Axial suspension plasma sprayed hydroxyapatite coatings: Understanding the relationship between process parameters, microstructure and properties

Axial suspension plasma spraying (ASPS) is a recent addition to the plasma spraying technique to produce multifunctional advanced coatings. The present work explores the use of this process to coat thin, continuous and adherent Ca₅(PO₄)₃OH (hydroxyapatite, HA) coatings. Current work presents the role of process parameters on the evolution of microstructure and emanating adhesion strength. Three different HA coatings were deposited (fine-HA, coarse-HA, and fine-HA mixed with bioglass) on a real-life Ti–6Al–4V biometallic substrate. The effect of HA particle size and solid-loading (HA and bioglass) has been elicited on the evolution of microstructure. Phase-characterization has shown the retention of hydroxyapatite phase in the deposited coating, whereas the adhesion strength of HA-coating has reduced from ~40 MPa to ~13 MPa with the addition of bioglass. This work concludes that ASPS can potentially deposit thin HA coatings (< 50 µm) with high adhesion-strength as well as high crystallinity.

Keywords: Axial suspension plasma spraying; Hydroxyapatite; Bioglass; Adhesion Strength

Ideally, the HA coating should have characteristics like low porosity, high cohesive strength, good adhesion to the substrate, a high degree of crystallinity and high chemical purity and phase stability.

HA suspension was obtained commercially, whereas the other two were made indigeneously.