Thermal performance determination of binary Fe-Al alloys at elevated temperatures

The thermal expansion and thermal diffusion properties of Fe−Al alloys were measured using dilatometric and laser flash methods. At two allotropic transformation temperatures, the length change of the rapidly solidified pure Fe by injection casting deviates from that of the pure Fe by heating-cooling processing in a dilatometer. The ferro-/paramagnetic transition and second order transition do not influence the thermal expansion behaviors of Fe−Al alloys as temperature increases from 473 to 1373 K. The thermal expansion coefficients of Fe₇₀Al₃₀, Fe₆₀Al₄₀and Fe₅₅Al₄₅alloys are apparently larger than those of Fe₂₅Al₇₅and Fe₉₀Al₁₀alloys. Once temperature exceeds 877 K, the thermal expansion coefficients of Fe-Al alloys are enhanced with the increase of Al content, except for Fe₂₅Al₇₅alloy owing to the large packing factor of FeAl₃crystal structure. In the temperature range from 309 to 877 K, the thermal diffusivity as a function of temperature decreases in the sequence of Fe₉₀Al₁₀Fe₅₅Al₄₅, Fe₆₀Al₄₀, Fe₇₀Al₃₀and Fe₂₅Al₇₅, and their values are lower than that of pure Fe at the same temperatures. As temperature increases, the thermal diffusivity values of Fe−Al alloys increase, except that of Fe₉₀Al₁₀alloy decreases in the temperature range from 294 to 979 K and then increases once temperature further increases to 1078 K because of the ferro-/paramagnetic transition. Their thermal expansion coefficient and thermal diffusivity serve as linear or polynomial functions of temperature.