No abstract

High‐density specimens were plastically deformed under four‐point transverse bending. Tests were conducted in vacuum in the region 1400° to 1700°C under stresses of 1000 to 4500 psi. The activation energy for creep was 99.0 kcal/mole. Creep rate was directly proportional to the applied stress and inversely proportional to the square of the grain diameter. The deformation behavior is ascribed to a Nabarro‐Herring type mechanism. Results show that creep was the same in tension and compression.

both sides of the disks revealed that the grains were misoriented by < l o o . The disks in Fig. 3 are oriented so that the (1130) planes are almost parallel to the faces of the disks. Dislocation densities on the (0001) plane were determined in the interior of the wedge-shaped grains after the specimens were etched with hot orthophosphoric acid.' Dislocation densities of l X I O s cm-' were obtained. These are comparable to those of sapphire grown by the Czochralski technique>-* The absorption edges of a sapphire disk 0.9 cm thick were determined with three spectrophotometers. 4: The disk was essentially transparent to radiation from 0.25 pm in the uv to 4.5 pm in the ir, in agreement with results of other investigators.!' Society-Discussions and Notes529 Fig. 3. Sapphire disks grown by gradient furnace technique. Disk at left is as removed from crucible; disk at right was ground and polished to a submicron finish and a portion removed for other studies.':'Model 202 ultraviolet-visible spectrophotometer, Perkin-Elmer Corp., Norwalk, Conn., and Models IR-12 and DK-1A spectrophotometers, Beckman Instruments, Inc., Fullerton, Calif.

The uranium-niobium-zirconium ternary system exhibits a series of solid solutions at high temperature. Addition of both niobium and zirconium stabilizes the body-centered-cubic gamma phase to a lower temperature.A study has been made of one particular ternary alloy, the U-7.5 w/o Nb-2.5 w/o Zr composition. The relationship of transformation characteristics of the alloy to its physical and mechanical properties has been determined. This weldable alloy is concluded to be an excellent material for engineering applications. Tensile yield strengths of 100,000 to 200,000 psi are obtainable, with elongations of 12% to 4%, respectively, depending on heat treatment.