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An experimental study was conducted to determine the acceptable combinations of process variables for the production of a niobium-titanium superconducting alloy in a pure aluminum matrix by hydrostatic extrusion. Conditions for sound flow and defective flow are shown on plots of percent reduction in area versus die semicone angle. The superconductor used was a 56 percent Nb-44 percent Ti alloy surrounded by a matrix of 99.995 percent pure aluminum. The study was performed in three phases. Single-core billets were extruded into atmospheric pressure with reduction in area, die semicone angle, and the ratio of the volumes of the two phases being varied. Single-core billets were extruded into receiver pressure with reduction in area and die semicone angle being varied. Billets with three cores were extruded with reduction in area, die semicone angle, friction, and receiver pressure being varied. In all cases there was a light mechanical bond between the two materials produced by interference fitting of the cores into drilled holes. Experimental results showed that increasing the receiver pressure increases the range of acceptable process variables to produce sound flow. Although it was possible to produce sound flow, the results were not always consistent and repeatable. This is largely due to the great difference in strength between the soft aluminum and the hard superconductor and the difficulty in accurately controlling the bond strength. It is expected that the beneficial effect of receiver pressure will be even more pronounced with a tighter control on bonding.

The elastic moduli of pressure-sintered nickel oxide near theoretical density have been measured by three different techniques. The values of Young's modulus and the shear modulus at room temperature determined by the resonant sphere method were 9.58 X 10 • dynes/cm •' and 3.38 X 10 xx dynes/cm •', respectively. The value of Young's modulus determined by a three-part composite oscillator technique was 9.56 X 10 x• dynes/cm •', in good agreement with the resonant sphere measurements. Measurements of Young's modulus and shear modulus by the pulse-transmission method were subject to fairly large end effects, which gave lower values. The temperature of the anomalous increase in Young's modulus and in relative acoustic loss was found to be 250øC 4-1/2øC, in excellent agreement with previously reported measurements for the N6el temperature of nickel oxide. 1968]. This is attributable to their abundance in the earth's upper crust, their resultant geophysical interest, and the relative ease of manufacture of well characterized materials near theoretical density under laboratory conditions [Spriggs et al., 1963]. However, recent geophysical interest in the density-versus-depth behavior of the inner structure of the earth [Press, 1968] demonstrates the need for accurate modulus measurements of heavy metal oxides, particularly those of the first transition series. The elastic moduli of pressure-sintered a-Fe•.O,, as a function of pressure, have recently been determined by Liebermann and Schreiber [1968]. The purpose of this paper is to report the room-temperature elastic moduli and the variation of Young's modulus with temperature for high-density pressure-sintered nickel oxide. EXPERIMENTAL PROCEDURE AND RESULTS Sample preparation. The specimens used for this investigation were prepared from Johnson-Matthey Co. 99.999% pure nickel oxide powder ('Specpure ' grade I, Ag • 1, A1 •( 1, Ca •( 1, Cu •( 1, Fe •( 10, Mg •( 1, and Si • 3 ppm, respectively, with total cation impurities lessCopyright (• 1971 by the American Geophysical Union. than 10 ppm). Transmission electron microscope evaluation showed the powder to have a very narrow particle size distribution ranging from 2 to 5 t•m. Pressure sintering of the nickel oxide was performed at approximately 0.1 mtorr ambient pressure in a Vacuum Industries Model 1-2300 vacuum pressure-sintering furnace. The samples were sintered in TZM (Climax Molybdenum Co., Coldwater, Mich. Mo-0.5% Ti-0.08% Zr wrought alloy) supported, high-purity alumina dies [Moss and Stollar, 1966] at an applied pressure of 8.8 X 106 kg/m •-and at a temperature of 1100øC for 90 minutes. The pressure was reduced and the sample was then furnace-cooled. The alumina die insert was then cut apart with a diamond saw