Am phases in the matrix of a U–Pu–Zr alloy with Np, Am, and rare-earth elements

•Documents nanocrystalline two-phase microstructure in matrix of U–Pu–Zr–Np–Am–RE alloy.•Matrix phases generally consistent with U–Pu–Zr phase diagrams.•Both matrix phases contain U, Np, Pu, and Am.•Includes single-phase microanalysis and diffraction data. Phases and microstructures in the matrix of an as-cast U–Pu–Zr alloy with 3wt% Am, 2% Np, and 8% rare-earth elements were characterized by scanning and transmission electron microscopy. The matrix consists primarily of two phases, both of which contain Am: ζ-(U, Np, Pu, Am) (∼70at.% U, 5% Np, 14% Pu, 1% Am, and 10% Zr) and δ-(U, Np, Pu, Am)Zr2 (∼25% U, 2% Np, 10–15% Pu, 1–2% Am, and 55–60at.% Zr). These phases are similar to those in U–Pu–Zr alloys, although the Zr content in ζ-(U, Np, Pu, Am) is higher than that in ζ-(U, Pu) and the Zr content in δ-(U, Np, Pu, Am)Zr2 is lower than that in δ-UZr2. Nanocrystalline actinide oxides with structures similar to UO2 occurred in some areas, but may have formed by reactions with the atmosphere during sample handling. Planar features consisting of a central zone of ζ-(U, Np, Pu, Am) bracketed by zones of δ-(U, Np, Pu, Am)Zr2 bound irregular polygons ranging in size from a few micrometers to a few tens of micrometers across. The rest of the matrix consists of elongated domains of ζ-(U, Np, Pu, Am) and δ-(U, Np, Pu, Am)Zr2. Each of these domains is a few tens of nanometers across and a few hundred nanometers long. The domains display strong preferred orientations involving areas a few hundred nanometers to a few micrometers across.