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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Characteristics of an Elevated Temperature ALN Particulate Reinforced NiAl

High energy milling of NiAl in liquid nitrogen (cryomilling) leads to the formation of a discontinuously AlN particle reinforced aluminide which has shown good potential as a high strength oxidation resistant material. Experiments have demonstrated that cryomilling is repeatable, and materials with reproducible chemistries and mechanical properties result. Furthermore, it is possible to vary the AlN content through control of the milling parameters. Tensile creep as well as compressive creep testing has been undertaken on a lot of NiAl-AlN. While this material is weaker in tension than compression, the tensile strength is respectable: for example, the creep rupture life exceeds 2700 h at 1300 K, 50 MPa. Heat treatment of the particulate reinforced aluminide at 1600 K promotes AlN growth which weakens the material but does not change the deformation mechanism. Cyclic oxidation testing of lots of NiAl-AlN which were cryomilled with and without yttria reveal that Y2O3 promotes better oxidation resistance. However, the presence or absence of yttria had no affect on the mechanical properties.

Whittenberger, J. D.↗
NASA NTRS2002

Three-Dimensional Stress Fields and Slip Systems for Single Crystal Superalloy Notched Specimens

Single crystal superalloys have become increasingly popular for turbine blade and vane applications due to their high strength, and creep and fatigue resistance at elevated temperatures. The crystallographic orientation of a single crystal material greatly affects its material properties, including elastic modulus, shear modulus, and ductility. These directional properties, along with the type of loading and temperature, dictate an anisotropic response in the yield strength, creep resistance, creep rupture ductility, fatigue resistance, etc. A significant amount of research has been conducted to determine the material properties in the <001> orientation, yet the material properties deviating from the <001> orientation have not been assessed for all cases. Based on the desired application and design criteria, a crystal orientation is selected to yield the maximum properties. Currently, single crystal manufacturing is able to control the primary crystallographic orientation within 15 of the target orientation, which is an acceptable deviation to meet both performance and cost guidelines; the secondary orientation is rarely specified. A common experiment is the standard load-controlled tensile test, in which specimens with different orientations can be loaded to observe the material response. The deformation behavior of single-crystal materials under tension and compression is known to be a function of not only material orientation, but also of varying microdeformation (i.e. dislocation) mechanisms. The underlying dislocation motion causes deformation via slip, and affects the activation of specific slip systems based on load and orientation. The slip can be analyzed by observing the visible traces left on the surface of the specimen from the slip activity within the single crystal material. The goal of this thesis was to predict the slip systems activated in three-dimensional stress fields of a notched tensile specimen, as a function of crystal orientation, using finite element analysis without addressing microstructural deformation mechanisms that govern their activation. Out of three orientations tested, the specimen with a [110] load orientation and a [001] growth direction had the lowest maximum resolved shear stress; this specimen orientation appears to be the best design candidate for a tensile application.

Magnan, Shannon M.↗
NASA NTRS2004

Goals and Progress for Mil Handbook 17, Vol. 5 on Ceramic Matrix Composites: Testing and Characterization

The initial edition of the Mil Handbook 17, Vol. 5 on ceramic matrix composites (CMCs) was recently published. Part C of this CMC volume describes procedures for characterization of the thermal, physical, and mechanical properties of CMCs and subsequent data analysis procedures. As is the case for entire CMC volume, this chapter is a "work in progress" with sections on recommended test plans and matrices, data reduction, and test methods. This presentation will describe the current status in development of this section of the CMC volume and will highlight examples of critical issues that will be addressed in this volume. CMC systems are a different class of material than metals or polymer matrix composite with different mechanical response and failure modes, design rules, test methods, and characterization techniques. The CMC test protocols need to include guidance on how to generate enough reliable data in order to estimate, with reasonable confidence, the lower bounds of performance properties, such as strength and life. Strength data sets on two material systems, C/SiC and Nicalon/SiNC, and a creep rupture data set on C/SiC, will be presented to highlight this issue. The structural properties of CMC parts can sometimes be significantly different than those obtained from flat panels because of changes in fiber architecture often required to make shapes and spatial and lot-to-lot variations in processing conditions. To illustrate an example, the hoop tensile properties of SiC/SiC cylinders will be compared to properties obtained from flat panels fabricated from the same composites. These CMC testing-design issues are being defined and documented in the Mil Handbook 17 CMC volume.

