COMPOSITION OF PHASE-DECOMPOSITION PRODUCTS IN FE-28CR-5NI ALLOY DETERMINED BY MOSSBAUER-SPECTROSCOPY

The effect of Ni on the internal magnetic field and the isomer shift of Fe-57 in Fe-Cr alloys containing 3 to 14 at % Cr and 70 to 90 at % Cr were examined at room temperature by Mossbauer spectroscopy. A model Fe-28%Cr-5%Ni alloy was aged up to 5000 h at 723 K to investigate the phase decomposition of ferrite in a commercial duplex stainless steel. The alloy finally decomposed into a Cr-rich phase (alpha') and an Fe-rich phase (alpha) after aging. A paramagnetic absorption peak due to the alpha' phase has an isomer shift of -0.110 mm/s at room temperature. The value corresponds to a Cr content of 85(+/-1)at%Cr. The composition of the alpha phase was estimated to be 11(+/-1)at%Cr from the average internal magnetic field and the internal field distribution curve. The result of alpha phase was consistent with a result obtained by atom probe microanalysis. The latter underestimated the Cr content of the alpha' phase in comparison with the Mossbauer effect.