Effect of Cr and Y on the microstructure and mechanical properties of Fe-Cr-Al alloys during corrosion-aging in superheated steam at 500 C

The alpha-alpha' phase separation of Fe-Cr-Al alloys during long-term service at 475-500 degrees C may lead to the increase of strength and hardness and the decrease of ductility, which will limit the application of Fe-Cr-Al alloys as accident tolerant fuel (ATF) cladding material. The mechanical behavior and microstructure evolution of Fe-12Cr-5Al, Fe12Cr-5Al-0.01Y, Fe-20Cr-5Al and Fe-20Cr-5Al-0.02Y (wt%) alloys in 500 degrees C superheated steam for 2000 h have been investigated by tensile test, Vickers hardness measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), three-dimensional atom probe (3DAP) and thermodynamic calculations. Results show that increasing the Cr content may refine the grain and improve tensile strength of the alloy, while adding trace Y has negligible effect on the grain size and tensile strength of the alloy; the corrosion-aging hardening of 20CrY and 20Cr alloys is attributed to the alpha-alpha' phase separation, which is closely related to the high content of Cr in the alloy. The addition of trace Y promotes the nucleation and growth of alpha' phase in alloys with the content of 20%Cr during the corrosion-aging process but has insignificant influence on the mechanical properties of the alloy.