Deformation-induced nonequilibrium grain-boundary phase in submicrocrystalline iron

The shapes of Mossbauer spectra of coarse-grained annealed armco iron and s ubmicrocrystalline (SMC) iron with a grain size of 0.22 mu m were compared. The SMC was made from the armco iron by pressure shear and subsequent anne aling at 420 degrees C. We intended to separate an additional subspectrum, which appears as a result of the grain refinement. That subspectrum was att ributed to grain-boundary atoms or the "grain-boundary phase" (GBP). The vo lume fraction of that phase was determined. On the average, the GBP interat omic spacing was suggested to be 1% larger than that of the grain phase (GP ) and the presence of considerable compressive stresses in the GBP were ded uced. A possible reason for the satellite subspectrum appearing after the g rain refinement was that it was attributed to a sudden change in the fundam ental characteristics of the solid at a certain critical Value of the latti ce parameter, which varies continuously in going from the geometrical bound ary to the grain center. (C) 2000 Acta Metallurgica Inc.