Abstract
Tantalum (Ta) is a remarkable biological substance, with excellent corrosion resistance and biocompatibility. However, pure Ta coatings do not possess sufficiently high mechanical properties, especially wear resistance. To improve the wear resistance of Ta, Ta2O5 reinforced Ta-based coatings were fabricated on Ta substrates using laser cladding with a direct pre-placed powder method. The microstructure of the coating was primarily the result of a monotectic reaction and can be interpreted using the Ta-O phase diagram. The results suggested that Ta-Ta2O5 graded coatings can be fabricated on Ta substrates by controlling the amount of melting of the Ta substrate and/or adjusting the oxygen level of the processing chamber during laser cladding. The corrosion and wear resistances of the composite coating were higher than those of the uncoated Ta material when free corrosion potential, corrosion current density and wear track width were considered.
Highlights
Metal implants are subject to corrosion and fretting in biological environments, the release of metal ions and wear products appears to be unavoidable
It is considered important that the high solidification rates of the laser cladding process avoided the transformation of the high-temperature tetragonal (α) phase to the low-temperature orthorhombic (β) phase, because such a transformation is accompanied with a volumetric change
Cracks were not observed in the coating (Figure 3), no crack was found at the interface between the coating and the Ta substrate
Summary
Metal implants are subject to corrosion and fretting in biological environments, the release of metal ions and wear products appears to be unavoidable. For PVD methods, since the processes are normally carried out at relatively low temperatures, only a physical rather than a chemical bond is produced at the interface and this can result in weak coating adhesion [6]. Recognising these limitations, it is considered that laser cladding is a promising alternative method for fabricating relatively thick biocompatible metallic coatings.
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