Methods of quantitative matrix analysis of Zircaloy-2

The zirconium-based alloy Zircaloy-2 contains small amounts of iron, chromium and nickel dissolved in the matrix. Several attempts to measure these amounts have been made in the past, but the results are conflicting and inconclusive. The advent of wide angle, laser pulsed atom probe tomography motivates a new attempt to analyze the matrix. Large datasets are now easily obtained using laser pulsing but quantification is not straightforward due to rather complex mass spectra. Zircaloy-2 contains about 1 wt% tin, 0.1 wt% oxygen and trace amounts of Si, C and Al. Severe overlaps make quantification of any Fe+, Cr+ and Ni+ ions impossible. Quantification of Fe, Cr and Ni therefore requires that they appear as doubly charged ions only, and consequently the field must be kept high enough. In addition, adsorbed CO+ may appear at the main peak of Fe2+. In the paper a method is reported, which gives what we believe an accurate quantitative analysis of at least iron and chromium in the matrix.

Research highlights
► APT of the matrix of Zircaloy-2 using laser pulsing.
► Quantification of Fe, Cr and Ni requires the evaporation field to be high enough.
► The water quenched matrix contained 22 wtppm Fe and 49 wtppm Cr.
► The furnace cooled matrix contained 6 wtppm Fe and 11 wtppm Cr.