Influence of composition and heating schedules on compatibility of FeCrAl alloys with high-temperature steam

TL;DR

This study investigates how alloy composition and heating protocols affect the oxidation resistance of FeCrAl alloys in high-temperature steam, revealing conditions that lead to catastrophic oxidation and identifying factors that improve high-temperature stability.

Contribution

It provides new insights into optimizing FeCrAl alloy compositions and heating schedules to enhance their high-temperature steam oxidation resistance for nuclear fuel cladding.

Findings

Higher Cr and Al content increases maximum compatible temperature.

Slower heating rates reduce catastrophic oxidation risk.

Yttrium doping enhances protective alumina scale formation.

Abstract

FeCrAl alloys are proposed and being intensively investigated as alternative accident tolerant fuel (ATF) cladding for nuclear fission application. Herein, the influence of major alloy elements (Cr and Al), reactive element effect and heating schedules on the oxidation behavior of FeCrAl alloys in steam up to 1500{\deg}C was examined. In case of transient ramp tests, catastrophic oxidation, i.e. rapid and complete consumption of the alloy, occurred during temperature ramp up to above 1200{\deg}C for specific alloys. The maximum compatible temperature of FeCrAl alloys in steam increases with raising Cr and Al content, decreasing heating rates during ramp period and doping of yttrium. Isothermal oxidation resulted in catastrophic oxidation at 1400{\deg}C for all examined alloys. However, formation of a protective alumina scale at 1500{\deg}C was ascertained despite partial melting. The occurrence of catastrophic oxidation seems to be controlled by dynamic competitive mechanisms between mass transfer of Al from the substrate and transport of oxidizing gas through the scale both toward the metal/oxide scale interface.