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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

A Simplified Test for Blanching Susceptibility of Copper Alloys

GRCop-84 (Cu-8Cr-4Nb) is a dispersion-strengthened alloy developed for space-launch rocket engine applications, as a liner for the combustion chamber and nozzle ramp. Its main advantage over rival alloys, particularly NARloy-Z (Cu-Ag-Zr), the current liner alloy, is in high temperature mechanical properties. Further validation required that the two alloys be compared with respect to service performance and durability. This has been done, under conditions resembling those expected in reusable launch engine applications. GRCop-84 was found to have a superior resistance to static and cyclic oxidation up to approx. 700 C. In order to improve its performance above 700 C, Cu-Cr coatings have also been developed and evaluated. The major oxidative issue with Cu alloys is blanching, a mode of degradation induced by oxidation-reduction fluctuations in hydrogen-fueled engines. That fluctuation cannot be addressed with conventional static or cyclic oxidation testing. Hence, a further evaluation of the alloy substrates and Cu-Cr coating material necessitated our devising a test protocol that involves oxidaton-reduction cycles. This paper describes the test protocols used and the results obtained.

Thomas-Ogbuji, Linus U.↗
NASA NTRS2003

Mechanistic Studies Of Combustion And Structure Formation During Combustion Synthesis Of Advanced Materials: Phase Separation Mechanism For Bio-Alloys

Among all implant materials, Co-Cr-Mo alloys demonstrate perhaps the most useful balance of resistance to corrosion, fatigue and wear, along with strength and biocompatibility [1]. Currently, these widely used alloys are produced by conventional furnace technology. Owing to high melting points of the main alloy elements (e.g. Tm.p.(Co) ~1768 K), high-temperature furnaces and long process times (several hours) are required. Therefore, attempts to develop more efficient and flexible methods for production of such alloys with superior properties are of great interest. The synthesis of materials using combustion phenomena is an advanced approach in powder metallurgy [2]. The process is characterized by unique conditions involving extremely fast heating rates (up to 10(exp 6 K/s), high temperatures (up to 3500 K), and short reaction times (on the order of seconds). As a result, combustion synthesis (CS) offers several attractive advantages over conventional metallurgical processing and alloy development technologies. The foremost is that solely the heat of chemical reaction (instead of an external source) supplies the energy for the synthesis. Also, simple equipment, rather than energy-intensive high-temperature furnaces, is sufficient. This work was devoted to experiments on CS of Co-based alloys by utilizing thermite (metal oxide-reducing metal) reactions, where phase separation subsequently produces materials with tailored compositions and properties. Owing to high reaction exothermicity, the CS process results in a significant increase of temperature (up to 3000 C), which is higher than melting points of all products. Since the products differ in density, phase separation may be a gravitydriven process: the heavy (metallic phase) settles while the light (slag) phase floats. The goal was to determine if buoyancy is indeed the major mechanism that controls phase segregation.

Varma, A.↗
NASA NTRS2004

Microstructural Evaluations of Baseline HSR/EPM Disk Alloys

Six alloys representing two classes of powder metallurgy nickel-based superalloys were examined by transmission electron microscopy (TEM) and phase extraction. Alloys KM4, CH98, IN-100 and 456 are based on a Ni-18Co-12Cr composition while alloys Rene' 88 DT and SR 3 have lower Al and Co and higher Cr contents. The lambda size distributions were determined from quantitative image analysis of the TEM images. The volume fraction of lambda and carbides and the composition of the phases were determined by a combination of phase extraction and TEM. The results showed many similarities in lambda size distributions, grain boundary serrations, and grain boundary carbide frequencies between alloys KM4, CH98, 456, Rene' 88 DT and SR 3 when heat treated to give an approximate grain size of ASTM 6. The density of grain boundary carbides in KM4 was shown to substantially increase as the grain size increased. IN-100 and 456 subjected to a serration cooling heat treatment had much more complex lambda size distributions with very large intergranular and intragranular secondary lambda as well as finer than average cooling and aging lambda. The grain boundary carbides in IN-100 were similar to the other alloys, but 456 given the serration cooling heat treatment had a more variable density of grain boundary carbides. Examination of the phases extracted from the matrix showed that there were significant differences in the phase chemistries and elemental partitioning ratios between the various alloys.

