Page 16 - MSAM-2-3

Materials Science in Additive Manufacturing High-performance materials in AM

G=H−TS (I) fabrication of bulk HEAs using AM technology , the
[98]
where H is the enthalpy, T is the absolute temperature, influence of process parameters such as scanning speed
and S is the entropy. and laser power on the final microstructure of the finished
product has been investigated in both the PBF and DED
Compared to conventional alloys, HEAs have several techniques [99,100] . Further attempts have been made to
outstanding core effects such as diffusion hysteresis effect optimize the temperature gradients and cooling rates
and cocktail effect. These effects associated with solid during material fabrication by means of improved scanning
solution strengthening can lead to a variety of unique strategies or the use of ultrasonic assistanc .
[99]
properties, including microstructural stability and
oxidation resistance. Different studies have been carried For another frequently used alloy system in research,
out to investigate the mechanical, electrical, and other AlxCoCrFeNi, a new study published is equally
[98,101]
properties of HEAs , and new HEAs are also constantly exciting . This study, using the LPBF technique,
[90]
developed for use in a variety of applications and in special succeeded in preparing a high-strength alloy with a
layered microstructure consisting of body-centered cubic
advanced fields . HEAs can also be used as metallic and face-centered cubic nanospheres layer by layer from
[91]
materials under extremely high or low temperature
operating conditions. AlCoCrFeNi alloys, making it stronger and more ductile
than other alloys [101] .
In their application as refractory materials, HEAs can
maintain structural stability at high temperatures due In addition, two popular research directions in the
to lattice distortion, high entropy effects, and diffusion field of HEAs processing by AM technology are in situ
alloying and in situ strengthening. In situ alloying is the
hysteresis [92,93] . Since 2010, few research groups have direct in situ synthesis of HEAs by AM technology without
successfully produced NbMoTaW and VNbMoTaW that pre-alloying. Through such studies, it has been found that
can withstand temperatures of up to 1600°C [92,94] . Since then, the AM technique allows the costly pre-alloying process
through the incessant innovations and breakthroughs made
by the researchers, the practical value of HEAs in the field to be bypassed in favor of the direct preparation of HEAs
of refractory materials has been increased by reducing their from different pure metal powders, with acceptable
densities and excellent mechanical properties
. In situ
[102]
density and improving many of their properties, including strengthening, on the other hand, refers to the generation
ductility [93,95,96] . In the field of cryogenic applications, of strengthening particles directly in the process through
research into HEAs has also yielded impressive results. in situ chemical reactions between different elements
A recent study on CrCoNi-based medium- and high- or compounds during processing. In this way, a more
entropy alloys demonstrated that CrCoNi with excellent homogeneous and detailed particle distribution, which
damage tolerance exhibits high fracture toughness at is indicative of a better strengthening performance, can
temperatures as low as 20 K and shows a deformation be obtained, as compared with the particle distribution
structure different from that at higher temperatures .
[97]
obtained with conventional methods [103,104] . The emergence
This unique property is due to the synergistic effect of these two research directions means that both AM
of multiple microstructures such as dislocation slip and technology and HEAs materials are refining each other,
twin structure, and the performance of HEAs beyond that which is beneficial to devising a manufacturing method
of other conventional materials once again demonstrates of greater value.
the extraordinary potential of HEAs for future high-
performance alloys . 4.3. Processing of high entropy alloys composites
[97]
and future directions
4.2. Integration with additive manufacturing
The HEA composites can be prepared by two methods:
As HEAs are promising materials in many applications, (i) The addition of other substances to the HEAs matrix
studies have been conducted to investigate their processing to form metal matrix composites, and (ii) the addition
by AM technology. As a metallic material, the suitability of HEAs particles to a conventional alloy matrix to form
of HEAs as a raw material for AM technology has been metal-metal composites [105,106] . Both of these categories
relatively well studied, and subsequent research has begun have been studied specifically for manufacturing with the
to investigate the effect of the different parameters applied application of AM technology, and it has been verified that
in the processing by different AM technologies on the the composites possess, for example, improved tensile and
performance of the final product. friction resistance properties [107] .
In the case of the CoCrFeNi alloy system, for example, In the future, as more unique properties of HEAs
which is the most frequently used system to study the are explored and exploited, the synergy between HEAs

Volume 2 Issue 3 (2023) 10 https://doi.org/10.36922/msam.1587