Hot Corrosion of Ti-Based Intermetallics with Coatings in NaCl+ (Na,K)2SO4 Melts at 750oC

In this study, the hot corrosion of TiAl, TiAlNb, and Ti3AlNb intermetallics with or without enamel coating and sputtered TiAlCr coating in (Na, K)2SO4 + NaCl melts at 750oC is investigated. The interfacial reaction between enamel and those alloys during hot corrosion has also been evaluated. The results indicate that severe corrosion of bare alloys occurs due to the self catalysis chlorination and sulfidation of metallic components. TiAlNb shows the best corrosion resistance among the three examined alloys. The sputtered TiAlCr coating fails to protect the substrate from hot corrosion due to the rapid volatility of chromium chlorides other than the formation of protective Al2O3 scale. The enamel coating could protect Ti-base alloys from hot corrosion due to its thermal stability and matched thermal expansion coefficient with the substrates. However, the interfacial reaction and selective oxidation of aluminum between enamel coating and Tialloys substrate under a low oxygen partial pressure decreases the stability of enamel coating with increasing the activity of aluminum of alloys.