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Materials Science in Additive Manufacturing AM-produced CoCrFeMnNi properties

materials generally fail in a brittle manner, which occurs processing methods. In recent years, corrosion resistance of
rapidly almost with no plastic deformation , which CoCrFeMnNi HEA was investigated for samples produced
[21]
should be avoided to prevent catastrophic failures. Kim by conventional methods [30-33] , DED and SLM [35-38] . Xu
[34]
[38]
[22]
et al. used vacuum induction method (VIM) to et al. compared the corrosion properties of SLMed
fabricate CoCrFeMnNi HEA and showed that its absorbed and as-cast CoCrFeMnNi and found that the former
energy was significantly higher than that of many other exhibit better corrosion resistance due to homogeneity
alloys. A similar study was performed by Xia et al. who of components and grain refinements. It was found that
[23]
used vacuum levitation melting to produce CoCrFeNi the corrosion resistance of HEA thin film in sea water
HEA with varying amount of Al addition. It was observed benefits form heat treatment . However, studies on bulk
[33]
that addition of Al lowered the impact energies at room SLMed HEAs of Al CoCrFeMnNi showed that corrosion
x
[39]
temperature, and at Al concentrations close to that of Mn resistance declines after heat treatment . Xiang et al.
[35]
in CoCrFeMnNi, toughness dropped from 287.44 J to 1.28 showed that corrosion resistance of SLMed Ti-6Al-4V is
J compared to pure CoCrFeNi. Bi et al. investigated dependent upon the laser power and laser scanning speed.
[24]
impact toughness of CoCrFeMnNi produced by laser DED. However, the trend in relationship between a process
The impact toughness at 0°C was found to be four time parameter and corrosion resistance was not linear, for
smaller compared to the same alloy made by VIM. Kim example, it increased with scan speed up to certain value
et al. obtained excellent impact toughness performance after which higher scan speeds caused lower corrosion
[25]
at cryogenic temperatures for CoCrFeMnNi produced performance while the linear increase of laser power led to
by SLM, and they attributed the high performance to the oscillating behavior of the resistance.
formation of many deformation twins. The critical literature analysis indicates that although
In general, the as-built alloy components from SLM CoCrFeMnNi is one of the most studied HEAs, the majority
processes need to receive some form of heat treatment of published works focus on such materials obtained
for stress relieving and other purposes. Little information by the conventional processes, such as casting and thin
is available regarding heat treatment of additively film deposition. For the existing works on CoCrFeMnNi
manufactured CoCrFeMnNi HEA in the literature, obtained by AM processes, most investigated the as-built
and thus, the limited existing research on heat treating materials, but the effects of heat treatment on properties,
CoCrFeMnNi fabricated from other manufacturing such as impact fracture and corrosion resistance, remain
processes is summarized in the following. Vaidiya et al. uncharted. In reality, heat treatment is critical for metal
[26]
showed that single FCC phases in arc melted CoCrFeNi and AM in that it provides the stress relief and homogenization
CoCrFEMnNi could be retained after thermal exposure for metal alloys after the highly non-equilibrium melting
at least up to 1373 K for an extended period of time, and and solidification in the laser AM processes. To bridge the
the thermal exposure caused no disturbance to elemental gap, the current work investigates CoCrFeMnNi obtained
[27]
distribution. In another study of the same group , a Cr C from the dominant metal AM process, SLM, with a focus on
3
7
contamination was found whose phase fraction did not the comparison of microstructure and properties between
change significantly with temperature, suggesting little the as-built and heat-treated materials. It is expected
dissolution of this phase during the thermal exposure up to that the findings can shed light on the understanding of
[28]
1373 K. Laplanche et al. studied inductively melted and CoCrFeMnNi HEA obtained from the complete SLM
casted CoCrFeMnNi that was annealed at 870 – 1270 K process, followed by heat treatment.
for 1 h. Slight increase in hardness was found in materials 2. Materials and methods
annealed at lower temperature, which dropped rapidly due
to the onset of recrystallization and grain growth. Sathiaraj 2.1. SLM experiments
et al. investigated how heating rate affects microstructure Spherically shaped pre-alloyed particles of equiatomic
[29]
evolution of heavily cold-rolled CoCrFeMnNi HEA. The CoCrFeMnNi, made by gas atomization, were acquired
studied temperature range was between 700°C and 1000°C for this study. The particle size distribution ranged from 15
using high (10°C/s) and low (~0.13°C/s) heating rates. It to 53 μm, with an average diameter of 30 μm. A Concept
was found that heating rate significantly affected grain size Laser Mlab machine was adopted for SLM fabrication of
and grain distribution; low rates led to larger grains with HEA samples. In the SLM operation, argon was filled in
wider size distribution, which is a consequence of early the build chamber to avoid oxidation, and the substrate
activation of potential nucleation sites.
material is a stainless steel plate. There are two stages of
How a given HEA reacts in a corrosion environment SLM experiments. In the first stage, the appropriate SLM
depends on its microstructure, alloying elements, and process condition for CoCrFeMnNi on the particular

Volume 2 Issue 1 (2023) 3 https://doi.org/10.36922/msam.42