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NASA NTRS1981

Thermal and aerothermal performance of a titanium multiwall thermal protection system

A metallic thermal protection system (TPS) concept the multiwall designed for temperature and pressure at Shuttle body point 3140 where the maximum surface temperature is approximately 811 K was tested to evaluate thermal performance and structural integrity. A two tile model of titanium multiwall and a model consisting of a low temperature reusable surface insulation (LRSI) tiles were exposed to 25 simulated thermal and pressure Shuttle entry missions. The two systems performed the same, and neither system deteriorated during the tests. It is indicated that redesign of the multiwall tiles reduces tile thickness and/or weight. A nine tile model of titanium multiwal was tested for radiant heating and aerothermodynamics. Minor design changes that improve structural integrity without having a significant impact on the thermal protection ability of the titanium multiwall TPS are identified. The capability of a titanium multiwall thermal protection system to protect an aluminum surface during a Shuttle type entry trajectory at locations on the vehicle where the maximum surface temperature is below 811 K is demonstrated.

Avery, D. E.↗

NASA NTRS1985

Advances in Joining Techniques Used in Development of SPF/DB Titanium Sandwich Reinforced with Metal Matrices

Three and four-sheet expanded titanium sandwich sheets have been developed at Douglas Aircraft Company, a division of McDonnell Douglas Corporation, under contract to NASA Langley Research Center. In these contracts, spot welding and roll seam welding are used to join the core sheets. These core sheets are expanded to the face sheets and diffusion bonded to form various type cells. The advantages of various cell shapes and the design parameters for optimizing the wing and fuselage concepts are discussed versus the complexity of the spot weld pattern. In addition, metal matrix composites of fibers in an aluminum matrix encapsulated in a titanium sheath are aluminum brazed successfully to the titanium sandwich face sheets. The strength and crack growth rate of the superplastic-formed/diffusion bonded (SPF/DB) titanium sandwich with and without the metal matrix composites are described.

Fischler, J. E.↗

NASA NTRS1989

The effects of hydrogen embrittlement of titanium

Titanium alloys, by virtue of their attractive strength to density ratio, fatigue, fracture toughness and corrosion resistance are now commonly used in various aerospace and marine applications. The cost, once very expensive, has been reduced, making titanium even more of a competitive material today. Titanium and titanium alloys have a great affinity to several elements. Hydrogen, even in small amounts, can cause embrittlement, which in turn causes a reduction in strength and ductility. The reduction of strength and ductility is the subject of this investigation.

Taylor, Delbert J.↗

NASA NTRS1992

Lightweight Protective Coatings For Titanium Alloys

Lightweight coating developed to protect titanium and titanium aluminide alloys and titanium-matrix composite materials from attack by environment when used at high temperatures. Applied by sol-gel methods, and thickness less than 5 micrometers. Reaction-barrier and self-healing diffusion-barrier layers combine to protect titanium alloy against chemical attack by oxygen and nitrogen at high temperatures with very promising results. Can be extended to protection of other environmentally sensitive materials.

Wiedemann, Karl E.↗

NASA NTRS1992

Lunar-derived titanium alloys for hydrogen storage

Hydrogen gas, which plays an important role in many projected lunar power systems and industrial processes, can be stored in metallic titanium and in certain titanium alloys as an interstitial hydride compound. Storing and retrieving hydrogen with titanium-iron alloy requires substantially less energy investment than storage by liquefaction. Metal hydride storage systems can be designed to operate at a wide range of temperatures and pressures. A few such systems have been developed for terrestrial applications. A drawback of metal hydride storage for lunar applications is the system's large mass per mole of hydrogen stored, which rules out transporting it from earth. The transportation problem can be solved by using native lunar materials, which are rich in titanium and iron.

