Quantitative atom probe analysis of carbides

Abstract

Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti(2)AlC grains in different materials as well as on large M(23)C(6) precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the (13)C isotope, and calculating the concentration of (12)C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) and Ti(2)AlC an additional difficulty arises from the overlap between C(2)(+), C(4)(2+) and Ti(2+) at the mass-to-charge 24 Da.

Contribution of core-loss fine structures to the characterization of ion irradiation damages in the nanolaminated ceramic Ti3AlC2

“…On the other hand, we have previously shown that the agreement between experiment and calculation is satisfactory at the C K edge, for which the octahedral site leads to an overall more isotropic chemical bonding and the Muffin-Tin approximation thus adapted. To end, let us mention that, like at the C K edge, we do not include any disorder in the FEFF calculation, disorder that is known to be significant: a corrugation of Al planes could also contribute to increase the disagreement in the case of the Al K edge [67,4].…”

Reduction of multiple hits in atom probe tomography

“…The detection efficiency is usually 30-60%, depending on instrument type, and it is the same for all elements, thus giving excellent compositional accuracy, without the need of standard samples and element specific calibration. In some cases, though, the accuracy of concentration measurements is significantly reduced, for example when analyzing carbides [1], nitrides [2], silicides [3] or semiconductors [4]. In the case of carbides, the main reason why the obtained carbon concentration is usually too low is the limited capability of the detector to register all ions resulting from the same pulse.…”

“…In some cases it is possible to use only isotopes of low abundance for quantification, as the probability is low that more than one such ion from a single pulse hit the detector. This has been demonstrated for the analysis of carbides, using the 13 C isotope [1]. To some extent it is possible to decrease the fraction of multiple events by changing the analysis conditions.…”

Effect of Ti on Evolution of Microstructure and Hardness of Martensitic Fe–C–Mn Steel during Tempering

“…The quantitative analysis is based on isotope distributions of different ions of relevant atom types. 24 The quantitative APT analysis of C atoms is based on ions detected at 6, 6.5, 12 and 13 Da, plus all ions which exceeded the expected Ti level at 24 Da (as two C ions).…”