaviour of the
melted feedstock, allowing it to be attened and deposited to the bottom
plate in the layer-by-layer piece growing. According to the literature, the
values of the viscosity of the feedstock suitable for FFF printing should
lie in the range 10
2
-10
5
Pa s [57,58]. From the rheological curve, a
nozzle temperature of 220 ◦C was chosen for the printing, as it was
deemed to be sufcient to guarantee the correct owability. Examples of
extruded laments and 3D printed parts are shown in Fig. 4. The
Fig. 3. a) FTIR spectra of Low-Density Polyethylene binder (LDPE) in the range of 4000–400 cm
−1
, with 4 cm
−1
resolution; b) Viscosity of the neat LDPE (dotted line)
and feedstock (dashed symbol) in the range of 110–230 ◦C at a frequency of 1 Hz. (For interpretation of the references to colour in this gure legend, the reader is
referred to the web version of this article).
Fig. 4. a) 316L loaded extruded lament; b) parts produced by FFF; c) 3D printed dog-bone specimen and d) Stress-strain curves of 316L loaded extruded laments.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
146
lament presents a constant diameter (diameter =1.75 mm ±0.1 mm),
and the stress-strain curves, displayed in Fig. 4d), show a brittle
behaviour. Nevertheless, the mechanical properties of lament (i.e.,
σ
max
=3.22 ±0. 15 MPa and
ε
max
=2.4 %) are comparable with other
laments available in the literature [37] and enough to guarantee a
proper feeding of the 3D printer. During printing, overow and under-
ow issues were not recorded. The appearance of the printed parts was
good, and no printing defects were visible (Fig. 4b).
Fig. 5 shows the SEM morphology of the 3D printed part surfaces. A
very good dispersion of the ller throughout the sample is appreciable.
The stainless-steel particles are well bonded and covered by the matrix
polymer. Such a type of bonding morphology in the green part is
required to operate the processing of debinding and sintering without
disturbing the shape of the printed parts.
Fig. 5a) highlights the layer-wise structure of the samples as well as
some porosity in a few spots (pointed in yellow circles) between the
adjacent layers. In particular, gaps between adjacent roads (intra-layer
voids) and/or subsequent layers (inter-layer voids) are visible. The
presence of porosity in specimens manufactured by FFF is an unfortu-
nately intrinsic drawback of this technique. In fact, during printing, the
bonding process is driven by the residual thermal energy in the material
after deposition. The adhesion/cohesion between new and previously
deposited layers can be activated by polymer chains diffusion across the
interface. This phenomenon of coalescence is driven by viscous ow and
is inuenced by viscosity, temperature, surface tension, road geometry,
and thermal mismatch between deposited material [59,60]. If the
porosity is too high, it is well known to cause not full densication [53]
and lower mechanical properties of the sintered part [16,23].
3.3. Thermogravimetric Analysis (TGA), debinding and sintering
Thermogravimetric Analysis (TGA) was performed on the feedstock
to set debinding. TGA under the nitrogen atmosphere of the feedstock
sample and neat LDPE binder are shown and compared in Fig. 6a). The
mass loss curve of both binder and feedstock shows one-step degrada-
tion, which is in agreement with the decomposition of LDPE ascribed to
the random scission of the chains and the formation of free radical [61,
62]. The decomposition temperature of neat LDPE, taken as the mini-
mum weight derivative curve, is 418 ◦C while the feedstock decompo-
sition temperature is 492 ◦C as the presence of the metallic ller
enhances the thermal stability, according to the literature [63]. The
polymer completely degraded at 500 ◦C, and the actual content of steel
powder, evaluated by measuring the residual weight percentage (R) of
TGA curves, is 94.5 % and is in good agreement with the theoretical
ller content of 94.2 % by weight. Thus, thermal debinding was set at
500 ◦C with a heating rate of 5 ◦C/min for 90 min in a controlled
oxygen-free atmosphere (H
2
partial pressure 0.4 bar).
