Effects of early transition metal solutes on the D03-B2 critical temperature of Fe3Al

The effects of dilute concentrations of the ternary solutes Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W on the critical temperature of the D0₃-B2 transformation in Fe₃Al were measured by differential thermal analysis (DTA). Additional studies by X-ray diffractometry showed that Mo, Ta, and W atoms occupied predominantly the 4(b) Wyckoff sites in D0₃-ordered Fe₃Al. Most solutes caused an increase in the D0₃-B2 transformation temperature, which was approximately linear in the limit of dilute solute concentrations. The efficacy of a particular ternary element in raising the D0₃-B2 transformation temperature was shown to be related to its metallic radius. We argue that the energetics of atom size mismatch are the major cause of the effects of ternary solutes on the D0₃-B2 transformation temperature of Fe₃Al.