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At least 271 records · Page 15

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NASA NTRS1976

Gas-phase hydrogen permeation through alpha-titanium - Surface film and dimensional effects

The two techniques normally used to determine diffusivity and permeability in metals are considered and a description is presented of experiments which had been conducted to determine the direct effect of oxide and nitride films on the membrane surface as a function of location and thickness. The test specimens used in the experiments has been machined from commercially pure titanium rod. The results of the experiments show that hydrogen transport in alpha-titanium is partially or completely controlled by surface reactions depending upon membrane wall thickness and the composition and thickness of the surface film.

Shah, K. K.↗

NASA NTRS1976

Observations of interstellar titanium toward 47 stars

Results are presented from photoelectric scans of the interstellar 3384-A line of Ti II obtained at a resolution of 3.7 km/s for 47 stars. Although the depletion of titanium from the interstellar gas is large and highly variable, its ratio to the depletion of interstellar calcium is relatively constant; titanium is less depleted than calcium by a factor of about four. A method for determining approximate electron densities from the Ca II and Ti II column densities is applied to 51 interstellar clouds.

Stokes, G. M.↗

NASA NTRS1977

Problems Associated with Attaching Strain Gages to Titanium Alloy Ti-61-4V

Weldable strain gages have shown excellent high temperature characteristics for supersonic cruise aircraft application. The spotwelding attachment method, however, has resulted in serious reductions in the fatigue life of titanium alloy (Ti-6Al-4V) fatigue specimens. The reduction is so severe that the use of weldable strain gages on operational aircraft must be prohibited. The cause of the fatigue problem is thought to be a combination of the microstructure changes in the material caused by spotwelding and the presence of the flange of the stain gage. Brazing, plating, and plasma spraying were investigated as substitutes for spotwelding. The attachment of a flangeless gage by plasma spraying provided the most improvement in the fatigue life of the titanium.

Jenkins, J. M.↗

NASA NTRS1976

Fatigue of titanium alloys in a supersonic-cruise airplane environment

The test programs conducted by several aerospace companies and NASA, summarized in this paper, studied several titanium materials previously identified as having high potential for application to supersonic cruise airplane structures. These studies demonstrate that the temperature (560 K) by itself produced no significant degradation of the materials. However, the fatigue resistance of titanium-alloy structures, in which thermal and loading effects are combined, has been studied insufficiently. The predominant topic for future study of fatigue problems in Mach 3 structures should be the influences of thermal stress particularly, the effects of thermal stress on failure location.

Imig, L. A.↗

NASA NTRS1979

Effect of nitrogen-containing plasma on adherence, friction, and wear of radiofrequency-sputtered titanium carbide coatings

Friction and wear experiments on 440C steel surfaces that were rf sputtered with titanium carbide when a small percentage of nitrogen was added to the plasma were conducted. Both X-ray photoelectron spectroscopy and X-ray diffraction were used to analyze the resultant coatings. Results indicate that the small partial pressure of nitrogen (approximately 0.5 percent) markedly improves the adherence, friction, and wear properties when compared with coatings applied to sputter-etched surfaces, oxidized surfaces, or in the presence of a small oxygen partial pressure. The improvements are related to the formation of an interface containing a mixture of the nitrides of titanium and iron, which are harder than their corresponding oxides.

Brainard, W. A.↗

NASA NTRS1979

Use of a nitrogen-argon plasma to improve adherence of sputtered titanium carbide coatings on steel

Friction and wear experiments on 440-C steel surfaces that had been RF-sputtered with titanium carbide when a small percentage of nitrogen was added to the plasma were conducted. X-ray photoelectron spectroscopy and X-ray diffraction were used to analyze the resultant coatings. Results indicate that a small partial pressure of nitrogen (about 0.5%) markedly improves the adherence, friction, and wear properties when compared with coatings applied on sputter-etched oxidized surfaces or in the presence of a small oxygen partial pressure. The improvements are related to the formation of an interface containing a mixture of the nitrides of titanium and iron, which are harder than their corresponding oxides.

