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The effect of the pulsed electron beam (PEB) treatment on the structure and morphology of the hydroxyapatite (HA) coating deposited on the surfaces of titanium substrates by radio frequency magnetron sputtering was elucidated. The structure, composition and morphology of the samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results collected from SEM experiments demonstrated that the HA film was smooth and featureless. The samples were irradiated by PEB using an electron beam energy density of 0.1 J cm-2, electron beam pulse duration of 50 ms, pulse repetition frequency of 5 Hz, and number of pulses N=50 and N=150. After PEB treatment with N=50, the coating exhibited a much finer uniform surface morphology, playing a crucial role in the enhancement of the mechanical properties of the HA-coated titanium substrate. The surface of the HA film treated with N=150 was still smooth and feature less. The XRD data demonstrated that PEB treatment of HA films produced only a slight decrease in the HA phase content. The combination of these two techniques opens the possibility of preparing high quality HA layers.

Silicon-doped hydroxyapatite-based (Si-HA) coatings were deposited via radio frequency (RF) magnetron sputtering on the surface of titanium that was treated with a pulsed electron beam. This study aimed to evaluate the effect of Si doping on the structure and mechanical properties of thin HA films. The content of the silicon was 1.2 and 4.6 at.% for the coatings prepared using the Si-HA precursor powders with a chemical formula Ca10(PO4)6 − x(SiO4)x(OH)2 − x where, x = 0.5 and 1.72. Pure HA (Ca10(PO4)6(OH)2) coatings were deposited for comparison. The as-deposited films were analysed with respect to their composition, state of chemical binding and microstructure using XPS, FTIR, XRD, and SEM. We hypothesized that the addition of Si would affect the mechanical features of the coatings due to microstructure changes. The effect of the introduction of Si on the nanohardness and the Young's modulus as well as the adhesion strength and scratch resistance of the HA coating was investigated using nanohardness testing and a scratch test, respectively. Examination of the coating microstructure using SEM and AFM revealed that Si doping influenced the surface morphology and led to a smaller grain size. The tendency to form an amorphous structure also increased with an increase in the Si content. A monotonous decrease in both the nanohardness and the elastic modulus was observed with an increase in the Si content. A maximum nanohardness of ~ 7 GPa was obtained for the Si-free HA coating, whereas the hardness decreased to ~ 4.3 GPa for the films with a Si content of 1.2 at.%. The addition of 4.6 at.% Si to the HA coating resulted in a reduction in the elastic modulus, whereas the nanohardness was very similar to that of the uncoated substrate. The adhesion behaviour of the coatings demonstrated different responses. In the case of pure HA coatings, failure occurred due to the low cohesion of the coating, whereas the crystalline Si-HA coatings with a Si content of 1.2 at.% deformed plastically without crack formation and without detaching from the titanium substrate, which resulted in a greater coating stability.