A comparison of two high spatial resolution imaging techniques for determining carbide precipitate type and size in...

Two high spatial resolution imaging techniques, focused gallium ion beam imaging in conjunction with XeF₂ gas (FIB/XeF₂) and high-speed atomic force microscopy (HS-AFM), were used to analyse 9Cr-1Mo ferritic steel samples, which had been exposed for extended periods to hot CO₂ gas containing traces of CO, H₂, H₂O and CH₄. The carbide precipitates embedded in the metal matrix were observed and their morphology, size and spatial distribution were quantified using these two techniques. The lower resolution of the FIB/XeF₂ imaging technique suggested that small carbide precipitates (<50 nm) may be missed, while the existence of a limited flow layer introduced by sample preparation may influence the HS-AFM results. The gallium ion beam was used to remove a thin oxide layer of approximately 50 nm from sample surfaces prior to FIB/XeF₂ imaging, avoiding the influence of surface contamination. HS-AFM provided higher resolution (∼5 nm) than FIB/XeF₂ imaging. A quantitative comparison of the experimental data confirmed the value of both FIB/XeF₂ and HS-AFM for imaging carbide precipitates, while clarifying their strengths and limitations.