SEDL / STP / STP1023-EB / STP18882S

Intermetallic Precipitates in Zirconium-Niobium Alloys

Meng, X
Ph.D. student and professor and department head, University of Windsor, Windsor, Ontario

Northwood, DO
Ph.D. student and professor and department head, University of Windsor, Windsor, Ontario

Pages: 9    Published: Jan 1989

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Abstract

Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS) have Seen used to study the composition and structure of intermetallic precipitates, principally those containing iron and chromium, in Zr-2.5wt%Nb pressure tubing and Zr-lwt%Nb fuel sheathing. The Zr-lwt%Nb fuel sheathing contained Zr(FeCr)² Laves phase precipitates with either the C-14 hexagonal or C-15 cubic structure. Orthorhombic Zr³Fe precipitates were also tentatively identified. Tetragonal Zr²Fe precipitates were found in Zr-2.5wt%Nb pressure tubing containing 700-ppm iron. The volume fraction of Zr²Fe was very small (<0.1% on an area basis) and was much smaller than the volume fraction of Zr(FeCr)² precipitates in Zr-1wt%Nb.

The difference in type and volume fraction of iron-containing precipitates in Zr-lwt%Nb and Zr-2.5wt%Nb despite similar iron and chromium contents is tentatively attributed to the different volume fractions of the β-phase. Iron is a β-stabilizer and concentrates in the β-phase. The Zr-2.5wt%Nb alloy, which contains the higher volume fraction of β-phase, takes in more iron in solution in the β-phase thus leaving less to precipitate out as an intermetallic.