Micro- and nano-testing of calcium phosphate coatings produced by pulsed laser deposition

Micro- and nano-testing methods have been explored to study the thin calcium phosphate coatings with high adhesive strength. The pulsed laser deposition (PLD) technique was utilised to produce calcium phosphate coatings on metal substrates, because this type of coatings exhibit much higher adhesive strength with substrates than conventional plasma-sprayed coatings. Due to the limitations of the conventional techniques to evaluate the mechanical properties of these thin coatings (1 microm thick), micro-scratch testing has been applied to evaluate the coating-to-substrate adhesion, and nano-indentation to determine the coating hardness and elastic modulus. The test results showed that the PLD produced amorphous and crystalline HA coatings are more ductile than titanium substrates, and the PLD coatings are not delaminated from the substrates by scratch. Also, the results showed that the crystalline HA coating is superior in internal cohesion to the amorphous one, even though the lower elastic modulus of amorphous coating could be more mechanically compatible with natural bone.