Effect of stress on microsegregation of hydrogen at elevated temperatures in titanium and Ti-8Al-1Mo-1V
Stress effect on hydrogen distribution at high temperatures in titanium and Ti-Al-Mo-V alloy
Mackay, T. L.↗
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Relative susceptibility of titanium alloys to hot-salt stress-corrosion
Susceptibility of titanium alloys to hot-salt stress-corrosion cracking increased as follows: Ti-2Al-11Sn-5Zr-0.2Si(679), Ti-6Al-2Sn-4Zr-2Mo(6242), Ti-6Al-4V(64), Ti-6Al-4V-3Co(643), Ti-8Al-1Mo-1V(811), and Ti-13V-11Cr-3A1(13-11-3). The Ti-5Al-6Sn-2Zr-1Mo-0.25Si(5621S) alloy was both the least and most susceptible depending on heat treatment. Such rankings can be drastically altered by heat-to-heat and processing variations. Residual compressive stresses and cyclic exposures also reduce susceptibility to stress-corrosion. Simulated turbine-engine compressor environmental variables such as air velocity, pressure, dewpoint, salt concentration, and salt deposition temperature have only minor effects. Detection of substantial concentrations of hydrogen in all corroded alloys confirmed the existence of a hydrogen embrittlement mechanism.
Gray, H. R.↗
Fretting wear in titanium, Monel-400, and cobalt 25-percent-molybdenum using scanning electron microscopy
Damage scar volume measurements taken from like metal fretting pairs combined with scanning electron microscopy observations showed that three sequentially operating mechanisms result in the fretting of titanium, Monel-400, and cobalt - 25-percent molybdenum. Initially, adhesion and plastic deformation of the surface played an important role. This was followed after a few hundred cycles by a fatigue mechanism which produced spall-like pits in the damage scar. Finally, a combination of oxidation and abrasion by debris particles became most significant. Damage scar measurements made on several elemental metals after 600,000 fretting cycles suggested that the ratio of oxide hardness to metal hardness was a measure of the susceptibility of a metal to progressive damage by fretting.
Bill, R. C.↗
Ignition of Fuel Vapors Beneath Titanium Aircraft Skins Exposed to Lightning
Hot-spot and puncture ignition of fuel vapors by simulated lightning discharges was studied experimentally. The influences of skin coating, skin structure, discharge polarity, skin thickness, discharge current level, and current duration were measured and interpreted. Ignition thresholds are reported for titanium alloy constructed as sheets, sheets coated with sealants, and sandwich skins. Results indicated that the ignition threshold charge transfer for coated sheets, honeycomb, and truss skins is respectively about 200%, 400%, 800% that of bare alloy sheet of .102 cm (.040 in.)-thickness. It was found that hot-spot ignition can occur well after termination of the arc, and that sandwich materials allow ignition only if punctured.
Kosvic, T. C.↗
Fabrication of titanium thermal protection system panels by the NOR-Ti-bond process
A method for fabricating titanium thermal protection system panels is described. The method has the potential for producing wide faying surface bonds to minimize temperature gradients and thermal stresses resulting during service at elevated temperatures. Results of nondestructive tests of the panels are presented. Concepts for improving the panel quality and for improved economy in production are discussed.
Wells, R. R.↗
The effect of alloy composition on the mechanism of stress corrosion cracking of titanium alloys in aqueous environments
The effects of alloy composition on the aqueous stress corrosion of titanium alloys were studied with emphasis on determining the interrelations among composition, phase structure, and deformation and fracture properties of the alpha phase in alpha-beta alloys. Accomplishments summarized include the effects of alloy composition on susceptibility, and metallurgical mechanisms of stress-corrosion cracking.
Boyd, J. D.↗
An electrochemical model for hot-salt stress-corrosion of titanium alloys
An electrochemical model of hot-salt stress-corrosion cracking of titanium alloys is proposed based on an oxygen-concentration cell. Hydrogen embrittlement is proposed as the direct cause of cracking, the hydrogen being generated as the results of the hydrolysis of complex halides formed at the shielded anode of the electrochemical cell. The model found to be consistent with the diverse observations made both in this study and by many investigators in this field.
Garfinkle, M.↗
Valve, normally closed, titanium Pyronetics model 1426
Performance tests of the explosive actuated, normally closed titanium valve 1426, are outlined. The valves are used to control hydrazine flow in a monopropellant thruster. Data cover pressure tests, internal and external leakage tests, flow control tests, and actuator tests. No failures were noted in any of the tests.
Avalos, E.↗
The 1200 C cyclic oxidation behavior of two nickel-aluminum alloys (Ni3AL and NiAl) with additions of chromium, silicon, and titanium
The alloys Ni3Al and NiAl with and without 1 and 3 atomic percent chromium, silicon, and titanium replacing the aluminum were cyclically oxidized at 1200 C for times to 200 hours, and the results were compared with those obtained with the alloy B-1900 subjected to the same oxidation process. The evaluation was based on metal recession, specific weight change, metallography, electron microprobe analysis, and X-ray diffraction. The oxidation resistance of Ni3Al was improved by Si, unaffected by Ti, and degraded by Cr. The oxidation resistance of NiAl was slightly improved by Ti, unaffected by Si, and degraded by Cr. The oxidation resistance of Ni3Al with 1 atomic percent Si was nearly equal to that of NiAl. Alloy B-1900 exhibited oxidation resistance comparable to that of Ni3Al + Cr compositions.
