Anti-oxidation characteristics of Cr-coating on surface of Ti-45Al-8.5Nb alloy by plasma surface metallurgy technique* *Project supported by the National Natural Science Foundation of China (Grant No. 51601122), the 2019–2020 Intergovernmental Cooperation Projects in Science and Technology of the Ministry of Science and Technology, China (Grant No. CB02-03), the Science and Technology Major Project of Shanxi Province, China (Grant No. 20181102013),

Abstract

TiAl-based alloys have received extensive attention recently due to their excellent properties. However, the weak oxidation resistance at temperatures higher than 800 °C can limit their further high-temperature structural applications. To improve the oxidation resistance of a high-Nb-content γ-TiAl alloy (Ti-45Al-8.5Nb, in units of at.%), a chromium (Cr) coating is prepared by using the plasma surface alloying technique, separately, at 800 °C and 1000 °C. The x-ray diffraction (XRD) patterns reveal that an oxide surface layer consisting of Cr2O3, Al2O3, and TiO2 is produced on the Cr-coated Nb containing γ-TiAl substrates during the initial oxidation. However, the Cr2O3 is dominated in the oxide surface layer after being isothermally oxidized for 300 h. The oxidation kinetic curves are composed of a parabolic law stage (≤ 90 h) and a biquadratic law stage (≥ 90 h), fit by weight–gain curves. Due to diffusion in the fabrication process and oxidation process, the Cr-coated specimens have an adhesion force after being isothermally oxidized, specifically 69 N for a specimen after oxidation for 300 h. These results demonstrate that the Cr coating enhances the oxidation resistance and adhesion of a Ti-45Al-8.5Nb alloy, which may provide a new feasible scheme for designing oxidation protection layers.