High temperature corrosion of TiAlCrNb alloy with TiAl2 out-of-pack coating in N2-O2-SO2-HCl environments

In this article results of microstructural analysis and corrosion resistance tests of 48-2-2 alloy (TiAlCrNb) with and without protective coating were presented. The aluminide coating was deposited by out-of-pack method on the base alloy. The thickness of the coating was 10[mi]m and it was composed of TiAl2 phases. The corrosion resistance tests of the base alloy with and without the protective coating have been conducted at 600°C in the at-mosphere containing nitrogen, with the addition of 9% of O2, 0,08% of S02 and 0,20% of HCl. The tests lasted for 1250h. The aim of the conducted tests was to determine the mass gain of the samples in the given conditions and to identify the corrosion products, using X-ray phase analysis and EDS chemical content microanalysis. The detailed investigation has been done after 25,50, 100, 150, 250, 500,750, 1000 and 1250h of testing. As clearly indicated by the results of investigations, aluminide coating improves the corrosion resistance of TiAl alloy in the conditions of the performed test. The corrosion-resistance-enhancing effect of this type of diffusion coatings was attributed to the surface layer consisting of TiAl2.