TGA was then performed on the debound sample too (Fig. 6b)), to
verify the presence, if any, of residual polymer. No mass loss (black
curve) was recorded at increasing temperature. This result and together
with the SEM analysis of surfaces (Fig. 6c) and d)), nally conrmed that
the binder was fully removed in the thermal treatment. This was an
excellent result, as in the literature, it is reported that the use of a single
binder component (LDPE) could have made the debinding process
critical. In particular, during the initial stages, some defects like
cracking, bloating could form due to the stresses applied by the trapped
gas originating by the decomposition of the binder. In our case, even if
the binder was composed of one single component, the degradation
process was successfully conducted on all the investigated samples, and
no trapped gas was revealed since the heating rate was slow enough,
allowing the proper evaporation of the polymer. Moreover, the presence
of some intrinsic porosity due to the 3D printing process may have acted
as a “relief valve” for the correct release of volatile products from the
binder thermal degradation. After debinding, the steel particles appear
to be in contact with each other (Fig. 6d). This is an essential aspect as
the rst sintering stage is the necking formation between two adjacent
particles. Heat is the driving force, it enhances atoms vibration, and the
mass transport occurs mainly by surface transport mechanisms (i.e.
evaporation and condensation, surface diffusion, and volume diffusion)
[64]. The atoms move from the surface of the particles to the point of
contact of the particles. As the bond between particles increases, causing
the formation and some growth of the neck between the two particles.
Then the formed necks begin to grow [65]. If the particles are not in
good contact, this process fails.
3.4. Sintered 3D printed samples: morphology, phase analysis and
mechanical properties
3D printed samples before and after sintering are presented in Fig. 7.
It is possible to notice the shrinkage occurring after the sintering, with
reduction of the dimensions of the samples (i.e., 3D printed parallele-
piped sample dimensions were 35 ×20 ×6.5 mm
3
and resulted in 31.1
×17.8 ×5.5 mm
3
sintered sample (Fig. 7b)) while 3D printed tensile
specimen dimensions were 63.5 ×3.2 ×3.5 mm
3
resulting in 56.5 ×
2.85 ×2.95 mm
3
sintered sample dimensions. Shrinkage is the result of
the elimination of pores in the green body, being the driving force the
bulk transport mechanisms [65]. In particular, plastic ow, viscous ow,
grain boundary diffusion, and volume diffusion occur [66]. The
shrinkage was not isotropic as it was 11 % in the X direction and the Y
direction, and 15 % in the Z direction. Literature reports an approximate
14 % linear (X direction) shrinkage for a 65 % volume fraction 316 L,
assuming the powder fully densies [67].As our samples shrank only 11
% in the X direction, it must be assumed that some porosity remained.
After sintering, no presence of eye-visible defects (i.e., surface cracks
or blistering) was observed. The diffraction pattern of sintered stainless-
steel samples, displayed in Fig. 8a), highlights the presence of the
austenitic crystalline phase of Fe-Cr-Ni alloy (JCPDS 33-0397), con-
rming that no chemical and phase changes occurred during the whole
Fig. 5. a) SEM image of green part surface (XY printing plane) with magnifying power of 200 X, b) SEM image of green part with magnifying power of 1000 X.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
147
process. No other peaks ascribable to other phases have been detected,
indicating the reductive hydrogen atmosphere (H
2
partial pressure 0.4
bar) protected the samples from oxidation and other contamination
[68]. The metallographic analysis of the etched sample surface (Fig. 8b)
and c)) revealed a well-densied austenitic grain structure. The equi-
axed grains have a regular mean dimension of 45 ±5
μ
m. The
microstructure is typical for an annealed austenitic steel as the sintering
temperature is higher than recrystallization temperature allowing grain
growth, furthermore the uncontrolled cooling process is very slow (1–2
◦C/ min), and the grain growth can go on during cooling until the
recrystallization temperature is reached. The EDX analysis (Fig. 8d),
performed on the sintered stainless-steel component, revealed that the
Fig. 6. a) Thermogravimetric Analysis (TGA) of LDPE and 3D printed part; b) TGA mass loss of 3D printed sample before and after debinding; c) SEM image of
debound part with magnifying power of 100 X; d) SEM image of debound sample at 5000X.
Fig. 7. a) Sintered 316L stainless steel 3D printed part; b) comparison of sintered sample with 3D printed green part.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
148
elemental composition remained the same after the thermal treatment.
