7.2 Composite Deposition from Particle Suspensions
243
same annealing-induced hardening is known for the particle-free electrodeposited
amorphous Ni–P matrices in which the number of steps in the thermal relaxation/crystallization depends on whether the actual sample contains more or less
phosphorous than the eutectic composition [154–157]. The advantage of the presence
of particles in such samples is that they impose a strong limitation on the crystallite
growth that renders the annealed samples nanocrystalline for a larger temperature
range than in the absence of dispersed particles.
7.2.8 Influence of the Incorporated Particles on the Wear
Damage and Friction of the Coatings
The friction coefficient and the wear damage of the composite surfaces are somewhat
interrelated properties, although their variation trends may be versatile (where “variation” is always meant in comparison with the surface of the particle-free deposit).
Due to the diversity of the origin of their change, both the increase and the decrease
in the friction coefficient may lead to diminished wear damage.
When the material of the filling particles ensures a lubrication effect upon the
scratch of the layer, both the friction coefficient of the surface and the wear damage
decreases as a result of the particle incorporation. In order to achieve this effect, the
material of the particles has to be easy to smear out along the surface. This is the
case for fluoropolymers (PTFE [75, 100, 158, 159]) and particles that exhibit layered
structure where the adhesion of the layers to each other is relatively weak (WS 2 [85,
160], MoS 2 [84, 161], graphite-type carbonaceous materials [162]). The lubricating
film formed from the sacrifice of the filling particles leads to the reduction of the
depth of the wear scratch on the deposit surface, and, additionally, the renovation
of the lubrication effect by the consumption of the composite deposits provides a
temporal stability of the low-friction state. While the friction coefficient of the metals
used in these studies (Ni, Ni–P etc.) is typically >0.8 in the absence of particles, a
much lower value can be achieved when the particles are present. Under optimal
circumstances, the friction coefficient is reduced to about 0.06–0.2 with PTFE filling
particles [75, 100, 159]. Among the layered chalcogenides, MoS 2 particles resulted
in the smallest friction coefficient of ~0.05 [161], while coating with both WS 2 and
carbon particles exhibited a friction coefficient of ~0.2 [160, 162, 163]. An effect
similar to self-lubrication was found when carbon nanotubes were codeposited with
the metal matrix [153]. Here, the friction coefficient of the composite was initially
larger than that of the pure metal; however, the order of the friction coefficient of
the pure and composite coating was inverted as the cycle number in the scratch test
increased. A friction coefficient as low as ~0.12 could be achieved with the nanotube
filling, which was the third of that of the metal matrix. This behaviour was explained
with the wear-induced re-alignment of the out-of-surface segments of the randomly
incorporated nanotubes.
243
same annealing-induced hardening is known for the particle-free electrodeposited
amorphous Ni–P matrices in which the number of steps in the thermal relaxation/crystallization depends on whether the actual sample contains more or less
phosphorous than the eutectic composition [154–157]. The advantage of the presence
of particles in such samples is that they impose a strong limitation on the crystallite
growth that renders the annealed samples nanocrystalline for a larger temperature
range than in the absence of dispersed particles.
7.2.8 Influence of the Incorporated Particles on the Wear
Damage and Friction of the Coatings
The friction coefficient and the wear damage of the composite surfaces are somewhat
interrelated properties, although their variation trends may be versatile (where “variation” is always meant in comparison with the surface of the particle-free deposit).
Due to the diversity of the origin of their change, both the increase and the decrease
in the friction coefficient may lead to diminished wear damage.
When the material of the filling particles ensures a lubrication effect upon the
scratch of the layer, both the friction coefficient of the surface and the wear damage
decreases as a result of the particle incorporation. In order to achieve this effect, the
material of the particles has to be easy to smear out along the surface. This is the
case for fluoropolymers (PTFE [75, 100, 158, 159]) and particles that exhibit layered
structure where the adhesion of the layers to each other is relatively weak (WS 2 [85,
160], MoS 2 [84, 161], graphite-type carbonaceous materials [162]). The lubricating
film formed from the sacrifice of the filling particles leads to the reduction of the
depth of the wear scratch on the deposit surface, and, additionally, the renovation
of the lubrication effect by the consumption of the composite deposits provides a
temporal stability of the low-friction state. While the friction coefficient of the metals
used in these studies (Ni, Ni–P etc.) is typically >0.8 in the absence of particles, a
much lower value can be achieved when the particles are present. Under optimal
circumstances, the friction coefficient is reduced to about 0.06–0.2 with PTFE filling
particles [75, 100, 159]. Among the layered chalcogenides, MoS 2 particles resulted
in the smallest friction coefficient of ~0.05 [161], while coating with both WS 2 and
carbon particles exhibited a friction coefficient of ~0.2 [160, 162, 163]. An effect
similar to self-lubrication was found when carbon nanotubes were codeposited with
the metal matrix [153]. Here, the friction coefficient of the composite was initially
larger than that of the pure metal; however, the order of the friction coefficient of
the pure and composite coating was inverted as the cycle number in the scratch test
increased. A friction coefficient as low as ~0.12 could be achieved with the nanotube
filling, which was the third of that of the metal matrix. This behaviour was explained
with the wear-induced re-alignment of the out-of-surface segments of the randomly
incorporated nanotubes.