Biomedical Engineering Reference
In-Depth Information
plasma spraying offers several advantages compared to traditional
enameling, such as the high deposition speed, good control of the
substrate degradation, and minimum size tolerance, and it makes it pos-
sible to control the morphology, thickness, structure, and properties of
the coatings by tailoring the deposition parameters. Plasma spraying is a
challenging technology for the development of composite coatings. The
poor mechanical properties of bioactive glasses do not allow their use in
load-bearing devices. Their mechanical properties can be enhanced by
reinforcing themwith metallic particles (obtaining bioactive glass-matrix
composite materials, i.e. ''biocomposites''). These biocomposites could
be prepared as bulk materials as well as coatings on tough substrates.
For example, bioactive glass-matrix/Ti particle composite coatings have
been successfully deposited on Ti alloy substrates by vacuum plasma
spraying (VPS) [13]. In this case the bioactive coating provides both a
chemical bonding to the bone and a tough behavior. In order to produce
composite coatings, different methods can be used:
(a) VPS of ''composite powders,'' that is, spraying Ti particles coated
by glass, obtained by milling a sintered composite; and
(b) VPS
in situ
, that is, simply mixing glass powders and titanium par-
ticles and vacuum plasma spraying the mixture on the substrates.
Several bioactive glasses have been used as matrices for the preparation
of Ti particle-reinforced composite coatings on sand-blasted Ti-6Al-4V
substrates using the above-mentioned VPS methods. Generally, the
composite coatings obtained by VPS of the powdered pre-sintered com-
posites showed a better mechanical behavior with respect both to the
composite coatings obtained by the
in situ
method and to the pure
glass coatings. Morphological, electrochemical, and mechanical analy-
ses showed that the sintering process is a useful step for the composite
coating preparation. The best results are generally obtained by spraying
''composite powders,'' that is, powders formed by Ti particles covered
by a layer of glass obtained by milling the pre-sintered composites.
In this way the softening properties of the glass matrix are fully uti-
lized, and a better stability of the interface, both between the glass and
the dispersed particles, and between the composite coatings and the
Ti-6Al-4V substrate, can be guaranteed. However, the
in situ
method
(i.e. the deposition of mixed glass and Ti powders) is not completely sat-
isfactory in terms of homogeneity of the coating, particles distribution,
and mechanical properties.
