Atmospheric plasma sprayed Ti/HAp duplex coatings on CFR-PEEK substrates for implant applications: influence of process parameters on mechanical and microstructural characteristics

Polyetheretherketone (PEEK) is a high-performance thermoplastic valued for its biocompatibility and mechanical properties, especially when reinforced with carbon fibre (CFR-PEEK), making it suitable for load-bearing implants. However, its bioinert, hydrophobic surface limits osseointegration. To address this, titanium/hydroxyapatite duplex coatings were applied to CFR-PEEK using atmospheric plasma spraying (APS). Prior to coating, substrates were roughened by alumina sandblasting. A titanium bond coat was followed by a hydroxyapatite layer, deposited under varying plasma currents (600-700 A) and spray distances (100-150 mm). The effects of these parameters on coating adhesion, morphology, porosity, and crystallinity were assessed via tensile tests, SEM, and XRD. Results showed that increased spray distance enhanced surface roughness but reduced coating thickness and crystallinity, while higher current increased thickness but decreased roughness and crystallinity. The highest tensile adhesion strength (33.79 ± 1.52 MPa) was achieved at 650 A and 125 mm meeting international standards without damaging the substrate.