A procedure is presented for systematically and reproducibly preparing alloy specimens for the study of grain boundary (GB) segregation employing both transmission electron (TEM) and atom-probe field-ion microscopies (APFIM) to examine the same GB; the procedure is illustrated for an Fe(Si) alloy. A commercially available oxygen plasma source is incorporated in the sample preparation procedure to remove all traces of hydrocarbon build-up introduced during TEM GB analysis, thus allowing controlled backpolishing after a TEM analysis. Specifications for the optimum tip geometry, i.e., how a GB is positioned in a tip via backpolishing to maximize the probability of its observation and subsequent compositional analysis via APFIM, are empirically determined: 30-200 nm for the GB-to-tip separation, and 40-80 nm for the GB diam for shank angles less than 20°. It is demonstrated that accurate quantitative APFIM analyses of an Fe-3 at. % Si alloy are possible for pulse fractions ≥15% and specimen temperatures ≤55 K. Results are presented for a ∑≊3a GB that was first analyzed via TEM to determine its five macroscopic degrees of freedom, and then analyzed via APFIM to measure an average GB segregation enhancement factor for Si of 3.51±0.34 at 823 K.
ASJC Scopus subject areas