Gabb, Timothy P.↗
NASA NTRS1996

New Theoretical Technique Developed for Predicting the Stability of Alloys

When alloys are being designed for aeronautical and other applications, a substantial experimental effort is necessary to make incremental changes in the desired alloy properties. A scheme to narrow the field to the most promising candidates would substantially reduce the high cost of this experimental screening. Such a method for determining alloy properties, called the BFS (Bozzolo, Ferrante, and Smith) method, has been developed at the NASA Lewis Research Center. This method was used to calculate the thermal stability and mechanical strength of 200 alloys of Ni3Al, with Cu and Au impurities forming ternary and quaternary compounds. With recent advances in the method, almost any metallic impurity and crystal structure can be addressed. In addition, thermal effects can be addressed with Monte Carlo techniques. At present, an experimental program is in progress to verify these results. The method identified a small number of the most promising candidates from the 200 alloys with the largest negative heat of formation and the highest bulk modulus. This calculation required only 5 min of CPU time on a VAX computer. It is clear that semi-empirical methods have achieved the level of development and reliability to warrant examining this new approach to the problem of alloy design. The present work was meant to demonstrate, perhaps in a rather simple way, this power. This type of application of atomistic simulation methods can narrow the gap and improve the feedback between theoretical predictions and laboratory experimentation.

Source record↗
NASA NTRS1997

BFS Method for Alloys Optimized and Verified for the Study of Ordered Intermetallic Material

The aerospace industry has a need for new metallic alloys that are lightweight and have high strength at elevated temperatures. The BFS (Bozzolo, Ferrante, and Smith) method is a new, computationally efficient and physically sound quantum semi-perturbative approach for describing metals and their defects. Based on a simple interpretation of the alloy formation process that identifies strain and chemical contributions to the energy of the alloy, the method provides an atom-by-atom description of an alloy. Its implementation requires little more than algebra and the solution of transcendental equations. At the NASA Lewis Research Center, we have demonstrated that BFS can investigate the properties of a large number of alloys with a minimum computational effort on low-level computers. This screening allows the selection of the best alloy candidates for a particular application and, therefore, promises large cost savings over current approaches.

Source record↗
NASA NTRS2004

Potential High-Temperature Shape-Memory Alloys Identified in the Ti(Ni,Pt) System

"Shape memory" is a unique property of certain alloys that, when deformed (within certain strain limits) at low temperatures, will remember and recover to their original predeformed shape upon heating. It occurs when an alloy is deformed in the low-temperature martensitic phase and is then heated above its transformation temperature back to an austenitic state. As the material passes through this solid-state phase transformation on heating, it also recovers its original shape. This behavior is widely exploited, near room temperature, in commercially available NiTi alloys for connectors, couplings, valves, actuators, stents, and other medical and dental devices. In addition, there are limitless applications in the aerospace, automotive, chemical processing, and many other industries for materials that exhibit this type of shape-memory behavior at higher temperatures. But for high temperatures, there are currently no commercial shape-memory alloys. Although there are significant challenges to the development of high-temperature shape-memory alloys, at the NASA Glenn Research Center we have identified a series of alloy compositions in the Ti-Ni-Pt system that show great promise as potential high-temperature shape-memory materials.

Noebe, Ronald D.↗
NASA NTRS2004

Compatibility of Niobium Alloys and Superalloys in a Flowing He-Xe Power Conversion System

Proposed concepts for an ambitious mission to explore Jupiter's three icy moons place significant demands on the various spacecraft systems. There are many challenges related to the high output power conversion systems being considered, and one example is the need to ensure system compatibility at all levels. The utilization of appropriate materials for component structures is important to ensuring long mission life. Refractory metal alloys have attractive high-temperature properties in inert environments, but these alloys are sometimes susceptible to contamination. Potential material compatibility issues exist between refractory metal candidates and more conventional alloys. Nb-1Zr has long been considered one of the most well characterized refractory alloys that is well suited for elevated-temperature use and liquid-metal compatibility. However, previous studies have suggested that niobium alloys can not co-exist in a closed system with traditional stainless steels or superalloys due to transport of contaminants. The relevance of this information to a proposed power conversion system is discussed. Also, experiments and fundamental calculations are being performed to determine contamination transport from candidate superalloys to Nb-1Zr in a closed system with an inert carrier gas. Potential protective schemes are explored to ensure system level compatibility between the refractory alloy Nb-1Zr and a nickel-based superalloy.

