SEGREGATION AT SPECIAL GRAIN BOUNDARIES IN Fe-Si ALLOY BICRYSTALS

The segre ation of silicon to the C=3, 112) and C=S, (013) symmetrical grain boundaries 1 was studied in well-fefined bicrystals of an Fe-l .9 at%Si alloy annealed in the range 773 1173 K using Auger electron spectroscopy. The segregation enthal y, AI1 = -8.1 * 0.5 kJ/mol, and entropy, AS = -69 r 0.4 i/(mol K), were determined for the (013f grain boundary in the temperature range 973 1173 K. For the (112) boundary the corresponding values AH = -4 * 3 kJ/nlol and AS = -4 * 3 J/(mol K) were obtained. At both these boundaries, a decrease of the segregation of Si was observed at 773 K. In addition, a wide in-depth distribution of silicon enrichment was observed away from the boundaries in spite of relatively high annealing temperatures and times. Both effects are probably due to the ordering effects in this alloy. Addition of phosphorus to this alloy caused a depletion of silicon at the (112) grain boundary.