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Tungsten and Dispersion-strengthened Tungsten Made by Freeze Drying.
Ferrante-MJ; Lowery-RR; Robidart-GB
NTIS: PB 198 267 :32 pages
The Bureau of Mines investigated the applicability of the freeze- drying technique for preparing dispersion-strengthened tungsten powders suitable for conversion by powder metallurgy into materials which might have improved high-temperature strength. Extruded rods from compacts of tungsten-5 volume percent thoria had at 1,650 deg c a tensile strength of 30,300 psi and a 10-hour stress-rupture strength of 12,700 psi. These are slightly below those measured for swaged rods of commercial tungsten-3.7 Volume percent thoria. Only those tungsten-thoria dispersions containing a stoichiometric deficiency of oxygen yielded a significant strengthening effect. A low-melting eutectic formed in extruded tungsten dispersions containing either zirconia or yttria, which caused a lowering of the tensile strengths. These tensile strengths were only slightly higher than strengths of elemental tungsten made from commercial powder having a particle size of 2.4 Microns (fisher subsieve). Sheet made from this commercial tungsten had a slightly higher tensile strength than tungsten made by freeze drying, but the freeze- dried tungsten sheet had a lower recrystallization temperature, a lower ductile-to-brittle transition temperature, and a higher purity.
IH; Report of Investigation;
NTIS Accession No.
NTIS: PB 198 267