Experimental study of thermal expansion and phase transformations in iron-rich Fe-Al alloys

A series of Fe-Al alloys with various contents of aluminium (from 1 to 10 weight percent) was investigated by X-ray diffraction. The unit cell parameters and molar volumes of these alloys were measured at ambient conditions. The thermal expansions of two alloys (with 5 and 10 weight % Al) were obtained in the temperature range of 293–1370 K. The specimen was heated by passing an electrical current through the sample. The sample consists of a carbon strip as a heater and a Fe-Al alloy powder pressed onto its surface. A Pt-13% Rh thermocouple was used for temperature determination. In order to prevent oxidation of the specimen, the experiments were carried out in an argon-hydrogen flow. The spectra were analyzed and unit cell parameters at different temperatures were calculated using the General Structural Analysis System (GSAS) program. The phase transformation from bcc to fcc structure in the Fe-5%Al alloy was observed at temperatures between 1203(5) and 1238(5) K; the Fe-10%Al alloy transformed to a structure with a primitive cubic lattice at temperatures above 1300 K.