AN INTERNAL FRICTION STUDY OF THE MECHANISM OF IMPROVEMENT OF THE PROPERTIES OF Fe-Cr-Al ALLOYS BY THE ADDITION OF A SMALL AMOUNT OF RARE EARTH ELEMENTS

Abstract
Three types of specimens of Fe-Cr-Al alloys containing a small amount of rare earth elements were used in this work. Several internal friction peaks were observed at high temperature in each specimen. (1) For specimen 1, Cr₁₃Al₆Mo₂ (with 0.05 wt% Ce) internal friction peaks occurred at temperatures around 450°C, 624°C and 690°C with frequencies of vibration of 0.67Hz, 0.59Hz and 0.55Hz respectively. The activation energies of the last two peaks were found to be about 3.3ev and 4.0ev. (2) For specimen 2, Cr₂₇Al₇Mo₂ (with 0.056 wt% Ce) still three internal friction peaks occurred at temperatures around 523°C, 663°C and 713°C with frequencies of vibration of 0.61Hz, 0.56Hz and 0.52Hz respectively. The activation energies of the last two peaks were found to be about 3.6ev, 4.0ev. (3) For specimen 4, Cr₂₃Al₆ (with 0.065 wt% Y) three internal friction peaks were also observed at temperatures around 529°C, 632°C and 690°C respectively. 3.1ev and 3.9ev are the activation energies related to the last two peaks. It is suggested that the first peak is Zener relaxation peak to be associated with the stress induced reorientation of Fe-Cr atomic pairs. The other two peaks are the solute grain boundary peaks of Fe-Cr and Fe-Re. Based on the results mentioned above, the mechanism of improvement of the high temperature properties of Fe-Cr-Al alloys by the addition of a small amount of rare earth elements was discussed.