Biomedical Engineering Reference
In-Depth Information
4.3 Adhesion properties evaluation
Pull-out tests were conducted in order to evaluate the adhesion strength of the HA ceramics
coating. A schematic illustration of the pull-out testing method used is drawn in Fig.14. The
HA coated samples were embedded into an epoxy resin (Sumitomo 3M, Japan) placed in a
sample attachment. According to the supplier, the tensile and shear strength of the epoxy
resin used were measured to be approximately 29.4 and 11.8 MPa, respectively. And then
the protruding part of the HA coating was removed with a grinder and a knife. In order to
identify the crystals in the treated specimens, the removed HA coating material was applied
to power X-ray diffraction analysis (XRD; MX21, Mac Science, Japan) with Cu
K
radiation
40kV 40mA at a scanning speed of 3.00˚/min with a scanning range (2) from 10˚ to 40˚. The
microstructure of the coating surface was observed by scanning electron microscopy (SEM;
S4300, Hitachi, Japan).
The specimens were loaded with an Instron-type testing machine at a cross-head speed of
0.5mm/min until the Ti rods were pulled out entirely. The sample attachment was
connected to a universal joint. The upper part of the Ti rod was gripped with a manual
wedge grip and then loaded with the testing machine through a load-cell. The load
P
and
cross-head displacement were recorded during the tests. In order to evaluate the adhesion
properties of the HA coating on Ti rod quantitatively, the shear strength and fracture energy
were calculated from the results of the pull-out testing. The shear fracture strength, is
computed using the following equation:
P
dL
(3)
where
d
is the diameter of Ti rods(1.5mm),
L
is the embedment length of Ti rods,
P
is the
load. The fracture energy,
G
is calculated using the following equation:
A
c
A d
G
(4)
dL
0
where is the cross-head displacement and
A
is the area under the load versus cross-head
displacement up to the complete pull out displacement,
c
.
4.4 Results and discussion
As demonstrated in Fig.15, HA ceramic layers could be coated to the all surface of Ti rods at
the low temperature of 135˚C using the above-mentioned DC-HHP method. The thickness
of the HA coating layers could be controlled by the volume of the HA starting powder
placed in capsule I, and the thickness range achieved in this study was 10 m-1 mm. The
experimental results for the thickness of 50 m will be presented below. When the seal
tightness of capsules II was imperfect, the water placed in the vessel was observed to
penetrate into the inner space of the capsules and the HA coating could not be achieved. It
was critically important that the inner space of the capsules was vacuumed prior to the
hydrothermal treatment in order to check and ensure the seal tightness of the capsules.
XRD profiles of the HA coating layers are shown in Fig.16 for the different treatment times.
Only the peaks for HA are observed for the treatment time of 12 and 24 hours, whereas the
HA layer prepared with the treatment time of 3 and 6 hours includes the phases of the
starting materials or the precursors. Thus, it is understood that the treatment time longer