By image analysis some intergranular porosity is appreciable. The
porosity attained by image analysis of the sintered steel resulted in 7%.
This value is in agreement with the result obtained with the density
measurements displayed in Table 2. According to these results, the
densication after sintering is in the range of 91–93 % which is com-
parable to the values generally obtained with samples produced via MIM
[69].
The shape and type of porosities can provide information on the
cause determining it. If the porosity is non-spherical, it is probably a
process-induced (FFF printing) porosity, while if it is spherical, it is
connected to thermal treatment (debinding) [4,23,70]. In our case, the
non-spherical pores can be related to defects produced during 3D
printing, as already discussed in the morphology of 3D printed sample,
and are expected to inuence the resulting mechanical properties, such
as tensile strength and microhardness [23,71]. The representative
stress-strain curves of sintered samples are displayed in Fig. 9, while the
mechanical properties are reported in Table 2. The samples show ductile
behaviour. A mean yield point of 252 MPa and a mean tensile strength of
520 MPa were recorded. Both the yield and the tensile strength values
are lower than those obtained by using other manufacturing techniques
(i.e., SLM) as shown in Table 2. In particular, the lower yield strength
and ultimate tensile strength must be ascribed to the high sintering
temperature (resulting in high grains size) and to the presence of
porosity. Porous materials can be considered as two-phase composites in
which the pores act as a null strength dispersed phase. The pores size,
geometrical shape, spatial arrangement, and orientation inuence the
mechanical response of the piece. In particular, the UTS of our samples is
affected by porosity presence according to the model presented by Ji and
Xia [72]. The 7% porosity results in a UTS of about 80 % of the fully
Fig. 8. a) XRD of sintered 3D printed sample; b) Optical micrograph 400 X of etched sintered sample; c) SEM micrograph of etched sample and d) EDX analysis of the
sintered part.
Table 2
Mechanical properties of sintered samples and comparison with other manufacturing techniques.
Sample Process Yield strength
[MPa]
Tensile strength
[MPa]
Elastic modulus
[GPa]
Micro-hardness
[HV]
Densication (%)
This work FFF 252 ±7 521 ±16 198 285.5 ±5.5 93
Gong et. al. [5] FFF 167 465 152 n.d. 98.5
Poszvek et al. [21] FFF 234−251 521−561 n.d. n.d. n.d.
Thompson et al. [22] FFF 500 * 900 * n.d. n.d. 95
Damon et al. [23] FFF 155−165 500−520 210 n.d. 98.3−99.5
Hitzler et al. [5] SLM 590 700 227.3 223−245 >99
Rottger et al. [75] SLM 208.8−469.6 486.4−644.3 141−205 n.d. >99.3
Omar et al. [69] MIM n.d. >500 n.d. >200 91.5−93
Zhang et al. [74] MIM 170−205 460−560 n.d. n.d. 98.5
Heaney et al. [76] MIM n.d. 527−590 n.d. n.d. 97.7−99.1
*
Tensile strength and yield strength calculated from three point bending test.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
149
densied 316 L UTS reported in the literature [73].
On the other hand, the calculated yield strength of the sintered 3D
printed steel, by applying the Hall-Petch’s equation without considering
the porosity presence, resulted to be 260 MPa, once again higher than
the experimental results and has to be ascribed to porosity. Nonetheless,
the obtained results are in good accordance with the mechanical resis-
tance offered by MIM stainless steel parts sintered at a lower tempera-
tures [74].
A mean Vickers microhardness value of 285.5 ±5.5 HV was
accomplished. This result is also in agreement with other works where
the HV values on MIM 316 L stainless steel were in the range 250−290
HV [69,77]. Thermal treatments (i.e., quenching) or cold working (i.e.,
shoot peening) could be applied as post-processing to modify the grain
size and/or the microstructure to increase the mechanical properties.
