Phase equilibria among η-Fe2Al5 and its higher-ordered phases

Phase equilibria among the eta-Fe2Al5 phase and its higher-ordered phases with the eta framework structure were determined experimentally. The solubility range of the eta phase at elevated temperature does not differ remarkably from that in previous studies, but this phase is found to undergo complicated phase transformations upon cooling. Four phases are present, namely eta',eta '',eta''' and eta(m), with higher-order atomic orderings in the c-axis chain sites of the orthorhombic crystal structure of the parent eta phase. The eta '' and eta''' phases form on the Al-poor and Al-rich sides, respectively, in equilibrium with the zeta-FeAl2 phase below similar to 415 degrees C and theta-Fe4Al13 phase below similar to 405 degrees C. The eta' and eta(m) phases become stable below 312 degrees C and 343 degrees C with the peritectoid reactions eta' -> eta(m) + eta''' and eta(m) -> eta + eta '', respectively. The eta phase is not stable below 331 degrees C with the eutectoid reaction of eta(m) + eta''' -> eta. On the basis of these findings, we unraveled the phase equilibria among the eta-Fe2Al5 phase and its higher-ordered phases with the. framework structure. [GRAPHICS]

Automated summary

Experimental determination of phase equilibria among the eta-Fe2Al5 phase and its higher-ordered phases revealed complex phase transformations during cooling, resulting in the formation of multiple phases.η'' and η''' phases form on the Al-poor and Al-rich sides, respectively, while η' and η(m) phases become stable below specific temperatures through peritectoid reactions. Additionally, the eta phase is found to be unstable below 331 degrees C due to a eutectoid reaction.