High-Temperature Oxidation Behavior of Al-Modified Boronized Coating Prepared on Ti-6Al-4V by Thermal Diffusion

The Al-modified boronized coating on Ti-6Al-4V was successfully fabricated to protect the alloy from oxidation by the neutral salt bath method. The thickness of the Al-modified boronized coating (69.8 ± 2 μm) is 36% thicker than that of the simple-boronized coating (51.3 ± 1.5 μm). To evaluate the oxidation resistance, the high-temperature oxidation behavior was analyzed by the high-temperature oxidation experiment at 700 and 900 °C. The results show that after oxidation, the Al-modified boronized coating was mainly comprised of TiO₂, Al₂O₃, Al₃Ti, Ti₃B₄ and TiS phases, and the surface of the Al-modified boronized coating is smoother and denser. The thickness of the oxide layer of the Al-modified boronized coating is the minimum, which is 11 ± 0.3 μm and 13 ± 0.5 μm at 700 and 900 °C for 60 h, respectively. The average oxidation rate of the Al-modified boronized coating is − 0.003 and 0.022 mg cm⁻² h⁻¹ due to the formation of Al₂O₃ on the surface. Therefore, adding Al into the simple-boronized coating is beneficial for the high-temperature oxidation resistance.