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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Effect of alloy chemistry and exposure conditions on the oxidation of titanium

Multiwall is a new thermal protection system concept for advanced space transportation vehicles. The system consists of discrete panels made up of multiple layers of foil gage metal. Titanium is the proposed candidate metal for multiwall panels in the reentry temperature range up to 675 C. Oxidation and embrittlement are the principal concerns related to the use of Ti in heat shield applications. The results of a broad study on the oxidation kinetics of several titanium alloys subjected to different exposure conditions are described. The alloys include commercially pure titanium, Ti-6Al-4V, and Ti-6Al-2Sn-4Zr-2Mo. Oxidation studies were performed on these alloys exposed at 704 C in 5-760 torr air pressure and 0 to 50% relative humidity. The resulting weight gains were correlated with oxide thickness and substrate contamination. The contamination depth and weight gains due to solid solutioning were obtained from microhardness depth profiles and hardness versus weight percent oxygen calibration data.

Unnam, J.↗
NASA NTRS1985

Corrosion of metals by hydrazine

The mechanism of corrosion of metals by hydrazine has been studied by means of coupons in sealed ampoules and by electrochemical techniques. The variables considered were temperature, CO2 impurity level, alloy composition and microcrystalline structure. The coupon studies, to date, verify that increasng temperature and the presence of CO2 does increase the corrosion rate as expected. The presence of molybdenum in stainless steels to the 3 percent level is not necessarily deleterious, contrary to published reports. The influence of microcrystalline structure and surface characteristics are more dominant effects. However, with Ti-6Al-4V, two different microcrystalline structures showed no significant differences. Corrosion rates of CRES 304 L in hydrazine have also been measured by several electrochemical techniques such as Tafel plots, polarization resistance and A. C. Impedance. This is the first documented work to show that A. C. Impedance can be used with non-aqueous solvents. Preliminary data correlated satisfactorily with the results of the coupon studies.

Lawton, E. A.↗
NASA NTRS1986

Adhesive evaluation of thin films of LARC-TPI and LARC-TPI with 5 mol % ODA

A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol % of 4,4'-oxydianiline (ODA), designated as LARC-TPI/ODA in the report, supplied by Mitsui Toatsu Chemicals, Incorporated (MTCI), Japan, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. The LARC-TPI/ODA had been shown by MTCI to possess more flow than thermoplastic LARC-TPI and was, therefore, evaluated and compared to the LARC-TPI. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, Tg. The mode of failure was also reported. Thermal exposure at 204C for 500 and 1000 hrs and a 72-hour water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at RT, 177C, 204C, and 232C before and after exposures.

Progar, D. J.↗
NASA NTRS1986

Study on effects of powder and flake chemistry and morphology on the properties of Al-Cu-Mg-X-X-X powder metallurgy advanced aluminum alloys

A study was conducted: (1) to develop rapid solidification processed (RSP) dispersoid-containing Al-3Cu-2Li-1Mg-0.2Zr alloys as substitutes for titanium alloys and commercial 2XXX aluminum alloys for service to at least 150 C; and (2) to develop RSP Al-4Li-Cu-Mg-Zr alloys as substitutes for high-strength commercial 7XXX alloys in ambient-temperature applications. RSP Al-3Cu-2Li-1Mg-0.2Zr alloys have density-normalized yield stresses at 150 C up to 52% larger than that of 2124-T851 and up to 30% larger than that of Ti-6Al-4V. Strength at 150 C in these alloys is provided by thermally stable delta' (Al3Li), T1 (Al2LiCu), and S' (Al2CuMg) precipitates. Density-normalized yield stresses of RSP Al-3Cu-2Li-1Mg-0.2Zr alloys are up to 100% larger than that of 2124-T851 and equivalent to that of Al-8Fe-4Ce at 260 C. Strength in the RSP alloys at 260 C is provided by incoherent dispersoids and subboundary constituent particles such as T1 and S. The RSP alloys are attractive substitutes in less than or = 100-h exposures for 2xxx and Al-4Fe-Ce alloys up to 260 C and for titanium alloys up to 150 C. RSP Al-4Li-Cu-Mg-Zr alloys have ambient-temperature yield and ultimate tensile stresses similar to that of 7050-T7651, and are 14% less dense. RSP Al-4Li-0.5Cu-1.5Mg-0.2Zr has a 20% higher specific yield stress, 40% higher specific elastic modulus, and superior corrosion resistance compared to the properties of 7050-T7651. Strength in the Al-4Li-Cu-Mg-Zr alloy class is primarily provided by the substructure and delta' precipitates and is independent of Cu:Mg ratio. Improvements in fracture toughness and transverse-orientation properties in both alloy classes depend on improved melt practices to eliminate oxide inclusions which are incorporated into the consolidated forms.

