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Materials Science in Additive Manufacturing Cold spray additive manufacturing of Cu-based materials

of the equiaxed grains visible in this region. However, in
Region B, only the breaking up of elongated subgrains
was visible, suggesting that the temperature increase was
not too high as compared to the region A. Furthermore,
in Region D, only dislocation cells were seen and not the
subgrains, which shows that the temperature rise was even
lesser as compared to the Region B as well as A.
Borchers et al. also measured the resistivity of the
[24]
copper coatings, which was identified to have values
close to the resistivity of cold-rolled copper sheets. In
their work, they suggested that the cold-sprayed coatings
can acquire better electrical properties when compared
to high-velocity oxygen fuel (HVOF)-fabricated copper
coatings. The copper coatings produced by cold spray were
very dense, consisting of good metallic bonding between
Figure 4. A particle-particle triple point of cold-sprayed copper coating the particles. Most importantly, the oxide formation was
is seen in this TEM micrograph . (Reprinted from Materials Research
[24]
Society Symposium – Proceedings, 674, Borchers, C., Stoltenhoff, T., negligible in cold-sprayed copper coatings. However, the
Gärtner, F., Kreye, H. and Assadi, H., Deformation microstructure of cold bond strength of HVOF copper coatings is higher than the
gas sprayed coatings, P7.10.1-P.10.6, 2001, with permission from Springer bond strength of copper cold spray coatings.
Nature).
3. Copper-based metal matrix composite
high dislocation density having dislocation arrangement in cold spray coatings
walls. The marked Region “B” displays aligned elongation The metal matrix composite coatings with copper as the
of grains with high dislocation density. Then, Region “A” base metal are of great commercial importance. Copper-
reveals the ultrafine grains with high dislocation density, based MMC coatings can be utilized in power industries,
specifically at the grain boundaries. Finally, Region “C” especially in the manufacturing of seam welding electrodes,
shows dislocation-free regions having deformation twins. electrical contacts, lead wires, and conductors for high-
The direction of flight of the particles has been marked on temperature electrical applications. These coatings can
the micrograph along with three other directions showing be produced through techniques such as HVOF and
the particle-particle interface.
CGDS. The oxide formations and phase transformations
Basically, particles can be seen making a triple point. in the HVOF coatings degrade the properties of the
Between Regions B and D, the particle-particle interface coatings. The CGDS process is currently being utilized
is 70°, and between Regions A and C, the particle-particle in fabricating various copper-based MMC coatings.
interface is 45°. As seen in the micrograph, there are Several reinforcements such as SiC, CNT, AlN, graphene,
particles impacting at different angles, according to which alumina, MoS , WC, and TiB have been employed to
2
2
the local temperatures may also be different. This may make successful cold spray coatings. Each reinforcement
give rise to the process of recrystallization, which can has characteristic properties; thus, they are selected
account for microstructural changes as compared to the accordingly to impart the same worthy properties in the
initial powder feedstock. As discussed by Borchers et al. , copper metal matrix composite coatings. Several research
[24]
Region C consisted of twins. This could be due to the high projects have already been done in this area, proving the
strain rate deformation and subsequent recrystallization worth of such composite coatings, which are reviewed in
during annealing caused by local temperature increase. the next section.
Due to the extremely short cooling time of around 10
-4
s, the fraction of coating that has recrystallized is very 4. Recent investigations into copper-based
less. As far as the deformation in Regions A, B, and D is MMC coatings
concerned, there could be several steps into which the
whole recrystallization process can be divided; first, the 4.1. Copper-alumina cermet coatings
formation of randomly distributed dislocations; second, Several studies have been done on copper as a metallic
the development of long dislocation cells due to dynamic matrix with ceramic reinforcement (also known as
recovery; and third, the elongated subgrains form, followed cermets). Recently, special attention has been given to
by the breaking up and formation of small equiaxed grains. ameliorating mechanical properties and wear resistance
In Region A, the rise in temperature is the highest because of various copper-based coatings using hard particles as

Volume 1 Issue 2 (2022) 5 https://doi.org/10.18063/msam.v1i2.12