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Douglas, F. C.

Publications and source records attributed to Douglas, F. C..

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Application of diffusion barriers to high modulus fibers

Barrier layers were coated onto high-modulus fibers, and nickel and titanium layers were overcoated as simulated matrix materials. The objective was to coat the high-strength fibers with unreactive selected materials without degrading the fibers. The fibers were tungsten, niobium, and single-crystal sapphire, while the materials used as barrier coating layers were Al2O3, Y2O3, TiC, ZrC, WC with 14% Co, and HfO2. An ion-plating technique was used to coat the fibers. The fibers were subjected to high-temperature heat treatments to evaluate the effectiveness of the barrier layer in preventing fiber-metal interactions. Results indicate that Al2O3, Y2O3, and HfO2 can be used as barrier layers to minimize the nickel-tungsten interaction. Further investigation, including thermal cycling tests at 1090 C, revealed that HfO2 is probably the best of the three.

Veltri, R. D.↗
NASA NTRS1977

Processing eutectics in space

The examination of the Ni-Mo-Al system is discussed. Experiments were performed to examine the role of thermal gradient magnitude at the solidifying interface on the geometrical regularity of the microstructure. The difficulty in measuring the thermal gradient in the melt using superheat temperatures as high as 1800 C resulted in the examination of three liquid temperature gradient ranges. Examination of the microstructure from directionally solidified ingots using transverse sections indicated that the highest gradient runs produced microstructure of no greater regularity than runs made at lower gradients. For the Ni-Al-Mo monovariant eutectic system, the magnitude of the thermal gradient at the solidifying interface is not a controlling parameter with respect to the geometrical regularity of the microstructure, provided it is sufficient to satisfy the gradient/rate ratio needed to produce a planar interface growth.

Douglas, F. C.↗
NASA NTRS1975

Processing eutectics in space

The investigations of directional solidification have indicated the necessity of establishing a secure foundation in earth-based laboratory processing in order to properly assess low-gravity processing. Emphasis was placed on evaluating the regularity of microstructure of the rod-like eutectic Al-Al3Ni obtained under different conditions of growth involving the parameters of thermal gradient, solidification rate, and interfacial curvature. In the case of Al-Al3Ni, where the Al3Ni phase appears as facets rods, solidification rate was determined to be a controlling parameter. Zone melting of thin eutectic films showed that for films of the order of 10 to 20 micrometers thick, the extra surface energy appears to act to stabilize a regular microstructure. The results suggest that the role of low-gravity as provided in space-laboratory processing of materials is to be sought in the possibility of generating a higher thermal gradient in the solidifying ingot for a given power input-output arrangement than can be obtained under normal one-g processes.

Douglas, F. C.↗
NASA NTRS1975

Investigation to develop a method to apply diffusion barrier to high strength fibers

A radio frequency powered ion plating process was used to apply the diffusion barriers of aluminum oxide, yttrium oxide, hafnium oxide and titanium carbide to a substrate tungsten fiber. Each of the coatings was examined as to its effect on both room temperature strength and tensile strength of the base tungsten fiber. The coated fibers were then overcoated with a nickel alloy to become single cell diffusion couples. These diffusion couples were exposed to 1093 C for 24 hours, cycled between room temperature and 1093 C, and given a thermal anneal for 100 hours at 1200 C. Tensile testing and metallographic examinations determined that the hafnium oxide coating produced the best high temperature diffusion barrier for tungsten of the four coatings.

Veltri, R. D.↗
NASA NTRS1974

Processing eutectics in space

Experimental work is reported which was directed toward obtaining interface shape control while a numerical thermal analysis program was being made operational. An experimental system was developed in which the solid-liquid interface in a directionally solidified aluminum-nickel eutectic could be made either concave to the melt or convex to the melt. This experimental system provides control over the solid-liquid interface shape and can be used to study the effect of such control on the microstructure. The SINDA thermal analysis program, obtained from Marshall Space Flight Center, was used to evaluate experimental directional solidification systems for the aluminum-nickel and the aluminum-copper eutectics. This program was applied to a three-dimensional ingot, and was used to calculate the thermal profiles in axisymmetric heat flow. The results show that solid-liquid interface shape control can be attained with physically realizable thermal configurations and the magnitudes of the required thermal inputs were indicated.

