In-depth study of mechanical and physico-chemical properties of calcium phosphate coatings obtained by laser surface cladding

Abstract

The combination of the mechanical properties of light metal alloys (Ti6Al4V) and the resemblance of the human tissues of the bioceramics (calcium phosphate ceramics) assures the bearing of huge mechanical loads and the osteointegration of orthopaedical implants. In order to be entirely successful when the mechanical properties of the bulk material and the physico-chemical properties of the bioactive surface are combined, the application of laser cladding was required. Laser cladding is well known as a technique capable to produce a strong fusion bond between the coating and the substrate. Nevertheless the physico-chemical properties of the coating have to be also guaranteed. In this work, the ceramic coatings were obtained over Ti6Al4V alloy substrates by the application of a fibre optic guided Nd:YAG laser beam and a flow of the hydroxyapatite precursor material.The thickness of the coatings was in the hundred of microns range and in-depth morphology and composition did not keep uniform. A study of the mechanical properties was carried out by nanoindentation and the physico-chemical properties of the material were obtained by XRD and EDX. The data of the in-depth analysis were correlated to put in evidence the gradual profile of the elastic modulus from the top of the surface of the coating to the substrate. Also an inverse gradual profile of the coating composition from the top of the coating to the substrate was evaluated and related to the mechanical properties described.The combination of the mechanical properties of light metal alloys (Ti6Al4V) and the resemblance of the human tissues of the bioceramics (calcium phosphate ceramics) assures the bearing of huge mechanical loads and the osteointegration of orthopaedical implants. In order to be entirely successful when the mechanical properties of the bulk material and the physico-chemical properties of the bioactive surface are combined, the application of laser cladding was required. Laser cladding is well known as a technique capable to produce a strong fusion bond between the coating and the substrate. Nevertheless the physico-chemical properties of the coating have to be also guaranteed. In this work, the ceramic coatings were obtained over Ti6Al4V alloy substrates by the application of a fibre optic guided Nd:YAG laser beam and a flow of the hydroxyapatite precursor material.The thickness of the coatings was in the hundred of microns range and in-depth morphology and composition did not keep uniform. A study of the m...