Mössbauer Effect Studies of Spinodal Decomposition in Fe-Cr
Mössbauer effect studies have been carried out to investigate the 475°C decomposition of binary Fe-Cr alloys. Homogenized and quenched alloys of compositions Fe-24, 30, 37, 44, and 60 at. %Cr gave complex spectra at room temperature. Satisfactory fitting of the data was obtained by assuming random atomic arrangement and Mössbauer parameters obtained from dilute Fe-Cr alloys. These fits indicate that the fractional change of the iron hyperfine field due to an additional chromium nearest or next-nearest neighbor remains virtually constant over this wide composition range. The effect of more distant neighbors is evidenced by the required assumption of linewidths somewhat larger than natural.
When the Fe-60 at. %Cr alloy was aged at 475°C for up to 30 hr, the spectrum broadened by about 20% but showed no signs of resonant absorption at energies expected for the equilibrium two-phase alloy. This indicates that initial decomposition produces regions of composition not very much different from the average composition. Affter 80 hr of aging, new structure appeared in the spectrum and became stronger with subsequent aging. The results of spectra measured at 200°C and room temperature are consistent with expectations for spinodal decomposition.
KeywordsHyperfine Field Spinodal Decomposition Chromium Alloy M6ssbauer Spectrum Mossbauer Spectrum
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