Meschter, P. J.↗
NASA NTRS1985

Residual mechanical properties of Ti-6Al-2Sn-4Zr-2Mo after simulated Space Shuttle reentry

Oxidation and embrittlement are concerns in use of titanium foils for shielding advanced space transportation system vehicles during earth reentry. Ti-6Al-4V in 0.003 in. and 0.035 in. thicknesses were exposed to multiple cycles of simulated space transportation system ascent/reentry conditions at temperatures ranging from 1000 F to 1200 F. Residual mechanical tests and metallurgical analyses were made on the specimens after exposure. Results show that tensile elongation is the mechanical property most affected by the reentry environment. Results are presented to show a comparison of residual properties of foil specimens from static oxidation exposure and cyclic oxidation exposure.

Clark, R. K.↗
NASA NTRS1987

Adhesive evaluation of water-soluble LARC-TPI

The water-soluble polyimide, identified as TPI(MTC)/H2O, was evaluated as a high temperature thermoplastic adhesive for bonding Ti-6Al-4V and comparing those results primarily with results reported in earlier work with the polyamic-acid/diglyme material. The lap shear strength test was the primary test performed to evaluate the adhesive before (controls) and after thermal exposure in air at 204 C for up to 5000 hours and after a 72 hour water-boil exposure. Lap shear strengths were determined at RT, 177, 204, and 232 C. The adhesive was also characterized after fracture by determining the glass transition temperature as well as defining the mode of failure by visual observation. In general, the results indicate that the TPI(MTC)/H2O retains high lap shear strengths after thermal exposure but had reduced strengths after the water-boil exposure. All failures were cohesive. The TPI(MTC)/H2O compared very well with previous data reported for the standard polyamic-acid/diglyme LARC-TPI results, and therefore, shows promise as a water-soluble adhesive for use in various applications.

Progar, Donald J.↗
NASA NTRS1988

Initial adhesive screening of novel polyamide-imides and their copolymers

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Donald J Progar↗
NASA NTRS1987

Evaluation of polyimide films as adhesives

A commercially available LARC-TPI film and an experimentally prepared film of LARC-TPI with 5 mol pct of 4,4-prime-oxydianiline (ODA), designated as LARC-TPI/ODA, were evaluated as thermoplastic adhesive films for bonding Ti-6Al-4V. Lap shear strength was used to evaluate the materials as adhesives. They were characterized after fracture by determining the glass transition temperature, T(g). The mode of failure is also reported. Thermal exposure at 240 C for 500 and 1000 h and a 72-h water-boil were conducted on lap shear specimens prepared with the two adhesive films. Lap shear tests were conducted at room temperature, 177 C, 204 C, and 232 C before and after exposures.

Progar, Donald J.↗
NASA NTRS1988

Adhesive evaluation of water-soluble LARC-TPI

The water-soluble polyimide, identified as TPI(MTC)/H2O, was evaluated as a high temperature thermoplastic adhesive for bonding Ti-6Al-4V and comparing those results primarily with results reported in earlier work with the polyamic-acid/diglyme material. The lap shear strength test was the primary test performed to evaluate the adhesive before (controls) and after thermal exposure in air at 204 C for up to 5000 hours and after a 72 hour water-boil exposure. Lap shear strengths were determined at RT, 177, 204, and 232 C. The adhesive was also characterized after fracture by determining the glass transition temperature as well as defining the mode of failure by visual observation. In general, the results indicate that the TPI(MTC)/H2O retains high lap shear strengths after thermal exposure but had reduced strengths after the water-boil exposure. All failures were cohesive. The TPI(MTC)/H2O compared very well with previous data reported for the standard polyamic-acid/diglyme LARC-TPI results, and therefore, shows promise as a water-soluble adhesive for use in various applications.