Verrilli, Michael J.↗
NASA NTRS2004

SiC/SiC Composites for Applications Above 2600 F

Using data from panels with 2D woven architectures,t his presentation describes progress in identifying advanced constituent materials and processes for achieving a high conductivity SiC/SiC composite system with long-term structural life under oxidizing conditions at 2600 degrees F. A key factor for this progress is the development of approaches at NASA GRC that allow the constituent SiC fiber and SiC matrix to display high thermal conductivity, high creep-rupture resistance and high microstructural stability at temperatures above 3000 degree F. Another important factor is the avoidance of free silicon in the SiC matrix, thereby providing the composites with the capability for extended service above the silicon melting point (2550 degrees F). The effects of utilizing various materials and processes for the SiC matrix are presented and discussed.

DiCarlo, James A.↗
NASA NTRS2004

Joint Development of a Fourth Generation Single Crystal Superalloy

A new, fourth generation, single crystal superalloy has been jointly developed by GE Aircraft Engines, Pratt & Whitney, and NASA. The focus of the effort was to develop a turbine airfoil alloy with long-term durability for use in the High Speed Civil Transport. In order to achieve adequate long-time strength improvements at moderate temperatures and retain good microstructural stability, it was necessary to make significant composition changes from 2nd and 3rd generation single crystal superalloys. These included lower chromium levels, higher cobalt and rhenium levels and the inclusion of a new alloying element, ruthenium. It was found that higher Co levels were beneficial to reducing both TCP precipitation and SRZ formation. Ruthenium caused the refractory elements to partition more strongly to the ' phase, which resulted in better overall alloy stability. The final alloy, EPM 102, had significant creep rupture and fatigue improvements over the baseline production alloys and had acceptable microstructural stability. The alloy is currently being engine tested and evaluated for advanced engine applications.

Walston, S.↗
NASA NTRS2004

High-Performance SiC/SiC Ceramic Composite Systems Developed for 1315 C (2400 F) Engine Components

As structural materials for hot-section components in advanced aerospace and land-based gas turbine engines, silicon carbide (SiC) ceramic matrix composites reinforced by high performance SiC fibers offer a variety of performance advantages over current bill-of-materials, such as nickel-based superalloys. These advantages are based on the SiC/SiC composites displaying higher temperature capability for a given structural load, lower density (approximately 30- to 50-percent metal density), and lower thermal expansion. These properties should, in turn, result in many important engine benefits, such as reduced component cooling air requirements, simpler component design, reduced support structure weight, improved fuel efficiency, reduced emissions, higher blade frequencies, reduced blade clearances, and higher thrust. Under the NASA Ultra-Efficient Engine Technology (UEET) Project, much progress has been made at the NASA Glenn Research Center in identifying and optimizing two highperformance SiC/SiC composite systems. The table compares typical properties of oxide/oxide panels and SiC/SiC panels formed by the random stacking of balanced 0 degrees/90 degrees fabric pieces reinforced by the indicated fiber types. The Glenn SiC/SiC systems A and B (shaded area of the table) were reinforced by the Sylramic-iBN SiC fiber, which was produced at Glenn by thermal treatment of the commercial Sylramic SiC fiber (Dow Corning, Midland, MI; ref. 2). The treatment process (1) removes boron from the Sylramic fiber, thereby improving fiber creep, rupture, and oxidation resistance and (2) allows the boron to react with nitrogen to form a thin in situ grown BN coating on the fiber surface, thereby providing an oxidation-resistant buffer layer between contacting fibers in the fabric and the final composite. The fabric stacks for all SiC/SiC panels were provided to GE Power Systems Composites for chemical vapor infiltration of Glenn designed BN fiber coatings and conventional SiC matrices. Composite panels with system B were heat treated at Glenn, and the pores that remained open were filled by silicon melt infiltration (MI). Panels with system A and the other SiC/SiC systems were not heat treated, and remaining open pores in these systems were filled with SiC slurry and silicon MI.

