Gallium-Suboxide Attack of Stainless Steel and Nickel Alloys at 800–1200°C

Failure of furnace parts composed of stainless steel or nickel-base alloys has been observed following treatment of gallium-containing compounds at 800 to 1200°C. This work examines the effect of gallium suboxide (Ga2O) and gallium oxide (Ga2O3) on the chemical and mechanical properties of 304 SS, 316 SS, and Hastelloy C-276 in an effort to elucidate a failure mechanism. Results indicate that all three materials are subject to attack by gallium compounds. Elemental segregation, oxidation, and Ga uptake all occur following exposure. Ga2O gas appears to play the dominant role in alloy attack under reducing conditions. Increasing temperature is shown to increase the magnitude of attack, as measured by oxide thickness and gallium-metal uptake. Calculations of the system thermodynamics suggest that Cr, Mn, Si, and V alloying components are responsible for metal oxidation and concurrent gallium absorption. A homogeneous, large (>30 wt.%) gallium uptake resulted in brittle failure of 304 SS. Therefore, exposure to gallium compounds can result in premature failure of iron- and nickel-base structural alloys.