Influence of Alloying with Tantalum on the Mechanical Properties and Corrosion Behavior of Ti-6Al-7Nb-xTa Cast Alloys

Abstract The Ti-6Al-7Nb (Ti67) alloy is a modified version of Ti-6A-4V (Ti64) alloy, a commercially used biomaterial for implantology. In the current investigation, four Ti67-based alloys were prepared with different tantalum (Ta) contents (0.0, 1.5, 2.5, and 3.5 wt.%) using vacuum arc melting. X-ray diffraction (XRD) and scanning electron microscopy and energy-dispersive X-ray analysis (SEM-EDX) were used to understand the microstructure changes due to Ta additions. The corresponding influence of microstructure on the mechanical properties was evaluated in terms of Young's modulus, hardness, and wear resistance measurements. The corrosion characteristics of the alloys in simulated body fluid (SBF) were also investigated. Phase identification revealed that, besides α- and β- Ti which are the main phases of cast Ti67 alloy, Ta x Ti y compounds formed with Ta addition. Young's modulus decreased from 131.8 for Ti67 to 122.0 GPa with 3.5 wt.% Ta. Hardness increased from 327.4 for Ti67 to 378.8 HV at 3.5 wt.% Ta. Alloying Ti67 with Ta enhanced wear resistance, benefiting components vulnerable to surface wear and friction. Also, the addition of 1.5 wt.% Ta reduced the corrosion rate from 31.03 (Ti67) to 5.69 μm/y and increased the polarization resistance from 11.77 to 54.26 μΩ. However, increasing the amount of Ta beyond 1.5 wt.% adversely affected Ti67-xTa alloys' resistance to corrosion.