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 w eight percent) was investigated by X-ray diffraction. The unit cell paramet ers and molar volumes of these alloys were measured at ambient conditions. The thermal expansions of two alloys ( with 5 and 10 weight % Al) were obta ined in the temperature range of 293-1370 K. The specimen was heated by pas sing an electrical current through the sample. The sample consists of a car bon strip as a heater and a Fe-Al alloy powder pressed onto its surface. A Pt-13% Ph thermocouple was used for temperature determination. In order to prevent oxidation of the specimen, the experiments were carried out in an a rgon-hydrogen flow. The spectra were analyzed and unit cell parameters at d ifferent temperatures were calculated using the General Structural Analysis System (GSAS) program. The phase transformation from bcc to fee 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.