Effect of vitreous enamel coating on the oxidation behavior of Ti6Al4V and TiAl alloys at high temperatures

Vitreous enamel coating is a promising candidate as a high temperature protective coating for titanium (Ti)-based alloys due to its high thermo-chemical stability, compatibility, and matching thermal expansion coefficient to the substrates. Vitreous enamel coating is economically attractive because of its low cost and easy handling. The oxidation behavior of Ti6Al4V (at 700 degrees C) and Ti-48Al (at 800-900 degrees C), with and without the vitreous enamel coating exposed to air, are investigated in this article. The results show that the vitreous enamel coating could markedly protect the substrate (Ti6Al4V and Ti48Al) from oxidation at elevated temperatures. In comparison, the TiAlCr coating might not provide long-term protection for the Ti6Al4V alloys due to the heavy interfacial interdiffusion at high temperatures, although a protective Al2O3 scale could form at the initial oxidation stage. The vitreous enamel coating remains intact, uniform, compact, and adhesive to the substrate, however, with undetectable interfacial reaction after oxidation. It is also worth noting that some new phases form in the coating during oxidation at 900 degrees C, although the protectiveness of the coating seems to be unaffected.