High-temperature steam oxidation of (Ti, Mo)C-forming FeCrAlY alloy

Abstract

High-temperature steam oxidation testing is conducted at 1200 and 1300 °C to evaluate the oxidation resistance and characterize the oxide of the (Ti, Mo)C-forming FeCrAlY alloy developed as a candidate for accident-tolerant fuel-cladding materials in nuclear power plants. The oxidation behavior on both temperatures was investigated using X-ray diffraction, scanning, and transmission electron microscopies. The oxidation behavior of the new alloy indicates a temperature dependency: at 1200 °C, TiO2 and Y2Ti2O7 are seen on the outermost oxide layer, whereas no Ti-rich oxide is detected at 1300 °C, but and Y3Al5O12 are observed, which are typical oxides in carbide-free FeCrAlY alloys. On the TiO2 surface, water molecules can become dissociated, and the products of the dissociation can create more oxygen vacancies, which in turn can lead to a porous oxide layer with voids and a higher oxidation rate when compared with FeCrAlY alloys. However, at 1300 °C, Ti diffusion is efficiently blocked by Y segregation along oxide grain boundaries due to larger oxide grains and less intersections between the oxide grain boundaries and the oxide/metal interface. The oxidation resistance of (Ti, Mo)C-forming FeCrAlY is superior to that of the Zr alloy, which makes it a suitable candidate for accident-tolerant fuel-cladding materials from the perspective of high-temperature steam oxidation.