DiCarlo, James A.↗
NASA NTRS2003

Fabrication And Evaluation Of Sic/Sic Tubes With Various Fiber Architectures

SiC/SiC composites are excellent material candidates for high temperature applications where the performance requirements are high strength, high creep-rupture resistance, high environmental durability, and high thermal conductivity. In the past, the NASA UEET program has demonstrated fabrication of high-performance SiC/SiC flat panels reinforced by Sylramic-iBN SiC fibers. Currently NASA UEET is scaling up this SiC/SiC system by fabrication of more complex shaped components using the same fiber type. This paper reports the effects of various fiber architectures on the processing, mechanical, and durability behavior of small-diameter 0.5" ID SiC/SiC tubes, which are potential sub-elements for leading edges and cooling channels in turbine vanes and blades. Nine different fiber architectures were utilized for construction of seamless tube preforms, from simple 2D jelly-rolling to complex braiding, pin-weaving, filament-winding and 3D orthogonal weaving with approximately 5% fibers in the thru-thickness direction. Using the BN interphase and Sic matrix processing steps established for the flat panels, SiC/SiC tubes were fabricated with wall thicknesses of approximately 60 mils and total fiber fractions of approximately 35%. The "D" split ring tests for hoop tensile properties, micro-structural examinations for relationship between fiber architecture formation and matrix infiltration, and the low-pressure burner rig tests for the high temperature durability under thru-thickness thermal gradient were conducted. The better matrix infiltration and higher hoop strength were achieved using the tri-axial braided and the three-float pin woven SiC/SiC tubes. In general, it needs not only higher hoop direction fibers but also axial direction fibers for the higher hoop strength and the better infiltration, respectively. These results are analyzed to offer general guidelines for selecting fiber pre-form architectures and SiC/SiC processes that maximize tube hoop strength, thru-thickness thermal conductivity, and burner-rig durability under a high thermal gradient.

Yun, H. M.↗
NASA NTRS2001

Turbine Blade Alloy

The High Speed Research Airfoil Alloy Program developed a fourth-generation alloy with up to an +85 F increase in creep rupture capability over current production airfoil alloys. Since improved strength is typically obtained when the limits of microstructural stability are exceeded slightly, it is not surprising that this alloy has a tendency to exhibit microstructural instabilities after high temperature exposures. This presentation will discuss recent results obtained on coated fourth-generation alloys for subsonic turbine blade applications under the NASA Ultra-Efficient Engine Technology (UEET) Program. Progress made in reducing microstructural instabilities in these alloys will be presented. In addition, plans will be presented for advanced alloy development and for computational modeling, which will aid future alloy development efforts.

MacKay, Rebecca↗
NASA NTRS2011

Damage Characterization in SiC/SiC Composites using Electrical Resistance

SiC/SiC ceramic matrix composites (CMCs) under creep-rupture loading accumulate damage by means of local matrix cracks that typically form near a stress concentration, such as a 90o fiber tow or large matrix pore, and grow over time. Such damage is difficult to detect through conventional techniques. Electrical resistance changes can be correlated with matrix cracking to provide a means of damage detection. Sylramic-iBN fiber-reinforced SiC composites with both melt infiltrated (MI) and chemical vapor infiltrated (CVI) matrix types are compared here. Results for both systems exhibit an increase in resistance prior to fracture, which can be detected either in situ or post-damage.