Bowman, Cheryl L.↗
NASA NTRS2001

Disk Alloy Development

The advanced powder metallurgy disk alloy ME3 was designed using statistical screening and optimization of composition and processing variables in the NASA HSR/EPM disk program to have extended durability at 1150 to 1250 "Fin large disks. Scaled-up disks of this alloy were produced at the conclusion of this program to demonstrate these properties in realistic disk shapes. The objective of the UEET disk program was to assess the mechanical properties of these ME3 disks as functions of temperature, in order to estimate the maximum temperature capabilities of this advanced alloy. Scaled-up disks processed in the HSR/EPM Compressor / Turbine Disk program were sectioned, machined into specimens, and tested in tensile, creep, fatigue, and fatigue crack growth tests by NASA Glenn Research Center, in cooperation with General Electric Engine Company and Pratt & Whitney Aircraft Engines. Additional sub-scale disks and blanks were processed and tested to explore the effects of several processing variations on mechanical properties. Scaled-up disks of an advanced regional disk alloy, Alloy 10, were used to evaluate dual microstructure heat treatments. This allowed demonstration of an improved balance of properties in disks with higher strength and fatigue resistance in the bores and higher creep and dwell fatigue crack growth resistance in the rims. Results indicate the baseline ME3 alloy and process has 1300 to 1350 O F temperature capabilities, dependent on detailed disk and engine design property requirements. Chemistry and process enhancements show promise for further increasing temperature capabilities.

Gabb, Tim↗
NASA NTRS2006

Observations of a Cast Cu-Cr-Zr Alloy

Prior work has demonstrated that Cu-Cr-Nb alloys have considerable advantages over the copper alloys currently used in regeneratively cooled rocket engine liners. Observations indicated that Zr and Nb have similar chemical properties and form very similar compounds. Glazov and Zakharov et al. reported the presence of Cr2Zr in Cu-Cr-Zr alloys with up to 3.5 wt% Cr and Zr though Zeng et al. calculated that Cr2Zr could not exist in a ternary Cu-Cr-Zr alloy. A cast Cu-6.15 wt% Cr-5.25 wt% Zr alloy was examined to determine if the microstructure developed would be similar to GRCop-84 (Cu-6.65 wt% Cr-5.85 wt% Nb). It was observed that the Cu-Cr-Zr system did not form any Cr2Zr even after a thermal exposure at 875 C for 176.5 h. Instead the alloy consisted of three phases: Cu, Cu5Zr, and Cr.

Ellis, David L.↗
NASA NTRS2007

Development and Processing Improvement of Aerospace Aluminum Alloys

This final report, in multiple presentation format, describes a comprehensive multi-tasked contract study to improve the overall property response of selected aerospace alloys, explore further a newly-developed and registered alloy, and correlate the processing, metallurgical structure, and subsequent properties achieved with particular emphasis on the crystallographic orientation texture developed. Modifications to plate processing, specifically hot rolling practices, were evaluated for Al-Li alloys 2195 and 2297, for the recently registered Al-Cu-Ag alloy, 2139, and for the Al-Zn-Mg-Cu alloy, 7050. For all of the alloys evaluated, the processing modifications resulted in significant improvements in mechanical properties. Analyses also resulted in an enhanced understanding of the correlation of processing, crystallographic texture, and mechanical properties.

Lisagor, W. Barry↗
NASA NTRS2008

Durability Assessment of TiAl Alloys

The durability of TiAl is a prime concern for the implementation of TiAl into aerospace engines. Two durability issues, the effect of high temperature exposure on mechanical properties and impact resistance, have been investigated and the results are summarized in this paper. Exposure to elevated temperatures has been shown to be detrimental to the room temperature ductility of gamma alloys with the most likely mechanisms being the ingress of interstitials from the surface. Fluorine ion implantation has been shown to improve the oxidation resistance of gamma alloys, and ideally it could also improve the environmental embrittlement of high Nb content TiAl alloys. The effect of F ion implantation on the surface oxidation and embrittlement of a third generation, high Nb content TiAl alloy (Ti-45Al-5Nb-B-C) were investigated. Additionally, the ballistic impact resistance of a variety of gamma alloys, including Ti-48Al-2Cr- 2Nb, Ti-47Al-2Cr-2Nb, ABB-2, ABB-23, NCG359E, 95A and Ti-45Al-5Nb-B-C was accessed. Differences in the ballistic impact properties of the various alloys will be discussed, particularly with respect to their manufacturing process, microstructure, and tensile properties.

