Effect of hafnium micro-addition on precipitate microstructure and creep properties of a Fe-Ni-Al-Cr-Ti ferritic superalloy

(Left) Plot of steady-state strain rate vs. applied stress for compression creep tests at 700 °C showing that adding 1.5 or 2 wt%Ti to a Fe-Ni-Al-Cr ferritic steel drastically increases creep resistance. When further adding 0.5 wt% Hf, the creep resistance drops. (Right) Dark-field TEM micrograph of Ti- and Hf-modified steel aged at 700 °C showing B2 precipitates (green) containing L21 sub-precipitates (red).316