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Bioceramic coating of hydroxyapatite on titanium
substrate with Nd-YAG laser
Reference: Materials Science and Engineering: C, Volume 25, Issue 4, June 2005, Pages 541-547 Gary J. Cheng,
Daniel Pirzada, M. Cai, Pravansu Mohanty, Amit Bandyopadhyay
Instructor: T.Y.Kuo
Student: W.D.Dai
Date: 9.28.2012
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Outline
 Introduction
 Experimental method
 Coating Schemes
 Conclusions
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Introduction
Hydroxyapatite (HA):
 Compatible with various tissue types
 Outstanding osteoconductivity
 Since titanium has poor osteoinductive properties, the concept of applying
HA onto metallic implants as a surface coating was developed
 Although HA has good mechanical properties and osteoinductive.but
brittleness, low tensile strength, and poor impact resistance.
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Experimental method(1/2)
 In Fig.1 its shows HA very low absorption
to Nd-YAG laser-stay at low temperature.
 Most laser power is transmitted and scattered
by HA until its finally absorbed by Ti powder
and the substrate.
 HA powders are kept in low temperature before
the powders are entrapped into metallic layer and
form a strong bonding with the metallic substrate.
Fig. 1. Spectrum of HAp at UV-Near
range
Infrared
 The absorption of metal to laser is the highest in
infrared range, while HA is transparent to infrared
light but opaque to UV light.
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Experimental method(2/2)
 Thin plate of Titanium (10mm) is spray-coated with mixture of the precursor
and organic solvent (acetone)
 After drying use Nd:YAG coating HA on substrate.
 After coating,use SEM the coating is analyzed by EDS attached to the SEM.
 The measurement of hardness and modulus by nanoindentation
 The determination of the interfacial toughness of this HA/Ti substrate system
by Vickers indentation
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Coating Schemes(1/6)
 Since HA does not absorb laser,
HA powders will stay at low
temperature before they are
entrapped into metallic layer
 Result in 3 layers: porous
Fig. 2. Schematic representation of monolayer HAp ceramic coating on
Ti substrates. (a)Laser coating of HAp powders. (b) Composite
microstructure Monolayer porous coating after laser coating.
HA layer, dense HA/Ti bonded
structure layer and Ti substrate.(Fig.2)
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Coating Schemes(2/6)
 The top layer is a less dense HA coating. The
less dense and porous HA layer is preferred for cell
growth by forming a strong bonding between HA and
body cell
 The mid-layer is a composite
structure where HA powders
are entrapped in Ti molten zone.
 The density of HA decreases
with the depth increasing.
Fig. 3. Cross-sectional SEM micrograph of HAp coated Ti6a14V substrate using an
Nd:YAG laser with power of 100W and scanning velocity of 1 mm/s
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Coating Schemes(3/6)
 In Fig. 4(a) that HA powders are
entrapped in Ti molten zone forming
a composite structure with a solid
HA/Ti bonding.
 Fig.4(b) shows another area
Fig. 4. The SEM micrograph and chemical analysis by EDS on the
cross-section of coating (a) HAp/Ti composites at interface
with a further depth from the
surface than Fig. 4(a)
 HA/Ti composite structures were
also found in Fig. 4(b), however
the density of HA is less than
that in Fig. 4(a)
(b) HAp/Ti composites with depth increasing
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Coating Schemes(4/6)
 The substrate layer of Ti,
is shown in Fig. 4(c)
 The elastic modulus from
nanoindentation test
(c) Titanium substrate
 From Fig. 5 that porous HA
coatings near the top surface has
low elastic modulus. The elastic
modulus increases gradually
Fig. 5. The elastic constant results of the HAp coating on Titanium
substrate from nanoindentation test.
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Coating Schemes(5/6)
 Hardness test
Fig. 6(a) shows the hardness of
many points on the coating surface.
Near the top surface, porous HA
coatings has low hardness. The
hardness is highest right below
Fig. 6. The hardness results of the HAp coating on Titanium substrate from
the porous coatings. the highest
nanoindentation test. (a) Hardness distribution near the coating surface.
hardness (7¨9GPa)
 Fig. 6(b) It shows that the hardness
of HA/Ti interface decrease
continuously to 2.5¨3GPa a
(b)Hardness from nanoindentation at a larger depth scale.
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Coating Schemes(6/6)
 Fig. 7 There is no apparent crack
on the edges and corners of the
indent. This is because the ductility
of the coating is enhanced by the
HA/Ti composite structure.
Fig. 7. Image of indentation after microhardness testing with Loading
applied normal to the coating surface
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Conclusions
 This process is presented in this paper to coat HA powders
on Ti substrates at low temperature by laser surface engineering.
HA has very low absorption to Nd-YAG laser, therefore most laser
power is transmitted and scattered by HA powders and finally absorbed
by Ti powders and Ti substrate.
 In this fast heating and cooling process, HA powders are kept in low
temperature.
 This proves use HA to coating,coz good interfacial mechanical properties
has been achieved by using LSE technique.
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