Douglas, F. C.↗
NASA NTRS1974

Processing eutectics in space

Studies which have been done in an earth-based laboratory environment have generally not yielded specimens with the degree of perfection required of the eutectic microstructure to provide test data to evaluate their nonstructural applications. It has been recognized that the low-g environment of an orbiting space laboratory provides a unique environment to re-examine the process of solidification with the goal of producing better microstructures. The objective of this program is to evaluate the feasibility of using the space environment for producing eutectics with microstructures which can be of value on earth. In carrying out this objective, evaluative investigations were carried out on the technology of solidification in a 1-g environment to provide sound baseline data for planning space laboratory experiments.

Douglas, F. C.↗
NASA NTRS1974

Radial and directional solidification of metallic systems in space

Investigation of the solidification behavior of spherical specimens of Ni-12 wt % Sn and Ni-1 wt % Ag that froze radially from the surface toward the center and cylindrical specimens of Al-33 wt % Cu eutectic that froze directionally under appropriately selected conditions of thermal gradient at the solid-liquid interface and growth rate. Possible effects of vacuum and low gravity conditions, under which the spherical specimens were processed, on observed nucleation and growth phenomena are discussed. A genetic explanation is given of observed microstructures, and the distributions of alloying elements is discussed. In directionally solidified eutectic specimens a comparison is made between statistically evaluated growth defects in Skylab and in ground specimens.

Katamis, T. Z.↗
NASA NTRS1974

Research study on materials processing in space, M566 experiment

Specimens of the aluminum-33 wt% copper eutectic partially melted and resolidified in the low effective gravity of the orbiting Skylab were examined and characterized with respect to microstructural defects and thermal conductivity values. The results obtained were compared with similar evaluations of ground-based simulation melt-resolidification experiments and as-prepared unidirectionally solidified specimens. Thermal conductivity data and electrical resistivity data at temperatures from 25 C to 400 C did not show significant differences between ground and space processed specimens. A methology of evaluating the defects in the Al-Al2Cu structure was implemented. A specimen from Skylab 3 showed signs of instability in growth and several grains were found in the ingot. The specimen from Skylab 4 did not show such marked instability in growth and was found to contain fewer defects than the ground-processed specimens. This agrees with data from Georgia Institute of Technology which showed that there were fewer defects in both their Skylab 3 and 4 specimens than in ground processed specimens.

Douglas, F. C.↗
NASA NTRS1974

Eutectic solidification

The possibilities of using the low-gravity space environment for the processing of directionally solidified materials in order to remove the limitations imposed by the L-g earth environment have led to a careful evaluation of the directional solidification process and the results commonly obtained. Defects in the regularity of the microstructure have been identified as one of the most important areas where present processing technology needs to be improved. One-g environment material processing must also be carefully characterized before it can be determined if zero-g processing will produce significant benefits in eutectic and off-eutectic solidification. It is suggested that a combination of experimental and analytical thermal studies will be required to optimize the solidification process in order to minimize the structural defects which occur due to present processing techniques.

Douglas, F. C.↗
NASA NTRS1973

Application of diffusion barriers to the refractory fibers of tungsten, columbium, carbon and aluminum oxide

A radio frequency powered ion-plating system was used to plate protective layers of refractory oxides and carbide onto high strength fiber substrates. Subsequent overplating of these combinations with nickel and titanium was made to determine the effectiveness of such barrier layers in preventing diffusion of the overcoat metal into the fibers with consequent loss of fiber strength. Four substrates, five coatings, and two metal matrix materials were employed for a total of forty material combinations. The substrates were tungsten, niobium, NASA-Hough carbon, and Tyco sapphire. The diffusion-barrier coatings were aluminum oxide, yttrium oxide, titanium carbide, tungsten carbide with 14% cobalt addition, and zirconium carbide. The metal matrix materials were IN 600 nickel and Ti 6/4 titanium. Adhesion of the coatings to all substrates was good except for the NASA-Hough carbon, where flaking off of the oxide coatings in particular was observed.

Douglas, F. C.↗