Comparison of laser cladding properties of tantalum and tantalum pentoxide powders on titanium substrates

Abstract

Tantalum (Ta) has excellent mechanical properties, biocompatibility, and corrosion resistance. However, its application is limited by its high cost. Tantalum pentoxide (Ta2O5), a stable oxide of Ta, is a key role of Ta surface with excellent biological properties and corrosion resistance and has the advantage of a lower cost. In this study, Ta and Ta2O5 powders were preplaced on titanium (Ti) substrates and irradiated by a diode laser to form single-layer single-pass coatings. For comparison purposes, the scanning process was performed using a range of laser powers (1000, 1500, and 2000 W) and scanning speeds (3–5, 4.5–7.5, and 6–10 mm/s). The Ta coatings showed no surface cracking. However, spherical pores were observed near the fusion line of the coating with the substrate in some samples. The porosity increases with the decrease of laser powers and the scanning speeds. The formation of these pores was attributed mainly to the evaporation of the Ti substrate during the cladding process and the subsequent entrapment of the vapor bubbles within the coating. The Ta2O5 coatings showed almost no pores but exhibited few transverse cracks on the coating surface as a result of the thermal expansion coefficient mismatch between the ceramic coating and metallic substrate. For all of the coatings, the coating hardness was significantly higher than that of the substrate. The Ta2O5 coatings (580–700 HV) showed a higher hardness than the Ta coatings (350–400 HV). Moreover, the coating hardness remained approximately constant through the coating depth, whereas that of the Ta coatings showed a notable reduction with an increasing distance from the coating surface.