Properties and site substitutions for ternary chromium additions to B2 iron aluminides

The equiatomic and iron-rich ordered iron aluminides are potential medium temperature materials because of their low cost and good elevated temperature properties. However, their chief drawback is their brittleness at room temperature. Attempts have and are being made to increase their ductility by alloying. It has also been established that the site preference of the ternary element could affect the mechanical properties of these aluminides. A study was made of the site substitution of Cr in the B2 FeAl using the variable x-ray energy of a synchrotron source. Seven compositions were chosen of which three were binary FeAl alloys. It was found that Cr had a clear preference for the Al site for all the compositions. The amount of Al on the Fe site varied considerably with specimen composition for the ternary alloys but was relatively independent of composition for the binary alloys. These data represent one of the first systematic studies of the site preference of a ternary addition to a binary compound. Improvements in the sample preparation and data analysis provided significant reductions in uncertainties. These meaningful values of site preference were not strongly correlated with hardness but reflected the chemistry of the binary phases. The hardness values, after cooling from a low - temperature anneal were insensitive to composition except for the Fe₅₁Al₄₉ alloy which showed a much higher hardness.