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

Tantalum (Ta) has excellent mechanical properties, biocompatibility, and corrosion resistance. However, its application is limited by its high cost. Tantalum pentoxide (Ta 2 O 5 ), 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 Ta 2 O 5 powders were pre-placed on titanium (Ti) substrates and irradiated by a diode laser to form single-layer single-pass coatings. 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 increased with a decreasing laser power and scanning speed. 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 Ta 2 O 5 coatings showed almost no pores but exhibited a small number of transverse cracks on the coating surface because of the thermal expansion coefficient mismatch between the ceramic coating and the metallic substrate. For all of the coatings, the coating hardness was significantly higher than that of the substrate. The Ta 2 O 5 coatings (580–700 HV) showed a higher hardness than the Ta coatings (350–400 HV). Moreover, the coating hardness remained approximately constant throughout the coating depth, whereas that of the Ta coatings decreased significantly with an increasing distance from the coating surface.