Brainard, W. A.↗

NASA NTRS1979

The distribution of titanium on the lunar surface

Titanium concentrations derived from the lunar-orbiting gamma-ray experiment on Apollo 15 and 16 by analyzing a spectral interval in which the titanium signal is relatively enhanced are presented. Landing site soil values provide the reference for a regression curve from which Ti concentrations in 137 regions of adequate counting statistics are calculated. Mare Tranquillitatis contains the highest, and Mare Crisium the lowest Ti concentration, and regional values in the western maria range from 1.1% to 4.1%. Highland Ti concentrations suggest a north-south symmetry which is not consistent with previously reported Fe and Th results. Comparisons with telescopic spectral reflectance studies of the maria do not show complete agreement and suggest that effects due to Fe may not have been fully removed from the reflectance data.

Metzger, A. E.↗

NASA NTRS1980

The titanium oxide phi system

The phy system of titanium oxide has been studied in emission in the near-infrared, with the Fourier transform spectrometer at a resolution of 8000,000. Approximately 3000 lines from 25 bands of this system have been identified, including all five 0-0 and 0-1 bands corresponding to the five natural titanium isotopes. Eleven vibrational levels have been observed, and all bands have been rotationally analyzed. Band intensities are agreement with known isotopic abundances and calculated Franck-Condon factors.

Galehouse, D. C.↗

NASA NTRS1972

Flaw growth of 6Al-4V STA titanium in nitrogen tetroxide with low nitric oxide content

The sustained load flow growth characteristics of surface flowed 6Al-4V STA titanium specimens were determined when exposed to nitrogen tetroxide N2O4 having nitric oxide (NO) concentrations of 0.06 to 0.30%. Test temperatures ranged from 70 to 150 F. It was observed that the threshold stress intensity for the titanium decreased abruptly below on NO concentration of 0.18% and also decreased as the temperature increased. The threshold stress intensity was determined to be greater than or equal to 60% of the critical stress intensity for NO concentrations of 0.18 to 0.30% and temperatures of 90 and 120 F. Sustained load tests conducted in N2O4 vapor with a 0.30% NO concentration at 120 F indicated the threshold to be also greater than or equal to 60% of critical.

Bixler, W. D.↗

NASA NTRS1983

Preventing Cracks in Titanium Rotary Seals

Titanium rubs agains plastic instead of metal in new rotary seal for cryogenic pump. Friction-induced cracks in titanium parts are thereby avoided.

Ciana, J. J.↗

NASA NTRS1982

Interrelation of material microstructure, ultrasonic factors, and fracture toughness of two phase titanium alloy

The pivotal role of an alpha-beta phase microstructure in governing fracture toughness in a titanium alloy, Ti-662, is demonstrated. The interrelation of microstructure and fracture toughness is demonstrated using ultrasonic measurement techniques originally developed for nondestructive evaluation and material property characterization. It is shown that the findings determined from ultrasonic measurements agree with conclusions based on metallurgical, metallographic, and fractographic observations concerning the importance of alpha-beta morphology in controlling fracture toughness in two phase titanium alloys.

Vary, A.↗

NASA NTRS1982

Improved damage tolerance of titanium by adhesive lamination

Basic damage tolerance properties of Ti-6A1-4V titanium plate can be improved by laminating thin sheets of titanium with adhesives. Compact tension and center cracked tension specimens made from thick plate, thin sheet, and laminated plate (six plies of thin sheet) were tested. The fracture toughness of the laminated plate was 39 percent higher than the monolithic plate. The laminated plate's through the thickness crack growth rate was about 20 percent less than that of the monolithic plate. The damage tolerance life of the surface cracked laminate was 6 to over 15 times the life of a monolithic specimen. A simple method of predicting crack growth in a crack ply of a laminate is presented.