Love, S.↗

NASA NTRS1993

Thermal coatings for titanium-aluminum alloys

Titanium aluminides and titanium alloys are candidate materials for use in hot structure and heat-shield components of hypersonic vehicles because of their good strength-to-weight characteristics at elevated temperature. However, in order to utilize their maximum temperature capability, they must be coated to resist oxidation and to have a high total remittance. Also, surface catalysis for recombination of dissociated species in the aerodynamic boundary layer must be minimized. Very thin chemical vapor deposition (CVD) coatings are attractive candidates for this application because of durability and very light weight. To demonstrate this concept, coatings of boron-silicon and aluminum-boron-silicon compositions were applied to the titanium-aluminides alpha2 (Ti-14Al-21Nb), super-alpha2 (Ti-14Al-23-Nb-2V), and gamma (Ti-33Al-6Nb-1Ta) and to the titanium alloy beta-21S (Ti-15Mo-3Al-3Nb-0.2Si). Coated specimens of each alloy were subjected to a set of simulated hypersonic vehicle environmental tests to determine their properties of oxidation resistance, surface catalysis, radiative emittance, and thermal shock resistance. Surface catalysis results should be viewed as relative performance only of the several coating-alloy combinations tested under the specific environmental conditions of the LaRC Hypersonic Materials Environmental Test System (HYMETS) arc-plasma-heated hypersonic wind tunnel. Tests were also conducted to evaluate the hydrogen transport properties of the coatings and any effects of the coating processing itself on fatigue life of the base alloys. Results are presented for three types of coatings, which are as follows: (1) a single layer boron silicon coating, (2) a single layer aluminum-boron-silicon coating, and (3) a multilayer coating consisting of an aluminum-boron-silicon sublayer with a boron-silicon outer layer.

Cunnington, George R.↗

NASA NTRS1996

Development of Low Density Titanium Alloys for Structural Applications

In this report the results of a program designed to reduce the density of titanium by adding magnesium are presented. Because these two elements are immiscible under conventional ingot metallurgy techniques, two specialized powder metallurgy methods namely, mechanical alloying (MA) and physical vapor deposition (PVD) were implemented. The mechanical alloying experiments were done both at the University of Idaho and at the Defense Research Agency in UK. Since titanium is reactive with interstitial elements, a secondary goal of this research was to correlate solubility extensions with interstitial contamination content, especially oxygen and nitrogen. MA was carried out in SPEX 8000 shaker mils and different milling containers were utilized to control the level of contamination. Results showed that solubilities of Mg in Ti were obtained up to 28 at.% (16.4 wt. %) Mg in Ti for Ti-39.6 at. % (25 wt. %) Mg alloys, which greatly exceed those obtained under equilibrium conditions. This reflects a density reduction of approximately 26 %. Contamination of oxygen and nitrogen seemed to increase the solubility of magnesium in titanium in some cases; however, we were not able to make a clear correlation between contamination levels with solubilities. Work at the DRA has emphasized optimization of present PVD equipment, specifically composition and temperature control. Preliminary PVD data has shown Ti-Mg deposits have successfully been made up to 2 mm thick and that solubility extensions were achieved. The potential for density reduction of titanium by alloying with magnesium has been demonstrated; however, this work has only scratched the surface of the development of such low density alloys. Much research is needed before such alloys could be implemented into industry. Further funding is required in order to optimize the MA/PVD processes including contamination control, determination of optimal alloy compositions, microstructure development, and mechanical property determination.

Froes, F. H.↗

NASA NTRS1992

Thermodynamics, Solubility, and Diffusivity of Oxygen in Titanium and Ti-Al Alloys

Titanium aluminides and titanium aluminide-based composites are attractive candidate materials for high-temperature structural applications. As these materials may be exposed to oxidizing environments durine their use at elevated temperatures, it is essential that they possess a good oxidation resistance. Previous studies have shown that the oxidation resistance of Al-rich alloys in the Ti-Al system is superior to that of the Ti-rich alloys. The scales formed on the surface of the Al-rich and Ti-rich alloys have been reported to be predominantly Al2O3 and TiO2, respectively. Since the relative stabilities of the oxides of Al and Ti at various temperatures and oxygen pressures can be assessed from their thermodynamic data, it is possible, With the help of thermodynamic calculations, to determine the compositions of the alloys which would form scales of Al2O3, TiO(x) or a ternary oxide such as TiAl2O5 during oxidation at a given temperature. The thermodynamic calculations require reliable activity data for the Ti-Al system. These data have not been determined for the entire composition and temperature range of interest. Using the data available in the literature, recently performed thermodynamic calculations and concluded that the stable oxide changed from TiO to Al2O3 in the existence region of the tial phase. In the case of titanium aluminide-based composites, another major concern is the mutual chemical compatibility of the matrix material with the reinforcement phase. Fibers of SiC, TiB2 and Al2O3 are currently being investigated for reinforcement of titanium aluminide matrices.

