The corrosion behavior of Co-Cr-Al alloys exposed to mixed oxygen-sulfur atmospheres at 900 °C

Three Co-8Cr-xAl alloys (x = 0, 3, 5 wt.%) were exposed to three mixtures (Gas 1: H2-CO2, Gases 2 and 3: H2CO2-H2S) at 900 degrees C for 20 h. Gas 1 produced external chromia scales (plus internal alumina for Co-8Cr-3/5Al). Gas 2, with p(S2) below stability of Co sulfides, favored a transition from external chromia scales, observed in Gas 1, to exclusive external alumina scales for both Co-8Cr-3/5Al alloys. Conversely, Gas 3 was very aggressive for both Co-8Cr and Co-8Cr-3Al, forming a liquid Co-S phase, while with Co-8Cr-5Al it still formed external Al2O3 scales. Al additions improved the alloys resistance to the sulfur attack.

Automated summary

The study reveals the different behaviors of various alloys under different atmospheres, and the addition of aluminum improves the alloys' resistance to sulfur attack.