4. Conclusion
In this work, highly loaded laments based on a single-component
binder (LDPE) and 316 L stainless steel powder were produced. Speci-
mens of various shapes were successfully printed through FFF. Using a
single-component binder allows for a more sustainable solution in terms
of costs and less use of chemicals, opening the possibility of using
recycled polymer as a binder. During debinding, a low heating rate of 5
◦C/min was the key feature, allowing the volatilization of degraded
polymers, and maintaining the shape without developing surface de-
fects. Final densication and pore elimination were achieved by sin-
tering at 1380 ◦C for 180 min. Densication of 93 % was recorded in the
sintered samples. The phase analysis revealed only the presence of
austenitic phase, conrming the post-processing under reductive
hydrogen atmosphere protected the samples from oxidation and other
contamination. Microstructure analysis highlights a well-densied grain
structure of austenitic having a regular dimension of 45 ±5 microns,
and the elemental composition remained the same during the entire
thermal treatment. The produced sintered parts have yield strength of ~
250 MPa, a tensile strength of 520 MPa, and a Vickers microhardness of
285.5 HV. The results of the mechanical tests evidence that the FFF
printed and sintered material are comparable to MIM products even if
the presence of porosity due to the FFF process affects the resulting
mechanical properties. This result opens a new perspective in the real-
ization of low-cost complex steel parts.
Declaration of Competing Interest
The authors declare that they have no known competing nancial
interests or personal relationships that could have appeared to inuence
the work reported in this paper.
Acknowledgement
The authors wish to thank H¨
ogan¨
as AB for kindly providing the 316L
stainless steel powder used in this research.
References
[1] Huang SH, Liu P, Mokasdar A, Hou L. Additive manufacturing and its societal
impact: a literature review. Int J Adv Manuf Technol 2013;67:1191–203. https://
doi.org/10.1007/s00170-012-4558-5.
[2] Gibson I, Shi D. Material properties and fabrication parameters in selective laser
sintering process. Rapid Prototyp J 1997;3:129–36. https://doi.org/10.1108/
13552549710191836.
[3] Palmero EM, Casaleiz D, De Vicente J, Hern´
andez-vicen J, L´
opez-vidal S, Ramiro E,
et al. Composites based on metallic particles and tuned lling factor for 3D-
printing by Fused Deposition Modeling. Compos Part A Appl Sci Manuf 2019;124:
105497. https://doi.org/10.1016/j.compositesa.2019.105497.
[4] Sames WJ, List FA, Pannala S, Dehoff RR, Babu SS. The metallurgy and processing
science of metal additive manufacturing. Int Mater Rev 2016;61:315–60. https://
doi.org/10.1080/09506608.2015.1116649.
[5] Gong H, Snelling D, Kardel K, Carrano A. Comparison of stainless steel 316L parts
made by FDM- and SLM-based additive manufacturing processes. Solid Free Fabr
2019;71:880–5. https://doi.org/10.1007/s11837-018-3207-3.
[6] DebRoy T, Wei HL, Zuback JS, Mukherjee T, Elmer JW, Milewski JO, et al. Additive
manufacturing of metallic components – process, structure and properties. Prog
Mater Sci 2018;92:112–224. https://doi.org/10.1016/J.PMATSCI.2017.10.001.
[7] Ren Luquan, Zhou Xueli, Song Zhengyi, Zhao Che, Liu Qingping, Xue Jingze, et al.
Process parameter optimization of extrusion-based 3D metal printing utilizing
PW–LDPE–SA binder system. Materials (Basel) 2017;10:305–29. https://doi.org/
10.3390/ma10030305.
[8] Bandyopadhyay A, Zhang Y, Bose S. Recent developments in metal additive
manufacturing. Curr Opin Chem Eng 2020;28:96–104. https://doi.org/10.1016/j.
coche.2020.03.001.
[9] Riecker S, Hein S, Studnitzky T. 3D printing of metal parts by means of fused
lament fabrication-A non beam-based approach. Eur. 2017– AM Altern. Technol..
2017.
[10] Andersen O, Riecker S, Studnitzky T, Hein S, Lohse U, Kie- B. Manufacturing and
properties of metal parts made by fused lament fabrication. Powder Metall 2018;
18:2–7.
[11] Masood SH. Advances in fused deposition modeling. Compr. Mater. Process. 2014;
10:69–91. https://doi.org/10.1016/B978-0-08-096532-1.01002-5.
[12] Drotman DTJ. Design of a screw extruder for additive manufacturing. 2015.