Smith, Craig E.↗
NASA NTRS2011

Factors Influencing Dwell Fatigue Cracking in Notches of Powder Metallurgy Superalloys

The influences of heat treatment and cyclic dwells on the notch fatigue resistance of powder metallurgy disk superalloys were investigated for low solvus high refractory (LSHR) and ME3 disk alloys. Disks were processed to produce material conditions with varied microstructures and associated mechanical properties. Notched specimens were first subjected to baseline dwell fatigue cycles having a dwell at maximum load, as well as tensile, stress relaxation, creep rupture, and dwell fatigue crack growth tests at 704 C. Several material heat treatments displayed a bimodal distribution of fatigue life with the lives varying by two orders-of-magnitude, while others had more consistent fatigue lives. This response was compared to other mechanical properties, in search of correlations. The wide scatter in baseline dwell fatigue life was observed only for material conditions resistant to stress relaxation. For selected materials and conditions, additional tests were then performed with the dwells shifted in part or in total to minimum tensile load. The tests performed with dwells at minimum load exhibited lower fatigue lives than max dwell tests, and also exhibited early crack initiation and a substantial increase in the number of initiation sites. These results could be explained in part by modeling evolution of peak stresses in the notch with continued dwell fatigue cycling. Fatigue-environment interactions were determined to limit life for the fatigue cycles with dwells.

Gabb, T. P.↗
NASA NTRS2016

Hydrogen Embrittlement

Hydrogen embrittlement (HE) is a process resulting in a decrease in the fracture toughness or ductility of a metal due to the presence of atomic hydrogen. In addition to pure hydrogen gas as a direct source for the absorption of atomic hydrogen, the damaging effect can manifest itself from other hydrogen-containing gas species such as hydrogen sulfide (H2S), hydrogen chloride (HCl), and hydrogen bromide (HBr) environments. It has been known that H2S environment may result in a much more severe condition of embrittlement than pure hydrogen gas (H2) for certain types of alloys at similar conditions of stress and gas pressure. The reduction of fracture loads can occur at levels well below the yield strength of the material. Hydrogen embrittlement is usually manifest in terms of singular sharp cracks, in contrast to the extensive branching observed for stress corrosion cracking. The initial crack openings and the local deformation associated with crack propagation may be so small that they are difficult to detect except in special nondestructive examinations. Cracks due to HE can grow rapidly with little macroscopic evidence of mechanical deformation in materials that are normally quite ductile. This Technical Memorandum presents a comprehensive review of experimental data for the effects of gaseous Hydrogen Environment Embrittlement (HEE) for several types of metallic materials. Common material screening methods are used to rate the hydrogen degradation of mechanical properties that occur while the material is under an applied stress and exposed to gaseous hydrogen as compared to air or helium, under slow strain rates (SSR) testing. Due to the simplicity and accelerated nature of these tests, the results expressed in terms of HEE index are not intended to necessarily represent true hydrogen service environment for long-term exposure, but rather to provide a practical approach for material screening, which is a useful concept to qualitatively evaluate the severity of hydrogen embrittlement. The effects of hydrogen gas on mechanical properties such as tensile strength, ductility, fracture, low and high cycle fatigue, crack growth rate, and creep rupture are analyzed with respect to the general trends established from the HEE index values. It is observed that the severity of HE effects is also influenced by environmental factors such as pressure, temperature, and hydrogen gas purity. The severity of HE effects is also influenced by material factors such as surface finish, heat treatment, and product forms, compositions, grain direction, and crystal orientations.

Jonathan A. Lee↗
NASA NTRS2024

Effects of Oxide Dispersion on Failure Modes in an Additively Manufactured Superalloy

Additive manufacturing opens new paths for introducing oxide particles into superalloys, to potentially provide oxide dispersion strengthening (ODS) at high temperatures. This provides opportunities to study how such dispersions can influence failure modes for a given superalloy, after nearly identical material processing paths. The objective of this study was to compare monotonic failure modes for additively manufactured superalloys with versus without an introduced oxide dispersion. The superalloy for each case was produced by laser powder bed fusion additive manufacturing. Specimens were subsequently given consistent thermal treatment paths and then tested in tensile and creep tests at varied temperatures. Failure modes were then compared. Additively manufactured NiCrAl without ODS had randomly oriented equiaxed grains while this alloy with 0.25 wt% Y 2 O 3 ODS additions had elongated [001] oriented grains in the build direction. Material made without ODS (“No-ODS”) was nearly completely single phase gamma, while ODS additions resulted in gamma, chromium carbide, and Y-Al-Cr oxide phases, with carbide and oxide phases contents estimated at no more than 13 and 1 vol%, respectively. Compared to No-ODS, material made with ODS had higher tensile strengths at room, 760 and 1093 °C. The elongation of ODS material was lower than No-ODS at room temperature, but higher at 760 °C. At 1093 °C ODS material had higher elongation than No-ODS when tested in the build direction, however elongation was lower for ODS material in the transverse direction at 1093 °C. Creep rupture strain, life, and area reduction at 760 and 1093 °C were all much higher for ODS material compared to No-ODS; 760 °C rupture life was nearly 100 times longer for ODS material. The presence of Y in the ODS material significantly improved oxidation resistance.