Progar, D. J.↗
NASA NTRS1988

Strain measurement technique for elevated temperature tensile and creep testing of foil-gage metals

This paper describes a strain measurement technique suitable for elevated-temperature tensile and creep testing of foil-gage metals, using a modified commonly available mechanical extensometer in conjunction with a displacement transducer. The extensometer was modified by attaching to it a counterbalance (to reduce the effect of the extensometer weight on the total maximum test load) and by incorporating a conical tip/flat-edge design (to minimize induced stresses in the specimen resulting from extensometer attachment). Creep tests were performed on 0.102-mm-thick specimens of Ti-6Al-4V at temperatures of 427 and 538 C, at nominal applied stresses of 310.3 and 172.4 MPa, respectively. Examination of the resulting creep curves suggested that the strain measurement system provided actual creep strain values with good accuracy.

Blackburn, L. B.↗
NASA NTRS1989

Rapidly solidified titanium alloys by melt overflow

A pilot plant scale furnace was designed and constructed for casting titanium alloy strips. The furnace combines plasma arc skull melting techniques with melt overflow rapid solidification technology. A mathematical model of the melting and casting process was developed. The furnace cast strip of a suitable length and width for use with honeycomb structures. Titanium alloys Ti-6Al-4V and Ti-14Al-21 Nb were successfully cast into strips. The strips were evaluated by optical metallography, microhardness measurements, chemical analysis, and cold rolling.

Gaspar, Thomas A.↗
NASA NTRS1989

Initial evaluation of novel polyamide-imides and their copolymers as adhesives

Continued interest by the research community in thermally stable, tough, high temperature adhesives has resulted in the investigation by Langley Research Center of two linear aromatic polyamide-imide (PAI) homopolymers and two linear aromatic PAI copolymers. The homopolymers were made with either 3,3'=DABA or 4,4'-DABA and BTDA. The two polymers were prepared with a monomer ratio of 0.75 DABP:0.25 DABA:1.00 BTDA. These aromatic PAIs possess high thermal stability because of intermolecular hydrogen bonding and chain stiffness. Lap shear strength (LSS) was the main criteria used to evaluate the polymers as adhesives. LSS of bonded Ti-6Al-4V was determined at room temperature (RT), 177, 204 and 232 C. The glass transition temperature and the type of bond failure were also determined. The best LSS values of the four adhesive systems investigated were obtained with the PAI copolymer identified in the report as LARC-TPI (25 percent 3,3'-DABA); however, it did not produce LSSs nearly as high as LARC-TPI. The poor flow properties observed appear to be due to a combination of high molecular weight and the increased interchain electronic interactions associated with the amide group.

Progar, Donald J.↗
NASA NTRS1992

Fatigue mechanics - An assessment of a unified approach to life prediction

Consideration is given to the development of a total-life prediction methodology for aerospace structures based solely on crack propagation from a microstructural defect at stress concentrations. Crack-growth lives were calculated for a given loading condition by integrating the crack-growth-rate-against-delta K relationships for crack growth from a microstructural defect size to failure. Both small- and large-crack growth rate data were used. The assessment was based on data on 2024-T3 aluminum alloy, 2090-T8E41 aluminum-lithium alloy, annealed Ti-6Al-4V titanium alloy, and high-strength 4340 steel under either constant-amplitude or spectrum loading. Good agreement was found between fatigue lives measured on notched specimens with those computed from the total-life analysis.

Newman, J. C., Jr.↗
NASA NTRS1993

The Corrosion Protection of Metals by Ion Vapor Deposited Aluminum

A study of the corrosion protection of substrate metals by ion vapor deposited aluminum (IVD Al) coats has been carried out. Corrosion protection by both anodized and unanodized IVD Al coats has been investigated. Base metals included in the study were 2219-T87 Al, 7075-T6 Al, Titanium-6 Al-4 Vanadium (Ti-6Al-4V), 4130 steel, D6AC steel, and 4340 steel. Results reveal that the anodized IVD Al coats provide excellent corrosion protection, but good protection is also achieved by IVD Al coats that have not been anodized.