Draper, Susan L.↗
NASA NTRS2008

Characterization of a New Phase and Its Effect on the Work Characteristics of a Near-Stoichiometric Ni30Pt20Ti50 High-Temperature Shape Memory Alloy (HTSMA)

A new phase observed in a nominal Ni30Pt20Ti50 (at.%) high temperature shape memory alloy has been characterized using transmission electron microscopy and 3-D atom probe tomography. This phase forms homogeneously in the B2 austenite matrix by a nucleation and growth mechanism and results in a concomitant increase in the martensitic transformation temperature of the base alloy. Although the structure of this phase typically contains a high density of faults making characterization difficult, it appears to be trigonal (-3m point group) with a(sub o) approx. 1.28 nm and c(sub o) approx. 1.4 nm. Precipitation of this phase increases the microhardness of the alloy substantially over that of the solution treated and quenched single-phase material. The effect of precipitation strengthening on the work characteristics of the alloy has been explored through load-biased strain-temperature testing in the solution-treated condition and after aging at 500 C for times ranging from 1 to 256 hours. Work output was found to increase in the aged alloy as a result of an increase in transformation strain, but was not very sensitive to aging time. The amount of permanent deformation that occurred during thermal cycling under load was small but increased with increasing aging time and stress. Nevertheless, the dimensional stability of the alloy at short aging times (1-4 hours) was still very good making it a potentially useful material for high-temperature actuator applications.

Garg, A.↗
NASA NTRS2008

Nanophase Nickel-Zirconium Alloys for Fuel Cells

Nanophase nickel-zirconium alloys have been investigated for use as electrically conductive coatings and catalyst supports in fuel cells. Heretofore, noble metals have been used because they resist corrosion in the harsh, acidic fuel cell interior environments. However, the high cost of noble metals has prompted a search for less-costly substitutes. Nickel-zirconium alloys belong to a class of base metal alloys formed from transition elements of widely different d-electron configurations. These alloys generally exhibit unique physical, chemical, and metallurgical properties that can include corrosion resistance. Inasmuch as corrosion is accelerated by free-energy differences between bulk material and grain boundaries, it was conjectured that amorphous (glassy) and nanophase forms of these alloys could offer the desired corrosion resistance. For experiments to test the conjecture, thin alloy films containing various proportions of nickel and zirconium were deposited by magnetron and radiofrequency co-sputtering of nickel and zirconium. The results of x-ray diffraction studies of the deposited films suggested that the films had a nanophase and nearly amorphous character.

Narayanan, Sekharipuram↗
NASA NTRS2009

Zinc Alloys for the Fabrication of Semiconductor Devices

ZnBeO and ZnCdSeO alloys have been disclosed as materials for the improvement in performance, function, and capability of semiconductor devices. The alloys can be used alone or in combination to form active photonic layers that can emit over a range of wavelength values. Materials with both larger and smaller band gaps would allow for the fabrication of semiconductor heterostructures that have increased function in the ultraviolet (UV) region of the spectrum. ZnO is a wide band-gap material possessing good radiation-resistance properties. It is desirable to modify the energy band gap of ZnO to smaller values than that for ZnO and to larger values than that for ZnO for use in semiconductor devices. A material with band gap energy larger than that of ZnO would allow for the emission at shorter wavelengths for LED (light emitting diode) and LD (laser diode) devices, while a material with band gap energy smaller than that of ZnO would allow for emission at longer wavelengths for LED and LD devices. The amount of Be in the ZnBeO alloy system can be varied to increase the energy bandgap of ZnO to values larger than that of ZnO. The amount of Cd and Se in the ZnCdSeO alloy system can be varied to decrease the energy band gap of ZnO to values smaller than that of ZnO. Each alloy formed can be undoped or can be p-type doped using selected dopant elements, or can be n-type doped using selected dopant elements. The layers and structures formed with both the ZnBeO and ZnCdSeO semiconductor alloys - including undoped, p-type-doped, and n-type-doped types - can be used for fabricating photonic and electronic semiconductor devices for use in photonic and electronic applications. These devices can be used in LEDs, LDs, FETs (field effect transistors), PN junctions, PIN junctions, Schottky barrier diodes, UV detectors and transmitters, and transistors and transparent transistors. They also can be used in applications for lightemitting display, backlighting for displays, UV and visible transmitters and detectors, high-frequency radar, biomedical imaging, chemical compound identification, molecular identification and structure, gas sensors, imaging systems, and for the fundamental studies of atoms, molecules, gases, vapors, and solids.

