High-energy ion beam implantation of hydroxyapatite thin films grown on TiN and ZrO2 inter-layers by pulsed laser deposition

Abstract

Current drawbacks in the hydroxyapatite (HA) thin film production for applications in bone surgery are their poor mechanical strength and limited adherence. This paper presents the ion beam implantation technique as an efficient method to improve the mechanical characteristics of HA films. Crystalline films of HA were grown by pulsed laser deposition, using a KrF* excimer laser (λ=248 nm, τ⩾20 ns). The depositions were performed from pure HA targets on Ti–5Al–2.5Fe alloys coated with TiN or ZrO2 buffer layers. Samples were then implanted with Ar+ ions of high-energy (1.5 MeV) at a dose of 1016 cm−2. The as-deposited and implanted films were characterized by light microscopy and energy dispersive X-ray spectrometry. The mechanical properties of films were studied by nanoindentation and nano-scratch techniques using a Berkovich indenter tip. Films become harder and exhibit a higher Young modulus after implantation. The best values (5 GPa hardness and 130 GPa Young modulus, respectively) were obtained for the implanted films grown on TiN. An influence of the buffer layer nature on the mechanical behavior of films was observed. Films grown on ZrO2 are brittle and crack at moderate load (∼12 mN) during scratch while these ones deposited on TiN successfully withstand loading. Residual stresses occur into the HA/ZrO2 structure during processing and ion bombardment.