Laves intermetallics in stainless steel–zirconium alloys

Laves intermetallics have a significant effect on properties of metal waste forms being developed at Argonne National Laboratory. These waste forms are stainless steel–zirconium alloys that will contain radioactive metal isotopes isolated from spent nuclear fuel by electrometallurgical treatment. The baseline waste form composition for stainless steel-clad fuels is stainless steel–15wt.%zirconium (SS–15Zr). This article presents results of neutron diffraction measurements, heat-treatment studies and mechanical testing on SS–15Zr alloys. The Laves intermetallics in these alloys, labeled Zr(Fe,Cr,Ni)2+x, have both C36 and C15 crystal structures. A fraction of these intermetallics transform into (Fe,Cr,Ni)23Zr6 during high-temperature annealing; we have proposed a mechanism for this transformation. The SS–15Zr alloys show virtually no elongation in uniaxial tension, but exhibit good strength and ductility in compression tests. This article also presents neutron diffraction and microstructural data for a stainless steel–42wt.%zirconium (SS–42Zr) alloy.