Deposit-Induced Corrosion of Ni-Cr Alloys in Calcium-Based Salt Mixtures

Abstract Corrosion of gas turbine components at high temperatures under salt deposits is a critical issue that adversely affects their performance and longevity. Calcium-containing compounds have been detected in the analysis of failed components. These compounds may have different origins, e.g., sand particles, salts from marine atmospheres, atmospheric pollutants, etc. The consequences of the reactions between the salt deposits and the alloy substrate can result in enhanced solute depletion, and removal/destruction of the external protective scale. In this presentation, the focus will be on the effect of chromium concentration, and process variables such as temperature, time, and atmosphere, on the deposit-induced corrosion of model Ni-Cr alloys. In this paper results from the exposure of Ni- 5 Cr and Ni-18 Cr alloys are presented. These alloys were exposed to thin films of calcium sulfate combined with sodium chloride. The post-test coupons were characterized using optical microscopy, x-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. Overall, the high chromium alloy (Ni-18 Cr) showed evidence of more extensive attack at 1000°C relative to the low chromium alloy (Ni-5 Cr) after 100 hours of exposure in both air and SO2/air mixtures containing 10 ppm SO2.