ATOM PROBE FIELD-ION MICROSCOPY STUDY OF AGING BEHAVIOR OF A MODEL FE-NI-CO-MO MARAGING-STEEL

This paper reports an atom probe field-ion microscopy (APFIM) study of the ageing reactions in a model Fe-18.2%Ni-8.8%Co-2.9%Mo (at. %) maraging steel, using both the conventional APFIM and the position-sensitive atom probe (POSAP). Two different families of intermetallic phases (omega-phase and Fe7Mo6) have been found to contribute to age-hardening. The composition and morphology of these precipitates were studied in the alloy aged at 414-degrees-C and 510-degrees-C. No evidence was found for the existence of Mo-rich clusters in the as-quenched alloy. The APFIM results are compared with studies by Servant et al. using other techniques, and previous studies on a commercial Ti-containing steel by the authors.