[13] Lengauer W, Duretek I, Fürst M, Schwarz V, Gonzalez-Gutierrez J, Schuschnigg S,
et al. Fabrication and properties of extrusion-based 3D-printed hardmetal and
cermet components. Int J Refract Met Hard Mater 2019;82:141–9. https://doi.org/
10.1016/j.ijrmhm.2019.04.011.
[14] Lieberwirth Clemens, Harder Arne, Seitz Hermann. Extrusion based additive
manufacturing of metal parts. J Mech Eng Autom 2017;7:79–83. https://doi.org/
10.17265/2159-5275/2017.02.004.
[15] Kniffka Wieland, Eichmann Michael, Witt Gerd, Clemens Lieberwirth HS. Additive
Fertigung mit Metallspritzguss-Granulaten / Additive manufacturing with metal
injection molding granules. 2016. https://doi.org/10.3139/9783446450608.022.
[16] Godec D, Cano S, Holzer C. Optimization of the 3D printing parameters for tensile
properties of specimens produced by fused lament fabrication of 17-4PH stainless
steel. Materials (Basel) 2020;13:774–98. https://doi.org/10.3390/ma13030774.
[17] Gonzalez-gutierrez J, Godec D. 3D printing conditions determination for feedstock
used in fused lament fabrication of 17-4PH stainless steel parts. Metalurgija 2017;
57(1-2):117–20.
[18] Galati M, Minetola P. Analysis of density, roughness, and accuracy of the atomic
diffusion additive manufacturing (ADAM) process for metal parts. Materials (Basel)
2019:12. https://doi.org/10.3390/ma1224122.
[19] Bouaziza Mohamed Ali, Djoudaab Joseph Marae, Julien Kauffmanna FH.
Microscale mechanical characterization of 17-4PH stainless steel fabricated by
Atomic Diffusion Additive Manufacturing (ADAM). Procedia Struct Integr 2020;8:
1039–46. https://doi.org/10.1016/j.prostr.2020.11.119.
[20] Kurose T, Abe Y, Santos MVA, Kanaya Y, Ishigami A, Tanaka S, et al. Inuence of
the layer directions on the properties of 316l stainless steel parts fabricated
through fused deposition of metals. Materials (Basel) 2020:13. https://doi.org/
10.3390/ma13112493.
[21] Poszvek G, Stattler G, Markl E, Seemann R, Lackner M. Fused Filament Fabrication
of metallic components for semi-professional and home use. In: Durakbasa NM,
Gençyilmaz MG, editors. Digit. Convers. W. to Ind. 4.0. Cham: Springer
International Publishing; 2021. p. 140–9.
[22] Thompson Y, Gonzalez-gutierrez J, Kukla C, Felfer P. Fused lament fabrication,
debinding and sintering as a low cost additive manufacturing method of 316L
stainless steel. Addit Manuf 2019;30:220–8. https://doi.org/10.1016/j.
addma.2019.100861.
[23] Damon J, Dietrich S. Process porosity and mechanical performance of fused
lament fabricated 316L stainless steel. Rapid Prototyp J 2019;7:1319–27. https://
doi.org/10.1108/RPJ-01-2019-0002.
[24] Gong H, Crater C, Ordonez A, Ward C, Waller M, Ginn C. Material properties and
shrinkage of 3D printing parts using ultrafuse stainless steel 316LX lament. Funct
Mater Des Dev 2018;249:1–5. https://doi.org/10.1051/matecconf/
201824901001.
Fig. 9. Stress-stain curves of sintered 3D printed samples.
M. Sadaf et al.

Journal of Manufacturing Processes 67 (2021) 141–150
150
[25] https://3dprintingindustry.com/news/desktop-metal-launches-the-studio-system-
2-3d-printer-technical-specications-and-pricing-183766/. n.d.: 183766.
[26] Safka J, Ackermann M, Machacek J, Seidl M, Vele F, Truxova V. Fabrication rocess
and basic material properties of the basf Ultrafuse 316Lx material. MM Sci J 2020;
2020:4216–22. https://doi.org/10.17973/mmsj.2020_12_2020071.
