Growth kinetics and corrosion properties of pack-borided Ti-5Al-2.5Sn alloy

In this work, the pack boriding method was used to treat the surface of Ti-5Al-2.5Sn (TA7) titanium alloy. The boriding temperatures were selected as 975 °C, 1000 °C, 1025 °C, 1050 °C, and 1075 °C, and the boriding time was 6, 8, 10, and 12 h. The phase and microstructure of the boride layer were analyzed using X-ray diffraction and scanning electron microscopy. The corrosion resistance was studied through polarization curves and electrochemical impedance spectroscopy, and the growth kinetics of the boride layer was modeled using the diffusion model of d2 = Dt and the parabolic model. After boriding at 1075 °C for 12 h, the thickness of the boride layer reaches the maximum with a maximum thickness of 45.75 μm. In addition, the diffusion model of d2 = Dt is more accurate in predicting the thickness of boride layer. The activation energies of boron diffusion in TiB2, TiB, and TiB2 + TiB layers are 94.78, 221.15, and 256.90 kJ/mol, respectively. Finally, the corrosion properties of borided TA7 alloy in NaCl and H2SO4 solutions were also discussed. •At 1075 °C-12 h, the maximum thickness of boride layer reaches 45.75 μm.•B is prone to diffuse in TiB2 layer on TA7 alloy due to its low activation energy.•Corrosion resistance of TA7 alloy can be improved by boride layer.