Thermal Sprayed Bioceramic Coatings: Nanostructured Hydroxyapatite (HA) and HA-Based Composites - Biological and Biomedical Coatings: Processing and Characterization - page 167

overall porosity of a bulk coating. Melt state and velocity of the sprayed particles during
spray may play the most important role in determining the overall porosity through their
influence on pore structure.

MechanicalPropertiesandRelationshipbetween
NanostructureandProperties
Due to the anomalous inhomogeneous-layered structure, the coatings show a signifi-
cant dependence of their mechanical performances on the microstructure. Influence of
the nanostructures on the mechanical properties such as adhesive strength and Young's
modulus is always an important issue that required significant research efforts prior to
the applications of the coatings. It was found that for the nanostructured HA coatings the
nanostructures contribute to increased Young's modulus values (Li et al. 2006). With the
increase of the melted area in the spayed particles (hence the relative content of the nano-
structures, HVOF3 vs. HVOF1 in Figure 4.24), the Young's modulus of the corresponding

80

(a)

p < 0.05
p < 0.05

p < 0.05

60.11

60

55.26

50.39

41.45

40

20

0

HVOF1 HVOF2 HVOF3 Plasma

Specimen designation code

(b)

40

30

20

10

0

HVOV1 HVOF2 HVOF3 Plasma

Coating designation

FIGURE 4.24
(a) Young's modulus of the coatings, and (b) adhesive strength of the coatings (HVOF1, HVOF HA coating [50
± 10 μm powder]; HVOF2, HVOF HA coating [40 ± 10 μm powder]; HVOF3, HVOF HA coating [30 ± 10 μm
powder]; Plasma, plasma HA coating (50 ± 10 μm powder). (From Li, H., Khor, K.A., Surf. Coat. Technol. , 201,
2147-2154, 2006. With permission.)