[27] Ebrahimi ND, Ju YS. Thermal conductivity of sintered copper samples prepared
using 3D printing-compatible polymer composite laments. Addit Manuf 2018;24:
479–85. https://doi.org/10.1016/j.addma.2018.10.025.
[28] Cano S, Lube T, Huber P, Gallego A, Naranjo JA, Berges C, et al. Inuence of the
inll orientation on the properties of zirconia parts produced by fused lament
fabrication. Materials (Basel) 2020:13. https://doi.org/10.3390/ma13143158.
[29] Gorjan L, Galusca C, Sami M, Sebastian T, Clemens F. Effect of stearic acid on
rheological properties and printability of ethylene vinyl acetate based feedstocks
for fused lament fabrication of alumina. Addit Manuf 2020;36:1–26. https://doi.
org/10.1016/j.addma.2020.101391.
[30] Bek M, Gonzalez-Gutierrez J, Kukla C, ˇ
Creˇ
snar KP, Maroh B, Perˇ
se LS. Rheological
behaviour of highly lled materials for injection moulding and additive
manufacturing: effect of particle material and loading. Appl Sci 2020;10:1–23.
https://doi.org/10.3390/app10227993.
[31] Venkataraman N, Rangarajan S, Matthewson MJ, Safari A, Danforth SC,
Yardimci A. Mechanical and rheological properties of feedstock material for fused
deposition of ceramics and metals (FDC and FDMet) and their relationship to
process performance. Solid Free Fabr Proc 1999:351–9.
[32] Kukla C, Gonzalez-gutierrez J, Duretek I, Schuschnigg S, Holzer C, Kukla C, et al.
Effect of particle size on the properties of highly-lled polymers for fused lament
fabrication. Am Inst Phys 2017;19:2–5.
[33] Brostow W, Buchman A, Buchman E, Olea-mejia O. Microhybrids of metal powder
incorporated in polymeric matrices: friction, mechanical behavior, and
microstructure. Polym Eng Sci 2008;48:1977–81. https://doi.org/10.1002/pen.
[34] Rang Y, Jaewoo U, Kwang K, Son J. Effect of particle size, dispersion, and
particle–matrix adhesion on W reinforced polymer composites. Res Chem Intermed
2014;40:2145–53. https://doi.org/10.1007/s11164-013-1110-7.
[35] Kukla C, Gonzalez-gutierrez J, Felfer P, Holzer C. Material extrsion with laments
for the prodction of metal parts and feedstock therefore. Met Addit Manuf 2018;4:
1–9.
[36] Agarwala MK, Van Weeren R, Bandyopadhyay A, Safari A, Danforth SC,
Priedeman WR. Filament feed materials for fused deposition processing of ceramics
and metals. Proc Ofthe Solid Free Fabr Symp 1996;7:451–8.
[37] Gonzalez-Gutierrez J, Cano S, Schuschnigg S, Kukla C, Sapkota J, Holzer C.
Additive manufacturing of metallic and ceramic components by the material
extrusion of highly-lled polymers: a review and future perspectives. Materials
(Basel) 2018:11. https://doi.org/10.3390/ma11050840.
[38] Gonzalez-Gutierrez J, Duretek I, Kukla C, Poljˇ
sak A, Bek M, Emri I, et al. Models to
predict the viscosity of metal injection molding feedstock materials as function of
their formulation. Metals (Basel) 2016:6. https://doi.org/10.3390/met6060129.
[39] Gonzlez-Gutirrez J, Beulke G, Emri I. Powder injection molding of metal and
ceramic parts. Some crit issues inject molding. 2012. p. 65–88. https://doi.org/
10.5772/38070.
[40] Md Ani S, Muchtar A, Muhamad N, Ghani JA. Binder removal via a two-stage
debinding process for ceramic injection molding parts. Ceram Int 2014;40:
2819–24. https://doi.org/10.1016/j.ceramint.2013.10.032.
[41] Kukla C, Gonzalez-gutierrez J, Felfer P, Holzer Clemens, Schuschnigg Stephan,
Cano Santiago, et al. Material extrusion with laments for the production of metal
parts and feedstock therefore. In: Metal Additive Manufacturing Conference; 2018.
