7.2 Composite Deposition from Particle Suspensions
241
planes [82, 127]. Nevertheless, the preferred incorporation site of the nanoparticles
is also a boundary between the crystals of the metal matrix.
The incorporation ratio of nanoparticles as rated by their weight (or volume) per
cent often shows smaller values than that of microparticles (with otherwise identical
deposition conditions, including the weight-based concentration of the particles in
the solution) [103, 121]. However, if we scrutinize the numerical density of the
incorporated particles, nanosized particles are much more abundant in the composite
deposits, which leads to greater effect on the structure. Electroplated composites with
nanoparticles are also associated with better dispersion and lower surface roughness
than those obtained with microparticles.
The experience is that nearly all deposit properties investigated for composites
improve when nanoparticles used for plating instead of microparticles. These features
can be the microhardness [102, 124, 126], friction coefficient [102, 125] and resistance to either wear/abrasion [102, 103, 108, 122, 125], corrosion [103–105, 124,
125] or oxidation [120].
7.2.7 Grain Size and Hardness of Granular Coatings
Electrodeposited composites are often discussed rather with respect to their properties
and functionality than their composition. The main reason for this type of treatment
is that the beneficial impact of the inert particles present in a metal matrix largely
stems from the structural change in the metal matrix caused by the particles instead
of their chemical nature. Therefore, it is not surprising that very similar trends can
be obtained for a large variety concerning the chemical nature of either the metal
matrix or the particles.
The major cause of the change in the mechanical properties of the dispersion
coating as compared to their purely metallic counterparts is the grain refinement.
This is merely an effect of the disturbance of the crystal growth by the particles being
present. A representative image on the grain structure of pure metallic and particleloaded deposits can be seen in Fig. 7.6. As mentioned above, this is unrelated to
the composition of the particles; moreover, even the shape of the particles is of no
matter. Although the spherical particles are typical in the nanoparticle codeposition
studies, essentially the same grain refinement can be achieved with nanorods [128,
129] and nanotubes [90].
The hardness change due to the presence of particles in a metal is called dispersion
hardening. The presence of particles modifies the deformation mechanism of the
metal grains by limiting the dislocation movement distance. This leads to the situation
that, together with the grain refinement, MMCs are harder than the matrix metal itself.
Grain refinement-related mechanical improvement can be equally observed for
hard ceramic particles (like diamond [131, 132], Al 2 O 3 [77, 133–135], AlN [136],
Cr 2 O 3 [96], CeO 2 [128, 137–139], SiC [124, 129, 140–142], Si 3 N 4 [101], SiO 2
[102], TiO 2 [143, 144], TiB 2 [145]) and also for metal particles (Al [130], Cr [146]
and Ti [83]). Even soft particles can lead to hardening when their concentration in
241
planes [82, 127]. Nevertheless, the preferred incorporation site of the nanoparticles
is also a boundary between the crystals of the metal matrix.
The incorporation ratio of nanoparticles as rated by their weight (or volume) per
cent often shows smaller values than that of microparticles (with otherwise identical
deposition conditions, including the weight-based concentration of the particles in
the solution) [103, 121]. However, if we scrutinize the numerical density of the
incorporated particles, nanosized particles are much more abundant in the composite
deposits, which leads to greater effect on the structure. Electroplated composites with
nanoparticles are also associated with better dispersion and lower surface roughness
than those obtained with microparticles.
The experience is that nearly all deposit properties investigated for composites
improve when nanoparticles used for plating instead of microparticles. These features
can be the microhardness [102, 124, 126], friction coefficient [102, 125] and resistance to either wear/abrasion [102, 103, 108, 122, 125], corrosion [103–105, 124,
125] or oxidation [120].
7.2.7 Grain Size and Hardness of Granular Coatings
Electrodeposited composites are often discussed rather with respect to their properties
and functionality than their composition. The main reason for this type of treatment
is that the beneficial impact of the inert particles present in a metal matrix largely
stems from the structural change in the metal matrix caused by the particles instead
of their chemical nature. Therefore, it is not surprising that very similar trends can
be obtained for a large variety concerning the chemical nature of either the metal
matrix or the particles.
The major cause of the change in the mechanical properties of the dispersion
coating as compared to their purely metallic counterparts is the grain refinement.
This is merely an effect of the disturbance of the crystal growth by the particles being
present. A representative image on the grain structure of pure metallic and particleloaded deposits can be seen in Fig. 7.6. As mentioned above, this is unrelated to
the composition of the particles; moreover, even the shape of the particles is of no
matter. Although the spherical particles are typical in the nanoparticle codeposition
studies, essentially the same grain refinement can be achieved with nanorods [128,
129] and nanotubes [90].
The hardness change due to the presence of particles in a metal is called dispersion
hardening. The presence of particles modifies the deformation mechanism of the
metal grains by limiting the dislocation movement distance. This leads to the situation
that, together with the grain refinement, MMCs are harder than the matrix metal itself.
Grain refinement-related mechanical improvement can be equally observed for
hard ceramic particles (like diamond [131, 132], Al 2 O 3 [77, 133–135], AlN [136],
Cr 2 O 3 [96], CeO 2 [128, 137–139], SiC [124, 129, 140–142], Si 3 N 4 [101], SiO 2
[102], TiO 2 [143, 144], TiB 2 [145]) and also for metal particles (Al [130], Cr [146]
and Ti [83]). Even soft particles can lead to hardening when their concentration in