Mehrotra, Gopal M.↗

NASA NTRS2000

Micromechanical Characterization and Texture Analysis of Direct Cast Titanium Alloys Strips

This research was conducted to determine a post-processing technique to optimize mechanical and material properties of a number of Titanium based alloys and aluminides processed via Melt Overflow Solidification Technique (MORST). This technique was developed by NASA for the development of thin sheet titanium and titanium aluminides used in high temperature applications. The materials investigated in this study included conventional titanium alloy strips and foils, Ti-1100, Ti-24Al-11Nb (Alpha-2), and Ti-48Al-2Ta (Gamma). The methodology used included micro-characterization, heat-treatment, mechanical processing and mechanical testing. Characterization techniques included optical, electron microscopy, and x-ray texture analysis. The processing included heat-treatment and mechanical deformation through cold rolling. The initial as-cast materials were evaluated for their microstructure and mechanical properties. Different heat-treatment and rolling steps were chosen to process these materials. The properties were evaluated further and a processing relationship was established in order to obtain an optimum processing condition. The results showed that the as-cast material exhibited a Widmanstatten (fine grain) microstructure that developed into a microstructure with larger grains through processing steps. The texture intensity showed little change for all processing performed in this investigation.

Source record↗

NASA NTRS1949

Investigation of Conditions of Titanium Carbonization - IV

In a previous paper, results are presented of accurate investigations of the processes of titanium carbonization and the succeeding titanium carbide decarbonization as related to the phenomenon of the graphitization of soot by heating at a constant temperature in atmospheres of pure hydrogen and carbon monoxide. These tests showed that the processes of titanium carbonization-decarbonization in an atmosphere of pure gases without nitrogen proceed in the same direction as the analogous processes under the conditions of the production furnace. In this case, however, the presence of admixtures of nitrogen changes the quantitative results of the decarbonization process. Thermodynamic computations confirming the results of previous tests conducted at atmospheric pressure and additional tests of titanium carbonization at lowered pressures are presented herein.

Meerson, G. A.↗

NASA NTRS1997

An Oxidation-Resistant Coating Alloy for Gamma Titanium Aluminides

Titanium aluminides based on the g-phase (TiAl) offer the potential for component weight savings of up to 50 percent over conventional superalloys in 600 to 850 C aerospace applications. Extensive development efforts over the past 10 years have led to the identification of "engineering" gamma-alloys, which offer a balance of room-temperature mechanical properties and high-temperature strength retention. The gamma class of titanium aluminides also offers oxidation and interstitial (oxygen and nitrogen) embrittlement resistance superior to that of the alpha(sub 2) (Ti3Al) and orthorhombic (Ti2AlNb) classes of titanium aluminides. However, environmental durability is still a concern, especially at temperatures above 750 to 800 C. Recent work at the NASA Lewis Research Center led to the development of an oxidation-resistant coating alloy that shows great promise for the protection of gamma titanium aluminides.

Brady, Michael P.↗

NASA NTRS2003

Particulate Titanium Matrix Composites Tested-Show Promise for Space Propulsion Applications

New manufacturing technologies can now produce uniformly distributed particle strengthened titanium matrix composites (TMCs) at lower cost than many types of continuous-fiber composites. The innovative process results in near-final-shape components having a material stiffness up to 26-percent greater than that of components made with conventional titanium materials. This benefit is achieved with no significant increase in the weight of the component. The improved mechanical performance and low-cost manufacturing capability motivated a review of particulate-reinforced metal composite technology as a way to lower the cost and weight of space-access propulsion systems. Focusing on the elevated-temperature properties of titanium alloy Ti-6Al-4V as the matrix material, researchers at the NASA Glenn Research Center conducted experiments to verify the improved performance of the alloy containing 10 wt% of ceramic titanium carbide (TiC) particles. The appropriate blend of metal and ceramic powder underwent a series of cold and hot isostatic pressing procedures to yield bar stock. A set of round dogbone specimens was manufactured from a small sample of the bars. The TMC material proved to have good machinability at this particle concentration as there was no difficulty in producing high-quality specimens.

