Degradation of a TiAl-base alloy in hot salt environments

The investigated material was a two-phase (gamma+alfa2) titanium aluminide alloy (Ti-46Al-8Nb) with a fully lamellar structure. The specimens were contaminated either with Na2SO4 or NaCl or a mixture of the two salts, and subjected to thermal cycling in air at 700°C, 800°C or 900°C. The progress of degradation was followed by recording mass variations after consecutive 20-hour cycles. The overall duration of each test was 300 hours. The post-test examination included morphology, chemical and phase composition of the corrosion products, extent and type of alloy degradation. After the test, Ti and Al concentrations in the near-surface layer of the alloy were lower than in the bulk. The depletion zone was the widest in the case of specimens contaminated with sodium chloride. Numerous macrodefects were visible in this region. The Ti-46Al-8Nb alloy demonstrated poor resistance to hot corrosion.