Johnson, W. S.↗

NASA NTRS1982

Interstellar titanium abundances toward 19 high-latitude stars

The 3384 absorption line of interstellar Ti II has been observed at high resolution along lines of sight toward nine nearly aligned pairs of foreground disk and background halo stars, the latter having z-distance greater than 500 pc. The primary result is the great strength of Ti II absorption perpendicular to the plane of the Galaxy. Compared with the well-studied disk abundances, there is apparently a vertical gradient of titanium depletion above the galactic plane. The gaseous titanium abundance relative to hydrogen increases with z-distance and with LSR velocity by factors exceeding 20 and can reach nearly solar proportions.

Albert, C. E.↗

NASA NTRS1982

Long titanium heat pipes for high-temperature space radiators

Titanium heat pipes are being developed to provide light weight, reliable heat rejection devices as an alternate radiator design for the Space Reactor Power System (SP-100). The radiator design includes 360 heat pipes, each of which is 5.2 m long and dissipates 3 kW of power at 775 K. The radiator heat pipes use potassium as the working fluid, have two screen arteries for fluid return, a roughened surface distributive wicking system, and a D shaped cross section container configuration. A prototype titanium heat pipe, 5.5 m long, was fabricated and tested in space simulating conditions. Results from startup and isothermal operation tests are presented. These results are also compared to theoretical performance predictions that were used to design the heat pipe initially.

Girrens, S. P.↗

NASA NTRS1983

Fabrication and evaluation of cold/formed/weldbrazed beta-titanium skin-stiffened compression panels

The room temperature and elevated temperature buckling behavior of cold formed beta titanium hat shaped stiffeners joined by weld brazing to alpha-beta titanium skins was determined. A preliminary set of single stiffener compression panels were used to develop a data base for material and panel properties. These panels were tested at room temperature and 316 C (600 F). A final set of multistiffener compression panels were fabricated for room temperature tests by the process developed in making the single stiffener panels. The overall geometrical dimensions for the multistiffener panels were determined by the structural sizing computer code PASCO. The data presented from the panel tests include load shortening curves, local buckling strengths, and failure loads. Experimental buckling loads are compared with the buckling loads predicted by the PASCO code. Material property data obtained from tests of ASTM standard dogbone specimens are also presented.

Royster, D. M.↗

NASA NTRS1982

Superplastic forming/weld-brazing of titanium skin-stiffened compression panels

A study was conducted to exploit the processing advantages of superplastic forming and weld-brazing for the fabrication of titanium skin-stiffened structural components. Small titanium compression panels were fabricated and tested at room temperature. Stiffeners having configurations of a conventional hat shape, beaded shaped web, ribbed shaped web, or stepped shaped web were investigated. The data from the panel tests included load-shortening curves, local buckling strengths, and failure loads. Experimental buckling loads were compared with buckling loads calculated using a finite-element analysis. The superplastic formed/weld-brazed panels having complex shaped stiffeners developed from 20 to 58 percent higher local buckling strengths than panels with conventionally shaped stiffeners.

Royster, D. M.↗

NASA NTRS1982

Long titanium heat pipes for high-temperature space radiators

Titanium heat pipes are being developed to provide light weight, reliable heat rejection devices as an alternate radiator design for the Space Reactor Power System (SP-100). The radiator design includes 360 heat pipes, each of which is 5.2 m long and dissipates 3 kW of power at 775 K. The radiator heat pipes use potassium as the working fluid, have two screen arteries for fluid return, a roughened surface distributive wicking system, and a D-shaped cross-section container configuration. A prototype titanium heat pipe, 5.5-m long, has been fabricated and tested in space-simulating conditions. Results from startup and isothermal operation tests are presented. These results are also compared to theoretical performance predictions that were used to design the heat pipe initially.

Girrens, S. P.↗

NASA NTRS1983

Damage tolerance evaluation of adhesively laminated titanium

Johnson, W. S.↗