[42] Banerjee S, Joens CJ. Debinding and sintering of metal injection molding (MIM)
components. Handb. met. inject. molding. 2012. p. 133–80. https://doi.org/
10.1533/9780857096234.1.133.
[43] Kong X. Powder feedstocks for micro-injection molding. Microsyst Technol 2013;8:
129–32.
[44] Krug S, Zachmann S. Inuence of sintering conditions and furnace technology on
chemical and mechanical properties of injection moulded 316L. Proc Euro Int
Powder Metall Congr Exhib Euro PM 2009;2009(2):66–70.
[45] ASM International Handbook Committee. Powder metal technologies and
applications, vol. 7; 2010.
[46] Raza MR, Ahmad F, Omar MA, German RM, Muhsan AS. Role of debinding to
control mechanical properties of powder injection molded 316L stainless steel. Adv
Mater Res 2013;699:875–82. https://doi.org/10.4028/www.scientic.net/
AMR.699.875.
[47] George E, Robert D. Deformation processing of sintered powder materials. Powder
Metall Process New Tech Anal 2012:99–138. https://doi.org/10.1179/
095066078790136454.
[48] Ren L, Zhou X, Song Z, Zhao C, Liu Q, Xue J, et al. Process parameter optimization
of extrusion-based 3D metal printing utilizing PW-LDPE-SA binder system.
Materials (Basel) 2017;10:305–29. https://doi.org/10.3390/ma10030305.
[49] V´
arez A, Levenfeld B, Torralba JM, Matula G, Dobrzanski LA. Sintering in different
atmospheres of T15 and M2 high speed steels produced by a modied metal
injection moulding process. Mater Sci Eng A 2004;366:318–24. https://doi.org/
10.1016/j.msea.2003.08.028.
[50] Pease LF, West WG. Sintering. Fundam Powder Metall 2002:220–45.
[51] ENI versalis – LDPE MV 10 r technical datasheet. 2020. p. 1–2. http://www.vers
alis.eni.com/.
[52] H¨
ogan¨
as. AM 316L Austenitic stainless steel for laser powder bed fusion. 2020.
[53] Singh KK, Sangal S, Murty GS. Hall-Petch behaviour of 316L austenitic stainless
steel at room temperature. Mater Sci Technol 2002;18:165–72. https://doi.org/
10.1179/026708301125000384.
[54] Callister Jr William D, DGR. Imperfections in solids. Mater Sci Eng Introd 2018:
92–110.
[55] Mahajan Subhash. Materials properties. Encycl Mater Sci Eng 2001:387–93.
https://doi.org/10.1179/sur.1991.7.2.117.
[56] Cano S, Gonzalez-Gutierrez J, Sapkota J, Spoerk M, Arbeiter F, Schuschnigg S, et al.
Additive manufacturing of zirconia parts by fused lament fabrication and solvent
debinding: Selection of binder formulation. Addit Manuf 2019;26:117–28. https://
doi.org/10.1016/j.addma.2019.01.001.
[57] Gibson MA, Mykulowycz NM, Shim J, Fontana R, Schmitt P, Roberts A, et al. 3D
printing metals like thermoplastics: fused lament fabrication of metallic glasses.
Mater Today 2018;21:697–702. https://doi.org/10.1016/j.mattod.2018.07.001.
[58] Khaliq H, Nobrega JM, Carneiro OS. On the use of high viscosity polymers in the
fused lament fabrication process. Rapid Prototyp J 2017;23:727–35. https://doi.
org/10.1108/RPJ-02-2016-0027.
[59] Bellehumeur C´
eline, Li Longmei, Quian Sun PG. Modeling of bond formation
between polymer laments in the fused deposition modeling process. J Manuf
Process 2004;6:170–8.
[60] Sun Q, Rizvi G. Effect of processing conditions on the bonding quality of FDM
polymer laments. Rapid Prototyp J 2008;2:72–80. https://doi.org/10.1108/
13552540810862028.
[61] Wang Z, Wei R, Ning X, Xie T, Wang J. Thermal degradation properties of LDPE
insulation for new and aged ne wires. J Therm Anal Calorim 2019;137:461–71.
https://doi.org/10.1007/s10973-018-7957-5.