Ryu, Yungryel↗
NASA NTRS1960

The Influence of Silicon Additions on Friction and Wear of Nickel Alloys at Temperatures to 1000 Degrees Fahrenheit

Small additions of silicon have considerable beneficial effect on performance on slider alloys. This effect has most frequently been attributed to increased hardness. The research reported was conducted to consider a hypothesis that the primary role of silicon in slider alloys is one of supporting the formation of protective surface films. Friction and wear data were obtained at temperatures from 75 to 1000 degrees Fahrenheit with a series of binary silicon-nickel alloys containing up to 10 percent silicon. Pertinent hot hardness, metallurgical and surface-film analysis data are included. Atmospheres used were air, mixtures of oxygen and argon, a mixture of hydrogen and nitrogen, and a halogenated methane gas lubricant. The results show the role of silicon as a film former to be of great importance in success of silicon-containing alloys as slider materials for extreme temperatures. The range of variables studied gave friction coefficients from 0.05 to greater than 10.00 depending on film formation tendencies. Alloys with 5 percent or more silicon having a duplex structure showed the best results. Film formation resulted from surface reactions or the smearing of the softer phase from the alloys having duplex structure.

Buckley, Donald H.↗
NASA NTRS2016

NiTi Alloys for Tribological Applications: The Role of In-Situ Nanotechnology

Beginning in 2004, NASA initiated the investigation and development of, Nitinol 60, a nickel-rich and dimensionally stable version of shape memory alloy Nitinol 55, as an alternative to bearing steel. Early investigations showed it to be hard and impervious to aqueous corrosion but the fundamental reasons for these properties were unknown. Shape memory alloys made from equiatomic Ni-Ti are widely known for their unique dimensional instability behavior that can be triggered by thermal and mechanical stress. The nickel-rich alloys exhibit no such dimension change property and have high hardness but have largely been overlooked by industry and the engineering community. Though steel is the dominant material of choice for mechanical components (bearings and gears) it has intrinsic limitations related to corrosion and plastic deformation. In contrast, Ni-Ti alloys are intrinsically rustproof and can withstand high contact loads without damage (denting). Over the last decade, focused RD to exploit these alloys for new applications has revealed that in-situ nano-scale phases that form during processing are largely responsible for NiTis remarkable properties. In this presentation, the state-of-art of nickel-rich NiTi alloys will be introduced and the nanotechnology behind their intriguing behavior will be addressed. The presentation will include discussion of how NASA is adopting this new technology inside the space station water recycling system as a pathfinder for more down-to-earth tribological challenges.

metals↗
NASA NTRS2018

Nickel Titanium Alloys, Methods of Manufacture Thereof and Article Comprising the Same

Disclosed herein is a shape memory alloy comprising 48 to 50 atomic percent nickel, 15 to 30 atomic percent hathium, 1 to 5 atomic percent aluminum; with the remainder being titanium. Disclosed herein too is a method of manufacturing a shape memory alloy comprising mixing together to form an alloy nickel, hafnium, aluminum and titanium in amounts of 48 to 50 atomic percent nickel, 15 to 30 atomic percent hafnium, 1 to 5 atomic percent aluminum; with the remainder being titanium; solution treating the alloy at a temperature of 700 to 1300.degree. C. for 50 to 200 hours; and aging the alloy at a temperature of 400 to 800.degree. C. for a time period of 50 to 200 hours to form a shape memory alloy.

Manuel, Michele Viola↗
NASA NTRS2019

Fatigue Behavior of Coated Titanium Alloys

Advanced multi-component TiAlCrTaSiN-based multilayered coatings were developed and processed onto Ti-6Al-4V (Ti-6-4) and GammaMet PX (GMPX or TiAl) alloys by a magnetron-enhanced physical vapor deposition technique. The coatings have recently been in development with the goal of improving advanced titanium alloy, turbine engine component durability and oxidation-erosion resistance. In this work, the performance of the multi-component coating system (including the outer layer nitride based coating and inner TiAlCrSi oxidation barrier bond coat) was studied, and the coating's influence on the fatigue behavior of the titanium-based alloys were compared. Although the multi-component coating was initially optimized to improve the coating's high temperature oxidation and erosion resistance, the lower ductility nitride-based coating needs further work on microstructure or composition to improve its mechanical stress resistance and strain tolerance for use in cyclically loaded, turbine blade operating conditions. This is particularly true for GMPX and other γ-TiAl alloys because these intermetallic titanium alloys have limited ductility and are very sensitive to defects such as coating cracks. However, the inner layer TiAlCrSi-coating had better adhesion and ductility, and may be a suitable choice to improve the oxidation resistance of titanium alloys.

Oxidation Barrier Coatings↗