EELS analysis of complex precipitates in PM 2000 steel

Formation of different types of nanosized Al-containing oxide precipitates in an Fe-Cr-Al alloy (PM 2000) was studied by electron energy loss spectroscopy (EELS) using a transmission electron microscope (TEM). It was shown that Y(3)Al(5)O(12) (garnet) and YAlO(3) (perovskite) as well as gamma-Al(2)O(3) and alpha-Al(2)O(3) precipitates can be distinguished by analysing the O-K energy loss near-edge structure (ELNES). The formation of interface-specific phases on Al(2)O(3)/YAlO(3), Al(2)O(3)/matrix and Y(3)Al(5)O(12)/matrix interfaces was also investigated by specially resolved EELS analysis. Applicability and sensitivity of the EELS method in the study of steel precipitates were discussed. A sharp pre-peak or "pre-shoulder" in the O-K edge was observed and studied by means of spatially resolved EELS of oxide inclusions. The intense pre-peak was found to be caused by radiation damage induced by the electron beam of the Al hydroxide phase inside Al(2)O(3) inclusions. This phase formed due to the incorporation of hydrogen in the matrix during mechanical alloying in the hydrogen atmosphere. The "pre-shoulder" of the main O-K feature measured on the inclusion/matrix interface results from the formation of a thin Ti-O layer.