Description: From abstract: "Transformation kinetics of binary U -Nb and ternary U-Nb-base alloys were investigated. Additions included zirconium, chromium, titanium, silicon, nickel, nnthenium, and vanadium. Encapsulated samples were given a homogenizstion anneal at 1000 or 1100/sup o/C, water-quenched from 906/sup o/C to retain the phase, and reheated to temperatures between 360 and 600/sup o/C. The metastability of the phase was examined by metallographic, hardness, resistometric, dilatometric and x-ray-diffraction techniques. The U -Nb system is characterized by a monotectoid decomposition of the high temperature allotrope at about 645/sup o/C to form alpha and ₂, a niobium-rich cubic structure. Decomposition in U-Nb and in most U-Nb-X alloys occurred by a continuous precipithtion of alpha from the body-centered cubic phase with a resultant enrichment in niobium of until the equilibrium ₂ composition was reached. In the U-Nb-Ti and U-Nb-V systems, alpha and /sub 2/ were coprecipitated. Annealing at 550 and 600/sup o/C produced decomposition products which, in most materials, originated at the grain boundaries; a fine precipitate which initiated throughout the matrix was observed at lower annealing temperatures. Increasing the niobium content resulted in greatly increased stability. The following elements added to a U-Nb base were found to retard transformation of the phase: zirconium, chromium, ruthenium, and vanadium. Additions of titanium, silicon, and nickel produced alloys which were less stable than the U-Nb base to which they were added. Cold-working a U-7 wt. % Nb-2 wt. % Zr composition caused a more rapid transformation upon annealing at 360 and 450/ sup o/C, and the resulting microstructures were different. Continuous cooling transformation studies were conducted on U-10 wt. % Nb materials, solution annealed at 700 and 950°C, and cooled at various linear rates to temperatures between 300 and 600/sup o/C. Cooling rates between 8.5 and 14.5/sup o/C per minute were required to prevent transformation of ...
Creator: Parry, Sidney J. S.; Holtz, F. C. & Van Thyne, R. J.
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