Phase Transformation Of Beta-Fesi2-Based Alloys Under In-Situ High-Temperature And High-Pressure X-Ray Diffraction Measurements

The dynamic behaviour of phase transformation in beta-FeSi2 based thermoelectric materials Fe1-xMxSi2+y (M = Mn or Co) has been studied by using differential scanning calometry (DSC) and in situ high-temperature and high-pressure X-ray powder diffraction measurements (EDXRD) using synchrotron radiation. The investigated materials were powders prepared by rapid solidification (melt spinning). It's found by DSC and EDXRD that the alpha + epsilon eutectic structures in the rapidly solidified alloys transform to beta phase (alpha-Fe2Si5 + epsilon-FeSi -> beta-FeSi2) in a lower temperature range below 700 degrees C. The formed P phase decomposes reversely to alpha and epsilon phase in a higher temperature range above 950 degrees C. The transformation temperatures T-1 (alpha + epsilon -> beta) is greatly influenced by the heating rate. By EDXRD measurements, it is found that high pressures have a great influence on the phase transformation temperature T-1 and T-2 (beta -> alpha + epsilon). Different doping elements (Mn, Co, or Al) have also great influence on the phase transformation temperature. EDXRD has simulated the process of hot uniaxial pressing.