[62] Aboulkas A, El har K, El Bouadili A. Thermal degradation behaviors of
polyethylene and polypropylene. Part I: pyrolysis kinetics and mechanisms. Energy
Convers Manage 2010;51:1363–9. https://doi.org/10.1016/j.
enconman.2009.12.017.
[63] Matula G, Tomiczek B, Kr´
ol M, Szatkowska A, Sotomayor ME. Application of
thermal analysis in the selection of polymer components used as a binder for metal
injection moulding of Co–Cr–Mo alloy powder. J Therm Anal Calorim 2018;134:
391–9. https://doi.org/10.1007/s10973-018-7543-x.
[64] Kang S-JL. Basis of sintering science. Sinter Densif Grain Growth Microstruct 2005:
261–5.
[65] Heaney DF. Debinding methods in metal injection molding. Handb. met. inject.
molding. 2012. p. 569–86. https://doi.org/10.1533/9780857096234.
[66] Klar E, Samal PK. Sintering and corrosion resistance. Powder Metall Stainl Steels
Process Mcrostructure Prop 2007:59–93. https://doi.org/10.1361/pmss2007p001.
[67] Suri P, Koseski RP, German RM. Microstructural evolution of injection molded gas-
and water-atomized 316L stainless steel powder during sintering (Materials
Science and Engineering A (10.1016/j.msea.2004.08.002)). Mater Sci Eng A 2005;
402:341–8. https://doi.org/10.1016/j.msea.2005.01.004.
[68] Ji CH, Loh NH, Khor KA, Tor SB. Sintering study of 316L stainless steel metal
injection molding parts using taguchi method: nal density. Mater Sci Eng A 2001;
311:74–82. https://doi.org/10.1016/S0921-5093(01)00942-X.
[69] Aan M, Subuki I. Sintering characteristics of injection moulded 316L component
using palm-based biopolymer binder. Sinter Methods Prod 2012:127–46. https://
doi.org/10.5772/32737.
[70] Frazier WE. Direct digital manufacturing of metallic components: vision and
roadmap. 21st annu int solid free fabr symp – an addit manuf conf SFF 2010 2010:
717–32.
[71] Zhong Y, Liu L, Wikman S, Cui D, Shen Z. Intragranular cellular segregation
network structure strengthening 316L stainless steel prepared by selective laser
melting. J Nucl Mater 2016;470:170–8. https://doi.org/10.1016/j.
jnucmat.2015.12.034.
[72] Ji S, Gu Q, Xia B. Porosity dependence of mechanical properties of solid materials.
J Mater Sci 2006;41:1757–68. https://doi.org/10.1007/s10853-006-2871-9.
[73] Kheiri S, Mirzadeh H, Naghizadeh M. Tailoring the microstructure and mechanical
properties of AISI 316L austenitic stainless steel via cold rolling and reversion
annealing. Mater Sci Eng A 2019;759:90–6. https://doi.org/10.1016/j.
msea.2019.05.028.
[74] Zhang Y, Feng E, Mo W, Lv Y, Ma R, Ye S, et al. On the microstructures and fatigue
behaviors of 316L stainless steel metal injection molded with gas-and water-
atomized powders. Metals (Basel) 2018:8. https://doi.org/10.3390/met8110893.
[75] R¨
ottger A, Boes J, Theisen W, Thiele M, Esen C, Edelmann A, et al. Microstructure
and mechanical properties of 316L austenitic stainless steel processed by different
SLM devices. Int J Adv Manuf Technol 2020;108:769–83. https://doi.org/
10.1007/s00170-020-05371-1.
[76] Heaney DF, Mueller TW, Davies PA. Mechanical properties of metal injection
moulded 316L stainless steel using both prealloy and master alloy techniques.
Powder Metall 2004;47:367–73. https://doi.org/10.1179/003258904225020855.
[77] Yusuf SM, Chen Y, Boardman R, Yang S, Gao N. Investigation on porosity and
microhardness of 316L stainless steel fabricated by selective laser melting. Metals
(Basel) 2017;7:1–12. https://doi.org/10.3390/met7020064.
M. Sadaf et al.