Thesken, John C.↗

NASA NTRS2008

Risk Assessment for Titanium Pressure Vessels Operating Inside the ARES I's Liquid Hydrogen Tank Environment

Titanium alloy (Ti-6-4) is currently being proposed for the manufacturing of pressure vessels (PV) for storage of compressed helium gas, which are mounted inside the ARES I's liquid hydrogen (LH2) tank. At cryogenic temperature, titanium alloys usually have the highest strength-to-weight ratio property and have been considered as the metallic materials of choice for lightweight PV operating in LH2 environment. Titanium PV s are also considered as heritage hardware because they have been used by NASA for the Saturn IV-B rocket s LH2 tank in the mid 1960 s. However, hydrogen embrittlement is possible if Ti-6-4 alloy is exposed to gaseous hydrogen at certain pressure and temperature during the LH2 tank filling and draining operations on the launch pad, and during the J2X engine burn period for the ARES I s upper stage. Additionally, the fracture toughness and ductility properties of Ti-6-4 are significantly decreased at cryogenic temperature. These factors do not necessary preclude the use of titanium PV in hydrogen or at cryogenic applications; however, their synergistic effects and the material damage tolerance must be accounted for in the mission life assessment for PV s, which are considered as fracture critical hardware. In this paper, an overview of the risk assessment for Ti-6-4 alloy, strategy to control hydrogen embrittlement and brief metallic material trade study for PV operating in LH2 tank will be presented.

Lee, Jonathan A.↗

NASA NTRS2009

Machined Titanium Heat-Pipe Wick Structure

Wick structures fabricated by machining of titanium porous material are essential components of lightweight titanium/ water heat pipes of a type now being developed for operation at temperatures up to 530 K in high-radiation environments. In the fabrication of some prior heat pipes, wicks have been made by extruding axial grooves into aluminum unfortunately, titanium cannot be extruded. In the fabrication of some other prior heat pipes, wicks have been made by in-situ sintering of metal powders shaped by the use of forming mandrels that are subsequently removed, but in the specific application that gave rise to the present fabrication method, the required dimensions and shapes of the heat-pipe structures would make it very difficult if not impossible to remove the mandrels due to the length and the small diameter. In the present method, a wick is made from one or more sections that are fabricated separately and assembled outside the tube that constitutes the outer heat pipe wall. The starting wick material is a slab of porous titanium material. This material is machined in its original flat configuration to form axial grooves. In addition, interlocking features are machined at the mating ends of short wick sections that are to be assembled to make a full-length continuous wick structure. Once the sections have been thus assembled, the resulting full-length flat wick structure is rolled into a cylindrical shape and inserted in the heatpipe tube (see figure). This wick-structure fabrication method is not limited to titanium/water heat pipes: It could be extended to other heat pipe materials and working fluids in which the wicks could be made from materials that could be pre-formed into porous slabs.

