Effects of Al addition on Vickers hardness increase by thermal aging of Fe-Cr-Al alloys; Evaluation by systematic experiments, machine learning modeling, and first-principles calculations

Abe, Yosuke  ; Tsuru, Tomohito   ; Fujita, Yohei*; Otomo, Masahide*; Sasaki, Taisuke*; Yamashita, Shinichiro   ; Okubo, Nariaki   ; Ukai, Shigeharu  

We investigated the effect of Al addition on the formation of phase in Fe-Cr-Al model alloys by thermal aging. The Vickers hardness tests and a machine learning model indicate that the formation of the phase is promoted by low Al additions and suppressed by high Al additions. First-principles calculations, which indicate that Cr-Al-vacancy pairs are more stable than Cr-Cr pairs and that including Al atoms during phase nucleation may be energetically advantageous. On the other hand, the formation of Al-Al pairs was very unstable. The formation of Al-Al pairs near the interface can be avoided when the amount of Al addition is small. However, it is inevitable when the amount of Al addition is significant, leading to the instability of the phase.