Engineering topics

Bayuzick, R. J.

Publications and source records attributed to Bayuzick, R. J..

26 records · Page 2

NASA NTRS1986

Microstructures of niobium-germanium alloys processed in inert gas in the 100 meter drop tube

The 100 meter drop tube at NASA's Marshall Space Flight Center has been used for a series of experiments with niobium-germanium alloys. These experiments were conducted with electromagnetic levitation melting in a 200 torr helium environment. Liquid alloys experienced large degrees of undercooling prior to solidification in the drop tube. Several interesting metastable structures were observed. However, the recalescence event prevented extended solid solubility of germanium in the A-15 beta phase. Liquids of eutectic composition were found to undercool in the presence of solid alpha and solid Nb5Ge3.

Bayuzick, R. J.↗

NASA NTRS1986

Solidification of Nb-Ge alloys in long drop tubes

The 30-m and 100 m-long drop tubes at the Marshall Space Flight Center have been used to obtain large undercooling in Nb-Ge alloys. Electron beam melting has been used to obtain drops approximately 2.5 mm in diam. In the 30-m tube, many specimens fell the length of the tube without solidifying, and were ultimately liquid-quenched in oil. The amount of undercooling prior to the quench was usually around 0.13 T(m). In the 100-m tube, freezing generally initiated during free fall, and the maximum undercooling was around 0.22 T(m). Microstructures were characterized by a combination of X-ray diffraction, optical microscopy, and scanning electron microscopy with energy dispersive analysis by X-rays. A variety of interesting microstructures was observed.

Bayuzick, R. J.↗

NASA NTRS1985

Effect of Undercooling in a Low-Gravity Containerless Environment on the Structure and Properties of Alloys

The 30 meter and 100 meter drop tubes at the Marshall Space Flight Center offer a unique opportunity to study solidification in a containerless, microgravity environment. Samples are melted in a furnace at the top of the drop tube and solidify during a 4.5 second free fall in the 100 meter drop tube or a 2.6 second free fall in the 30 meter drop tube. The cooling rate obtained in the drop tubes is lower than cooling rates in atomization and splat-quenching processes. Decoupling the rapid solidification process allows the study of the effects of undercooling and recalescence on alloy morphologies. The research therefore has a three-fold purpose. The first is examination of the limits of undercooling of niobium and niobium-base alloys in the drop tube. The second purpose is the observation of microstructures resulting from the solidification of samples at large undercoolings and moderate cooling rates. The third purpose is the observation of metastable phase formation in highly undercooled samples.

Bayuzick, R. J.↗

NASA NTRS1985

Undercooling of niobium-germanium alloys in a 100 meter drop tube

The undercoolings of pure Nb and Nb-Ge alloys are examined using the 100-m drop tube of the Marshall Space Flight Center. The temperatures of the samples prior to release were measured, and IR detectors were utilized to monitor recalescence from solidification. It is observed that the Nb and Nb-Ge samples undercooled to the homogeneous nucleation limit. The data reveal that all the samples displayed a dendritic primary phase, except for alloys nucleating in the beta-phase field, which had a cellular phase. The composition of these phases are studied using EDXA; it is detected that the composition of the phases corresponds to the Jorda (1978) phase diagram.

Hofmeister, W. H.↗

NASA NTRS1984

Microgravity containerless processing in long drop tubes

Extensive experience in utilizing long drop tubes for studying effects of microgravity on the solidification of alloys was obtained. While some modifications are necessary to improve versatility, the facility proved to be most useful. Both an electron beam furnace and an electromagnetic levitation furnace can be used. The electron beam furnace is used with vacuum environments (0.00001 torr), whereas the levitation furnace is presently used only in inert gas environments (above 100 torr). Experiments are best applied to refractory alloys because of the sensitivity of the detectors now being used to observe solidification. Processing of lower melting point metals and alloys simply cannot be recorded. On the other hand, expected improvements in detector sensitivity will allow experimentation with relatively low melting alloys. In such cases, solidification will occur in flight only if higher inert gas pressure is used (100 to 760 torr) to increase heat loss by convection. Under these conditions microgravity conditions no longer apply. However, as shown by results to date, it is not microgravity as such that is important in drop tube solidification. Instead it is the containerless nature of the process that is significant, leading to large degrees of undercooling before solidification and therefore to unique alloys.

Bayuzick, R. J.↗

NASA NTRS1984

A review of long drop tubes as a supplement/alternative to space experiments

A description of the 100-m drop tube at the Marshall Space Flight Center is presented, along with some undercooling observations and a discussion of some microstructural properties of deeply undercooled Nb-Ge alloys. The facility comprises two turbopumps which can evacuate the tube to 0.00001 torr, and three IR detectors at 15, 80, and 103-m levels which are sensitive to light in the range of 9660-2635 K (wavelength range of 0.2 to 1.1 microns), though recalescence events were detected at 1700 K. Finally, hypercooling regimes and maximum possible undercooling in vacuum are defined for several materials, including Al, Cu, Ni, Fe, Pt, and Nb.

Bayuzick, R. J.↗

NASA NTRS1982

Containerless processing of Nb-Ge alloys in a long drop tube

The thirty-two meter drop tube at the Marshall Space Flight Center was used to study the effect of zero gravity containerless processing on the structure and properties of materials. The concept involves the suppression of heterogeneous nucleation of solid in liquid and, therefore, solidification accompanied by large degrees of undercooling. Under these conditions metastable phases can be formed or, at the very least, unique nonequilibrium microstructures (containing equilibrium phases) with unique properties can be produced. The drop tube solidification was applied to niobium base alloys with emphasis on the Nb-Ge binary system in an effort to produce metastable phases with high superconducting transition temperatures in bulk specimens. In the past, only lower Ge alloys (Nb-13 a/o, Nb-18 a/o, and Nb-22 a/o) could be undercooled. Higher Ge alloys (e.g., Nb-25 a/o Ge and Nb-27 a/o Ge) can now be undercooled on a routine basis.

Bayuzick, R. J.↗

NASA NTRS1982

Solidification studies of Nb-Ge alloys at large degrees of supercooling

A 32 meter evacuated drop tube has been used to investigate the solidification of Nb-Ge alloys after deep undercooling. Samples have been supercooled as much as 500 K below the liquidus by using free-fall conditions to eliminate crucible induced nucleation. Final microstructures are dependent on the quenching rates at the bottom of the drop tube with a striking extension of the beta phase solubility limit at the higher quenching rates.

Lacy, L. L.↗