Page 62 - MSAM-1-2

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

additives [25-27] . For example, Koivuluoto et al. successfully With both dendritic and spherical copper particles,
deposited copper + alumina coatings onto a substrate via the Vickers hardness for all the coatings obtained with
cold spray process. Dendritic and spherical copper powders spherical copper powders is higher (ranging between 106
were mixed with 10 vol.%, 30 vol.%, and 50 vol.% of alumina. Hv and 127 Hv) when compared to the coatings obtained
Then, its cold spraying characteristics were compared with with dendritic copper particles (ranging 83 – 103 Hv).
that of the pure copper coatings made with dendritic and The corrosion resistance of these coatings made with
spherical copper powders. The thickness of the copper- spherical copper powders + alumina was higher than the
alumina coatings increased with the increasing amount of dendritic copper powder coatings. The spherical copper +
alumina ceramic particles, mainly due to the hammering alumina powder coatings were denser, as reported in the
effect of alumina particles on the ductile copper matrix. literature .
[28]
The shot peening effect of the ceramic particles deforms the [29]
copper powders; thus, porosity decreases, which enhances In another work, Phani et al. successfully cold-
the bonding characteristics. According to Koivuluoto et al., sprayed nanocrystalline copper-alumina powders and
the densest coatings obtained were for dendritic copper + studied the effect of heat treatments at the temperatures
50 vol.% alumina and 10 vol.% alumina + spherical copper. of 300°C, 600°C, and 950°C, and inferred that alumina
Figures 5-8 show the field emission scanning electron particles were effective in stopping the grain growth,
microscopy (SEM) micrographs of these coatings. The which is of immense value for commercial applications.
reason for this, as reported, was that the dendritic copper Figure 9 shows the micrographs of the as-sprayed and
particles have a higher surface area and are more prone to heat-treated coatings. The variation in the grain size due
oxidation as compared to the spherical copper powders. to the heat treatments, as reported, was significantly less
Eventually, these dendritic copper powders require more for copper-alumina coatings compared to pure copper
deformation to achieve better metal-metal bonding and coatings. The same trend was detected for microhardness,
an effective dense coating. However, the Vickers hardness where nanocrystalline copper-alumina coatings had
of copper + alumina coatings showed a constant rise with higher hardness than the pure copper coatings for all heat
the increase in alumina particles for the coatings obtained. treatment temperatures. As reported, the copper-alumina

A B A B

Figure 5. Field emission scanning electron microscopy micrographs of Figure 7. Field emission scanning electron microscopy micrographs of
(A) dendritic copper + 10 vol.% Al O and (B) dendritic copper + 30 (A) spherical copper + 10 vol.% Al O coatings on steel substrate and its
2
3
2
3
[28]
vol.% coatings on steel substrate . (Reprinted from Journal of Thermal (B) detailed microstructure . (Reprinted from Journal of Thermal Spray
[28]
Spray Technology, 19(5), Koivuluoto, H., and Vuoristo, P., Effect of Powder Technology, 19(5), Koivuluoto, H., and Vuoristo, P., Effect of Powder Type
Type and Composition on Structure and Mechanical Properties of Cu + and Composition on Structure and Mechanical Properties of Cu + Al O 3
2
Al O Coatings Prepared using Low-Pressure Cold Spray Process, 1081 – Coatings Prepared using Low-Pressure Cold Spray Process, 1081 – 1092,
2
3
1092, 2010, with permission from Springer Nature). 2010, with permission from Springer Nature).
A B A B

Figure 6. Field emission scanning electron microscopy micrographs of Figure 8. Field emission scanning electron microscopy micrographs of
(A) dendritic copper + 50 vol.% Al O coatings on steel substrate and its (a) spherical copper + 30 vol.% Al O and (B) spherical copper + 50 vol.%
3
2
3
2
(B) detailed microstructure . (Reprinted from Journal of Thermal Spray coatings on steel substrate . (Reprinted from Journal of Thermal Spray
[28]
[28]
Technology, 19(5), Koivuluoto, H., and Vuoristo, P., Effect of Powder Type Technology, 19(5), Koivuluoto, H., and Vuoristo, P., Effect of Powder Type
and Composition on Structure and Mechanical Properties of Cu + Al O 3 and Composition on Structure and Mechanical Properties of Cu + Al O 3
2
2
Coatings Prepared using Low-Pressure Cold Spray Process, 1081 – 1092, Coatings Prepared using Low-Pressure Cold Spray Process, 1081 – 1092,
2010, with permission from Springer Nature). 2010, with permission from Springer Nature).
Volume 1 Issue 2 (2022) 6 https://doi.org/10.18063/msam.v1i2.12