EELS analysis of complex precipitates in PM 2000 steel

Institute for Materials Research I, Forschungszentrum Karlsruhe GmbH, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

Corresponding author: michael.klimenkov@imf.fzk.de

Received: 9 November 2005
Revised: 19 June 2007
Accepted: 22 February 2008
Published online: 4 June 2008

Abstract

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 Y₃Al₅O₁₂ (garnet) and YAlO₃ (perovskite) as well as -Al₂O₃ and -Al₂O₃ precipitates can be distinguished by analysing the O-K energy loss near-edge structure (ELNES). The formation of interface-specific phases on Al₂O₃/YAlO₃, Al₂O₃/matrix and Y₃Al₅O₁₂/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 Al₂O₃ 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.