ANALYSIS OF NANOMETER-SIZED PRECIPITATES USING ATOM PROBE TECHNIQUES

Positive-sensitive detection has been combined with time-of-flight mass spectrometry in the atom probe field-ion microscope to yield a system in which both chemical identity and spatial information are obtained for individual ions field evaporated from the specimen surface. This allows the variations in composition originally present in the sample to be reconstructed in three dimensions with subnanometer resolution. From these data, selected region analyses are easily performed, permitting the accurate determination of precipitate compositions without the difficulties of alignment that can plague conventional atom probe studies of very fine precipitates. The position-sensitive atom probe technique is described, together with some examples of its application in the study of precipitation in maraging steels, aluminium alloys, and the iron-copper system. © 1990.