The Effects of Chromium on the High Temperature Corrosion of Ni-Cr Alloys Exposed to Calcium Sulfate

Calcium and sulfur rich deposits have been linked to failure of turbine components as a consequence of high temperature exposures (> 1000°C). There are only limited studies on the effects of these deposits on the degradation behavior of turbine alloys. To gain further understanding of this phenomenon, a systematic study was undertaken with model binary nickel-chromium alloys. Three alloys with different chromium contents – low, medium, and high – represented by Ni-5Cr, Ni-10Cr and Ni-18Cr, were exposed to CaSO 4 -deposit-induced corrosion in the 900–1100°C temperature range. At 1000 and 1100°C, the decomposition of CaSO 4 led to the formation of calcium chromates and chromium sulfides. At the lower temperature, 900°C, there was only limited decomposition of CaSO 4 , allowing the formation of a continuous Cr 2 O 3 scale was able to form.