Rosenfeld, John H.↗

NASA NTRS2009

Intermetallic Nickel-Titanium Alloys for Oil-Lubricated Bearing Applications

An intermetallic nickel-titanium alloy, NITINOL 60 (60NiTi), containing 60 wt% nickel and 40 wt% titanium, is shown to be a promising candidate material for oil-lubricated rolling and sliding contact applications such as bearings and gears. NiTi alloys are well known and normally exploited for their shape memory behavior. When properly processed, however, NITINOL 60 exhibits excellent dimensional stability and useful structural properties. Processed via high temperature, high-pressure powder metallurgy techniques or other means, NITINOL 60 offers a broad combination of physical properties that make it unique among bearing materials. NITINOL 60 is hard, electrically conductive, highly corrosion resistant, less dense than steel, readily machined prior to final heat treatment, nongalling and nonmagnetic. No other bearing alloy, metallic or ceramic encompasses all of these attributes. Further, NITINOL 60 has shown remarkable tribological performance when compared to other aerospace bearing alloys under oil-lubricated conditions. Spiral orbit tribometer (SOT) tests were conducted in vacuum using NITINOL 60 balls loaded between rotating 440C stainless steel disks, lubricated with synthetic hydrocarbon oil. Under conditions considered representative of precision bearings, the performance (life and friction) equaled or exceeded that observed with silicon nitride or titanium carbide coated 440C bearing balls. Based upon this preliminary data, it appears that NITINOL 60, despite its high titanium content, is a promising candidate alloy for advanced mechanical systems requiring superior and intrinsic corrosion resistance, electrical conductivity and nonmagnetic behavior under lubricated contacting conditions.

DellaCorte, C.↗

NASA NTRS2010

The Development of Titanium Alloys for Application in the Space Shuttle Main Engine

The high-strength-to-weight ratio of titanium alloys, particularly at cryogenic temperatures, make them attractive for application in rocket engines - offering the potential of superior performance while minimizing component weight. This was particularly attractive for rotating components, such as pump impellers, where titanium alloys presented the potential to achieve a major advance in rotational tip speed, with a reduction in stages and resultant saving in pump weight and complexity. The investigation into titanium alloys for application in cryogenic turbopumps began in the early 1960's. However, it was found that the reactivity of titanium limited applications and produced unique processing challenges. Specialized chemical compositions and processing techniques had to be developed. A substantial amount of material properties testing and trials in experimental turbopumps occurred, ultimately leading to application in the Space Shuttle Main Engine. One particular alloy stood out for use at liquid hydrogen temperatures, Ti-5Al-2.5Sn ELI. This alloy was employed for several critical components. This presentation deals with the development effort, the challenges that were encountered and operational experiences with Ti-5Al-2.5Sn ELI in the SSME.

Halchak, John A.↗

NASA NTRS2010

Nickel-Titanium Alloys: Corrosion "Proof" Alloys for Space Bearing, Components and Mechanism Applications

An intermetallic nickel-titanium alloy, 60NiTi (60wt%Ni, 40wt%Ti), is shown to be a promising candidate tribological material for space mechanisms. 60NiTi offers a broad combination of physical properties that make it unique among bearing materials. 60NiTi is hard, electrically conductive, highly corrosion resistant, readily machined prior to final heat treatment, and is non-magnetic. Despite its high titanium content, 60NiTi is non-galling even under dry sliding. No other bearing alloy, metallic or ceramic, encompasses all of these attributes. Since 60NiTi contains such a high proportion of titanium and possesses many metallic properties, it was expected to exhibit poor tribological performance typical of titanium alloys, namely galling type behavior and rapid lubricant degradation. In this poster-paper, the oil-lubricated behavior of 60NiTi is studied.

DellaCorte, Christopher↗

NASA NTRS2010

Hypervelocity Impact of Unstressed and Stressed Titanium in a Whipple Configuration in Support of the Orion Crew Exploration Vehicle Service Module Propellant Tanks

Hypervelocity impacts were performed on six unstressed and six stressed titanium coupons with aluminium shielding in order to assess the effects of the partial penetration damage on the post impact micromechanical properties of titanium and on the residual strength after impact. This work is performed in support of the definition of the penetration criteria of the propellant tanks surfaces for the service module of the crew exploration vehicle where such a criterion is based on testing and analyses rather than on historical precedence. The objective of this work is to assess the effects of applied biaxial stress on the damage dynamics and morphology. The crater statistics revealed minute differences between stressed and unstressed coupon damage. The post impact residual stress analyses showed that the titanium strength properties were generally unchanged for the unstressed coupons when compared with undamaged titanium. However, high localized strains were shown near the craters during the tensile tests.

Nahra, Henry K.↗