Evaluation of mechanical properties of plasma sprayed HA coatings using the indentation technique

Mechanical properties of plasma-sprayed HA coatings deposited on Ti-6Al-4V substrates by varying two spray parameters were evaluated using the indentation technique. The content of amorphous phase (ACP) at coating interface or surface as measured by XRD increased both with increasing spray distance and/or plasma power and also from the coating surface toward the interface. The microhardness value, elastic response, and Young’s modulus (E) were found to be controlled by the compromise between porosity level and ACP content. The indentation fracture toughness (KC) of coatings mainly depended on the contents of recrystallized HA (RHA) and ACP, as well as on porosity level. The Knoop and Vickers indentation methods were used to estimate E and KC, respectively. The critical point at which no crack appears at the interface was determined by the interface indentation test, which was used to define the interfacial toughness (KCa) representative of the crack initiation resistance of the interface. KCa was found not to change in a simple manner with the two plasma parameters. The results indicate that the optimized values of ACP and RHA contents at the interface were the factors most influencing KCa values