Abstract
Knowledge on the chemical state of phosphorus (P) segregated at grain boundaries in iron is important in discussing the mechanism of grain boundary decohesion by P. In order to determine the chemical state of P at grain boundaries, X-ray photo-electron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used.
Fe-P alloy specimens with the P concentration between 0.05mass% and 15.6mass% was fractured in the analyzer chamber of which vacuum was better than 5×10-9Pa(4×10-11torr). Since the amount of P segregated at grain boundaries is small, XPS had to be measured for a long time to accumulate the signal from P. The prolonged measurement was possible without contamination by the residual gas because of the high vacuum. XPS of the segregated P was found to be identical to XPS of P in Fe3P. This result supports the Losch model for the grain boundary decohesion by P, in which a segregated P atom forms a strong bond with surrounding Fe atoms and reduces the strength of bond between Fe atoms neighboring to the P atom.
The shape of Auger electron spectrum of P in solid solution varies with the P concentration, but that of the segregated P is independent of the P concentration and identical to that of P in Fe3P. The importance of the variation of the shape of Auger electron spectrum with the P concentration in the quantitative analysis of the segregated P is discussed.