Lowell, C. E.↗
Materials data handbook. Titanium 6Al-4V
A summary of the materials property information for Titanium 6Al-4V alloy is presented. The scope of the information includes physical and mechanical properties at cryogenic, ambient, and elevated temperatures. Information on material procurement, metallurgy of the alloy, corrosion, environmental effects, fabrication, and bonding is developed.
Muraca, R. F.↗
Investigation of the reaction of 5Al-2.5Sn titanium with hydrogen at subzero temperature
An investigation of the effect of temperature on the surface hydriding reaction of 5Al-2.5Sn titanium exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 F to -160 F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultrapure hydrogen atmosphere. Reaction times up to 1458 hours were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 F; as much as 1 mil surface hydriding being observed after exposure for 162 hours. The amount of hydriding appeared to decrease with decreasing temperature at 75 F, -36 F, and -76 F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 hours at -110 F or -160 F. Tensile properties were unaffected by surface hydriding of the severity developed in this program (up to 1 mil thick) as determined by slow strain rate testing of hydrided sheet tensile samples.
Williams, D. N.↗
Mechanism of the oxidation of titanium disilicide.
Study of the oxidation of TiSi2 at temperatures of 300 to 1300 C. Wafers prepared using the techniques of powder metallurgy had densities of 95 to 98% of the theoretical value. On oxidation at temperatures up to 600 C, the polished wafers formed a protective, titania-silica glass. The rate data indicate a complex surface and diffusion-limited mechanism. Above 600 deg C, the oxide consisted of an amorphous SiO2 film with crystalline islands of TiO2 (rutile). From 1000 to 1300 C, parabolic kinetics with an activation energy of 21.3 kcal/mole were observed. These data are consistent with a model in which the rate-determining step is the diffusion of oxygen through the silica film with the simultaneous diffusion of titanium from the substrate to the islands of rutile growing on top of the amorphous silica.
Schwettmann, F. N.↗
Effect of initial hydrogen content of a titanium alloy on susceptibility to hot salt stress corrosion.
The influence of the initial hydrogen content of a titanium alloy on subsequent resistance to hot salt stress corrosion embrittlement and cracking was investigated. A Ti-8Al-1Mo-1V alloy was tested in four conditions: mill annealed (70 ppm H), duplex annealed (70 ppm H), vacuum annealed to an intermediate (36 ppm H) and a low (9 ppm H) hydrogen level. Material annealed at 650 C (duplex condition) exhibited resistance to hot salt stress corrosion superior to that exhibited by material in the mill annealed condition. Reduction of the alloy hydrogen content from 70 to as low as 9 ppm did not influence resistance to hot salt stress corrosion embrittlement or cracking.
Gray, H. R.↗
Hot-salt stress-corrosion of titanium alloys as related to turbine engine operation.
Demonstration that the major variables influencing hot-salt stress-corrosion of titanium alloys are alloy processing conditions, heat-to-heat variations and composition, surface condition, and cyclic exposures. Under simulated compressor environmental conditions the commonly used 64 alloy is creep limited and not stress-corrosion limited. Cyclic exposures to stress-corrosion conditions are not as detrimental as continuous exposures for equivalent total times.
Gray, H. R.↗
Improved diffusion welding and roll welding of titanium alloys
Auto-vacuum cleaning technique was applied to titanium parts prior to welding. This provides oxide-free welding surfaces. Diffusion welding can be accomplished in as little as five minutes of hot pressing. Roll welding can be accomplished with only ten percent deformation.
Holko, K. H.↗
Materials data handbook on titanium 6Al-4V
Handbook has been prepared which describes latest property information on titanium 6Al-4V. Scope of information presented includes physical- and mechanical-property data at cryogenic, ambient, and elevated temperatures, supplemented with useful information in such areas as material procurement,metallurgy of alloy, corrosion, environmental effects, fabrication, and joining technology.
Muraca, R. F.↗
Irradiation effects on 17-7 PH stainless steel, A-201 carbon steel, and titanium-6-percent-aluminum-4-percent-vanadium alloy
Irradiation effects on three materials from the NASA Plum Brook Reactor Surveillance Program were determined. An increase of 105 K in the nil-ductility temperature for A-201 steel was observed at a fluence of approximately 3.1 x 10 to the 18th power neutrons/sq cm (neutron energy E sub n greater than 1.0 MeV). Only minor changes in the mechanical properties of 17-7 PH stainless steel were observed up to a fluence of 2 x 10 to the 21st power neutrons/sq cm (E sub n greater than 1.0 MeV). The titanium-6-percent-aluminum-4-percent-vanadium alloy maintained its notch toughness up to a fluence of 1 x 10 to the 21st power neutrons/sq cm (E sub n greater than 1.0 MeV).
Hasse, R. A.↗
Valve, normally open, titanium: Pyronetics Model 1425
An operating test series was applied to two explosive actuated, normally open, titanium valves. There were no failures. Tests included: proof pressure and external leakage test, gross leak test, post actuation leakage test, and burst pressure test.
Avalos, E.↗