FINAL REPORT ON MISCIBILITY GAPS IN Nb-U AND Nb-U-Zr SYSTEMS Page: 8 of 99
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1I. EXAMINATION OF ALOYS.
(a) Metallographic Technique,
Specimens were mounted in bakelite, wet ground to 600
paper, and polished with 0-1 A diamond dust and slow cutting
alumina, For high U alloys the most generally useful etch was
10% aqueous oxalic acid, used electrolytically at 3-6 volts.
For Nb-rich alloys a polish-attack method was used with slow
cutting alumina and solutions of nitric and hydrofluoric acids
in various proportions.
(b) X-ray Technique.
All X-ray photographs were obtained from the block
metallographic specimens, using a 14 cm diameter camera in
which the specimen is oscillated and rotated with respect to
a beam of filtered Co K a X-radiation. The majority of the
binary alloys and the more important ternary compositions
(a) The Miscibility Gap in the U-Nb system.
The U-'b miscibility gap, drawn in accordance with present
metallographic and X-ray results, is presented in Fig. 9. The
monotectoid is placed at 17.5 a/o Nb and 61+0oC, and the gap -
extends at 6400C to -v 65 a/o Nb. The procedure used in establishing
the gap was to decompose the alloys at low temperatures (640 - 6600C),
and to locate the phase boundaries by observing the phase changes
produced on reheating to higher temperatures-. This approach avoids
the difficulty of the sluggish y1 + Y2 decomposition from y at
temperatures above 70000, as reported by P.C.L. Pfeil . The structures
encountered in the various phase fields are described in turn below.
1. The y field.
In alloys with less than 20 a/c Nb, the stable y phase could
not be retained on quenching to room temperature. Alloys containing
up to 17.5 a/o Nb transformed on quenching either to the a,' or ,"
modifications of a, and some distortion of the b.c.c. pattern was
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FINAL REPORT ON MISCIBILITY GAPS IN Nb-U AND Nb-U-Zr SYSTEMS, report, January 1, 1959; United States. (digital.library.unt.edu/ark:/67531/metadc877724/m1/8/: accessed June 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.