Non-equilibrium intragrain concentration redistribution of the alloying elements in austenitic steels under irradiation

Radiation-induced and thermally activated decomposition of austenitic 16Cr1 5Ni3Mo1Ti, 32Ni, 34Ni steels at high temperature (500-650 degrees C) were e xamined. High doses (up to 10-200 dpa) in 16Cr15Ni3Mo1Ti stainless steel wi th 1.5 MeV Kr ions and 450 keV Fe ions at 550-650 degrees C lead to the app earance of relatively large regions (up to 200-400 nm) of concentration-osc illations with 'mosaic' dark-white diffraction contrast in TEM images. The radiation-induced redistribution of alloying elements takes place thanks to inverse Kirkendall effect and, in particular, removal of Cr to cell volume from boundaries of coarse cellular structure. The competing formation of u ltrafine subgrains and grains 10-50 nm in size structure in Ti-free steel ( 16Cr15Ni3Mo) impedes the development of large ingrain segregations. The Mos sbauer investigations showed that the 32Ni and 34Ni steels with purposefull y produced concentration-oscillations were fully homogenised in that high-t emperature region. This fact indicated the absence of the thermal decomposi tion dome in the Fe-Ni equilibrium diagram. (C) 2000 Elsevier Science B.V. All rights reserved.