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Materials Science in Additive Manufacturing Directed energy deposition

critical. Surface technologies can dramatically increase the Broad-beam laser-DED (B-DED) is another highly
longevity of cast iron components and lower replacement effective deposition technique that uses a rectangular laser
costs. These technologies include spraying, deposition, spot and matching rectangular powder nozzle to cover a
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vapor deposition, and, notably, laser-directed energy larger area in a single pass. It has been reported that
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deposition (DED). 6,7 the B-DED process can successfully deposit coatings
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Austenitic stainless steel is widely used in aerospace, with a thickness exceeding 1 mm. Sun et al. used this
automotive, marine, and biomedical applications due to system to prepare FeBSiNb coatings and analyzed their
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its excellent mechanical properties, toughness, and low forming quality and wear resistance. Lei et al. employed
cost. 8-11 Zeng et al. evaluated candidate metallic materials the B-DED process, utilizing a laser internal powder
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feeding nozzle to produce single-track multi-layer walls.
for typical combustion systems and concluded that Although previous work has evaluated the feasibility of
austenitic stainless steel might be essential for future flue gas
systems. However, the low hardness of austenitic stainless high-efficiency deposition with B-DED, its performance,
steels and their susceptibility to wear and scratching limit mainly wear resistance, has yet to be widely studied. Thus,
before considering replacing conventional DED methods
their application. Zhu et al. investigated the tribological in cast iron applications, a thorough investigation of
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properties of 316L SS under lubricated conditions. They thick coatings produced by H-DED and B-DED must be
found that the frictional resistance of these parts was carried out.
lower than that of parts manufactured using conventional
methods. Current research on austenitic stainless steels has At present, the main focus of research on DED cast
focused on the wear resistance and durability of austenitic iron is examining the mechanical characteristics of
stainless steels prepared by conventional casting and coatings made with various deposition materials and
additive manufacturing techniques, with less research on process variables. Studies examining the differences in
the wear resistance of austenitic stainless steels prepared by microstructure and characteristics between coatings made
the DED process and its derivatives. Understanding these with various kinds of lasers are, nevertheless, limited. In
differences is critical to selecting the proper process for a this investigation, double-layer austenitic stainless-steel
specific application in harsh environments. coatings were deposited to a surface of ductile cast iron
using H-DED and B-DED procedures. The microstructure
With advancements in productivity, traditional circular and wear resistance of the two types of coatings were
spot DED has struggled to meet the increasing industrial characterized to explore their potential mechanisms.
demands, in terms of deposition efficiency, making it crucial
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to explore more efficient technologies. Higher deposition 2. Materials and methods
speeds and improved performance are possible with high-
speed DED (H-DED), which combines the benefits of 2.1. Materials
different surface coatings. Different from conventional The deposition substrate used in this study is commercially
DED, the powder convergence location in H-DED is above available ductile cast iron QT500-7, whose microstructure
the substrate. Therefore, the H-DED coating significantly consists of ferrite and pearlite, with some pearlite forming
reduces the heat input to the substrate. This change in the a unique spheroidal graphite structure. The shape of the
forming principle enhances the deposition efficiency and deposition powder (Chengdu Huayin Powder Technology
powder utilization and reduces the heat-affected zone of Co., Ltd., China) is depicted in Figure 1. It is an austenitic
H-DED. 15,16 The microstructure and characteristics of stainless steel powder with an average particle size of 35 –
Ni-based coatings made by H-DED and conventional 50 μm. It was created using the gas atomization process.
DED were compared by Yuan et al. They found that Table 1 presents the nominal chemical composition of the
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the H-DED layer had less roughness but was smaller in powder and substrate.
thickness; its resistance to wear and corrosion increased
with deposition speed. Zhang et al. found that H-DED 2.2. Coating preparation
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coatings have advantages such as lower dilution rates and A KUKA robotic arm was used to hold the RFL-C4000
better mechanical properties compared to traditional high-power fiber laser (rated at 4 kW) to achieve coaxial
DED. H-DED has overcome the efficiency bottleneck H-DED. The powder feeder used was the DPSF-2 model
of the traditional DED process, enabling the successful (with a powder feeding precision of ≤±2% and a rated
production of high-quality coatings with strong bonding powder feeding rate of 6 rad/min). The B-DED system
strength. However, the application of coatings with a included a 6-kW fiber laser (YLS-KC 6000; IPG Photonics,
thickness exceeding 1000 μm faces significant challenges United States of America [USA]) and an Infi-pro dual-
due to the need for carefully designed deposition nozzles. cylinder coaxial powder feeder (United Technologies

Volume 3 Issue 4 (2024) 2 doi: 10.36922/msam.4974