Molten salt vapour corrosion of Ti–Al–Ag intermetallics

The effect of Ag addition on the hot corrosion behaviour of γ-TiAl has been studied. Hot corrosion tests were performed with a salt mixture consisting of 80 wt.% Na2SO4+20 wt.% NaCl (melting point ∼700 °C). The specimens were suspended in the salt vapour at 800 °C for 200 h. Ti–48Al–2Ag showed the best corrosion resistance. It is believed that Ag can promote the formation of a ternary compound, Ti50Al30O20, in the subscale depletion layer of γ-TiAl intermetallics. Subsequently, a long-term protective scale rich in alumina is formed. Electron microscopy and X-ray diffraction were used to study the morphologies, compositions, and phases of the corrosion products. The corrosion mechanisms were discussed based on the experimental results.