Danford, M. D.↗
NASA NTRS1994

A new stochastic systems approach to structural integrity

This paper develops improved stochastic models for the description of a large variety of fatigue crack growth phenomena that occur in components of considerable importance to the functionality and reliability of complex engineering structures. In essence, the models are based on the McGill-Markov and Closure-Lognormal stochastic processes. Not only do these models have the capability of predicting the statistical dispersion of crack growth rates, they also, by incorporating the concept of crack closure, have the capability of transferring stochastic crack growth properties measured under ideal laboratory conditions to situations of industrial significance, such as those occurring under adverse loading and/or environmental conditions. The primary data required in order to be in a position to estimate the pertinent parameters of these stochastic models are obtained from a statistically significant number of replicate tests. In this paper, both the theory and the experimental technique are illustrated using a Ti-6Al-4V alloy. Finally, important structural integrity, reliability, availability and maintainability concepts are developed and illustrated.

Provan, James W.↗
NASA NTRS1995

Materials research for High Speed Civil Transport and generic hypersonics: Adhesive durability

This report covers a portion of an ongoing investigation of the durability of adhesives for the High Speed Civil Transport (HSCT) program. Candidate HSCT adhesives need to possess the high-temperature capability required for supersonic flight. This program was designed to initiate an understanding of the behavior of candidate HSCT materials when subjected to combined mechanical and thermal loads. Two adhesives (K3A and FM57) and two adherends (IM7/K3B polymeric composite and the titanium alloy Ti-6Al-4V) were used to fabricate thick adherend lap shear specimens. Due to processing problems, only the FM57/titanium bonds could be fabricated successfully. These are currently undergoing thermomechanical fatigue (TMF) testing. There is an acute need for an adhesive to secondarily bond polymeric composite adherends or, alternately, polymeric composites that remain stable at the processing temperatures of today's adhesives.

Allen, Mark R.↗
NASA NTRS1998

Simulated Bladed MMC Disk LCF Validation

The goal of this program was to evaluate the low cycle fatigue behavior of an SCS-6/Ti-6Al-4V sub-component under bi-axial loading conditions at 316 C(600 F). A simulated bladed TMC disk was designed having thirty four blades representing the number that would be used in Allied Signal's JTAGG II impeller. The outer diameter of the bladed ring was 254 mm (10.0 inch) and the inner diameter 114.3 mm (4.50 inch). The outer and inner diameter of the composite zone was 177.8 mm (7.00 inch) and 127.O mm(5.00 inch) respectively. Stress analysis showed that the fatigue life of the bladed composite ring would be about 12000 cycles for the test conditions applied. A modal analysis was conducted which showed that the blades would have sufficient life margin from dynamic excitation. The arbor design was the same as that employed in the spin-to burst test of NAS3-27027. A systematic stress analysis of each part making up the arbor was undertaken to assure the design would meet the low cycle fatigue requirements of the program. The Textron Systems grooved foil-fiber process was chosen to make the SCS-6/Ti-6Al-4V core ring based on the success they had in contract NAS3-27027. Fiber buckling, however, was observed at several locations in the first ring made which rendered it unsuitable for spin testing. The fiber buckling was attributed to cracking of the graphite tooling during the consolidation process. On this basis a second ring was made but it too contained fiber buckling defects. Analysis by Textron indicated that the fiber buckling was most likely due to poor placement of the SCS-6 fiber in the etched grooves of the Ti-6Al-4V foil. This was also a contributor to the defects in the first ring. Since there was little indication of control in the process to manufacture a quality ring a third attempt at making a ring was not undertaken.

Merrick, H. F.↗
NASA NTRS1998

TMC Behavior Modeling and Life Prediction Under Multiaxial Stresses

The goal of this program was to manufacture and burst test small diameter SCS-6/Ti-6Al-4V composite rings for use in the design of an advanced titanium matrix composite (TMC) impeller. The Textron Specialty Metals grooved foil-fiber process was successfully used to make high quality TMC rings. A novel spin test arbor with "soft touch" fingers to retain the TMC ring was designed and manufactured. The design of the arbor took into account its use for cyclic experiments as well as ring burst tests. Spin testing of the instrumented ring was performed at ambient, 149C (300F), and 316C (600F) temperatures. Assembly vibration was encountered during spin testing but this was overcome through simple modification of the arbor. A spin-to-burst test was successfully completed at 316C (600F). The rotational speed of the TMC ring at burst was close to that predicted. In addition to the spin test program, a number of SCS-6/Ti-6Al-4V test panels were made. Neat Ti-6Al-4V panels also were made.

Merrick, H. F.↗