Atom Probe Tomography of Cold Sprayed and Laser Assisted Cold Sprayed Fe-Ni-Zr ODS Steel

In this work the distribution of nano-scale oxide precipitates in a Fe-Ni-Zr oxide dispersion strengthened (ODS) steel deposited using cold spray (CS) is laser assisted cold spray (LACS) is reported. In conventional CS a substrate temperature of 320°C was measured throughout the process, and with LACS a substrate temperature of 950°C was maintained throughout the process. In order to determine if precipitates were preserved or altered during the deposition process, atom probe tomography was used.

Samples were first prepared using standard metallographic techniques followed by vibratory polishing. Needles were lifted out using a FEI Quanta 3D FEG Dual Beam and sharpened with a Tescan LYRA3 FIB FESEM into atom probe samples. Samples were run in a Cameca Local Electrode Atom Probe 5000 XS.

The raw data before analysis is given by the files "APT-CS320-RAW.rhit" and APT-LACS950-RAW.rhit". In order to construct compositional maps and quantify the size and spacing of oxide dispersants, the data was analyzed using Integraded Visualization and Analysis Software version 3.8. The analyzed data is given in "APT-CS320-analyzed.xlsx" and "APT-LACS950-analyzed.xlsx." Specific details necessary to follow these procedures can be found in work by Welsh et al [1] and Guo et al [2].

Oxide dispersants are visualized by 1 at. % and 5 at. % Zr isosurfaces using isosurface selection techniques patterned off of the inflection point determination work of Hornbuckle et al [3]. A stoichiometry of approximately 40% Zr to 60% O was found within the isosurfaces. The Zr and O compositions are not exactly stoichiometric for ZrO2 due to complicated field-evaporation effects.

The ZrO2 dispersants are found to have a number density of 4.30x10^23 m^-3 with a spacing of 17.2 nm for the CS deposit and 2.49x10^23 m^-3 with a spacing of 22.8 nm for the LACS deposit. Oxide dispersants are preserved in the deposition process in both cases, but laser heating of the substrate causes coarsening of the dispersants.

References:
[1] http://dx.doi.org/10.1155/2016/4597271
[2] https://doi.org/10.1016/j.actamat.2017.04.036
[3] https://doi.org/10.1016/j.ultramic.2015.03.003