Page 63 - MSAM-1-2

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

A B in electrical conductivity of copper-alumina coatings
was very less after the salt spray test and Kesternich test.
Electrical conductivity values of 51% IACS and 58% IACS
were measured for copper-alumina coatings after salt
spray and Kesternich tests, respectively. According to the
analysis, there were layers of Cu Cl(OH) (paracetamite),
3
2
which might also enhance corrosion resistance .
[30]
C D Chen et al. prepared copper-alumina-graphite cold-
[31]
sprayed coatings (for lubrication purposes) with 304
stainless steel plates as substrates. The feedstock powders
prepared were pure copper, copper-alumina (10 wt.%), and
copper-alumina (10 wt.%)-copper-coated graphite (5 wt.%,
10 wt.%, and 20 wt.%) powders. As reported, the pure
copper coatings had around 365 µm thickness along with
Figure 9. Microstructure of (A) copper coating (as-sprayed), (B) copper small pores. However, with the incorporation of 10 wt.%
coating heat treated at 950°C, (C) copper-alumina coating (as sprayed), alumina, the number of pores was significantly reduced,
and (D) copper-alumina coating heat treated at 950°C . (Reprinted possibly due to the hammering effect of alumina ceramic
[29]
from Acta Materialia, 55, Sudharshan Phani, P., Vishnukanthan, V., and particles. The thickness of the coating also drastically
Sundararajan, G., Effect of heat treatment on properties of cold-sprayed improved to 859 µm. However, with the addition of
nanocrystalline copper-alumina coatings, 4741 – 4751, 2007, with
permission from Elsevier). copper-coated graphite, the thickness of coatings was
reduced to 480, 400, and 562 µm for copper-alumina
coatings showed only a 9% reduction in hardness post- (10 wt.%)-copper-coated graphite (5 wt.%, 10 wt.%, and
heat treatment at 950°C, whereas the pure cold-sprayed 20 wt.%) cold-sprayed coatings, respectively. Figure 10
copper showed a 55% decrease in hardness, which gives shows SEM micrographs of Cu-based solid lubricating
nanocrystalline copper-alumina coatings an edge over cold spray coatings.
coarse-grained copper coatings. The electrical conductivity As reported, among the hardness values of copper-
of nanocrystalline copper-alumina coatings was reported based coatings, copper-alumina coatings had the highest
to be around 20 – 25 MS/m, which is lesser than the Brinell hardness of 114.3 as compared to the pure copper
conductivity of nanocrystalline copper coatings which coating with a Brinell hardness of 97.0 as well as with
had a reported value of around 50 MS/m. This electrical copper-alumina-copper-coated graphite coatings ranging
conductivity behavior of the coatings could be attributed around 107.3 – 88.2. There was a decrease in hardness with
to the presence of alumina ceramic particles . the increasing amount of copper-coated graphite in the
[29]
In addition to the studies above, Winnicki et al. copper-based LPCS solid lubricant coatings. The lamellas
[30]
studied the corrosion resistance of copper-alumina cold of copper in the copper-alumina-copper-coated graphite
spray coatings with cyclic salt spray and Kesternich tests. 5 wt.% are large with less plastic deformation. However,
As reported, even after 18 cycles of NaCl sprays on copper- with the increase in copper-coated graphite content from
alumina coatings, there was no significant corrosion, 5 wt.% to 10 wt.% and further to 20 wt.%, the relative
possibly because of the low amount of ceramic particles plastic deformation increased, which could be mainly due
in the Cu + Al O coating accounting to lesser weak metal to the hammering effect and the relatively higher amount
2
3
ceramic interfaces allowing the chloride ions to penetrate of alumina in copper-alumina (10 wt.%)-copper-coated
[31]
in them, so there was no buckling in the coatings. However, graphite (10 wt.% and 20 wt.%) .
for the Kesternich test performed in sulfur dioxide Dry sliding wear performance of copper-based solid
environment, there were some small cracks at the boundary lubrication coatings was also studied by Chen et al. ;
[31]
between the substrate and the coatings. Furthermore, the they found that the pure copper coatings had a friction
electrical conductivity test performed on copper-alumina coefficient of 0.82 and the copper-alumina coatings had
coatings also did not show a huge difference in electrical a friction coefficient of 0.94. With the incorporation
conductivity between as-sprayed copper-alumina coatings of copper-coated graphite, the friction coefficient
and the copper-alumina coatings after the two corrosion was reduced due to the increase in solid lubrication.
tests (salt spray and Kesternich tests). The electrical The reported values of friction coefficients were 0.69,
conductivity reported for as-sprayed copper-alumina 0.29, and 0.34 for copper-alumina (10 wt.%)-copper-
coating was 62% IACS. However, interestingly, the drop coated graphite (5 wt.%, 10 wt.%, and 20 wt.%) cold-

Volume 1 Issue 2 (2022) 7 https://doi.org/10.18063/msam.v1i2.12