supperalloys↗
DOE OSTI2022

Low-cost, high-strength, cast creep-resistant alumina-forming alloys for heat-exchangers, supercritical CO2 systems and industrial applications

An austenitic Ni-base alloy includes, in weight percent: 2.5 to 4.75 Al; 13 to 21 Cr; 20 to 40 Fe; 2 to 5 total of at least one element selected from the group consisting of Nb and Ta; 0.25 to 4.5 Ti; 0.09 to 1.5 Si; 0 to 0.5 V; 0 to 2 Mn; 0 to 3 Cu; 0 to 2 of Mo and W; 0 to 1 of Zr and Hf; 0 to 0.15 Y; 0.01 to 0.45 C; 0.005 to 0.1 B; 0 to 0.05 P; less than 0.06 N; and balance Ni (38 to 46 Ni). The weight percent Ni is greater than the weight percent Fe. An external continuous scale comprises alumina. A stable phase FCC austenitic matrix microstructure is essentially delta-ferrite-free, and contains one or more carbides and coherent precipitates of γ′ and exhibits creep rupture life of at least 100 h at 900° C. and 50 MPa.

Muralidharan, Govindarajan↗
DOE OSTI2024

Resumption of SFR Overpower Testing and Post-Transient Examination of the THOR-C-2 Irradiation Test

Transient overpower testing for fuel safety research and development has resumed at Idaho National Laboratory. The THOR-C-2 commissioning test has been performed and post-transient examination has been performed revealing the intended creep rupture failure near the top of the fuel zone. This paves the way for future testing on previously irradiated fuels that will support fuel development and qualification.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1975

Structure and elevated temperature properties of carbon-free ferritic alloys strengthened by a Laves phase

A Laves phase, Fe2Ta, was utilized to obtain good elevated temperature properties in a carbon-free iron alloy containing 1 at. pct Ta and 7 at. pct Cr. Room temperature embrittlement resulting from the precipitation of the Laves phase at grain boundaries was overcome by spheroidizing the precipitate. This was accomplished by thermally cycling the alloys through the alpha to gamma transformation. The short-time yield strength of the alloys decreased very slowly with increase in test temperature up to 600 C, but above this temperature, the strength decreased rapidly. Results of constant load creep and stress rupture tests conducted at several temperatures and stresses indicated that the rupture and creep strengths of spheroidized 1 Ta-7 Cr alloy were higher than those of several commercial steels containing chromium and/or molybdenum carbides but lower than those of steels containing substantial amounts of tungsten and vanadium. When molybdenum was added to the base Fe-Ta-Cr alloy, the rupture and creep strengths were considerably increased.

Bhandarkar, M. D.↗
NASA NTRS1995

Effects of Thermal Treatment on Tensile Creep and Stress-Rupture Behavior of Hi-Nicalon SiC Fibers

Tensile creep and stress-rupture studies were conducted on Hi-Nicalon SiC fibers at 1200 and 1400 C in argon and air. Examined were as-received fibers as well as fibers annealed from 1400 to 1800 C for 1 hour in argon before testing. The creep and rupture results for these annealed fibers were compared to those of the as-received fibers to determine the effects of annealing temperature, test temperature, and test environment. Argon anneals up to 1500 C degrade room temperature strength of Hi-Nicalon fibers, but improve fiber creep resistance in argon or air by as much as 100% with no significant degradation in rupture strength. Argon anneals above 1500 C continue to improve fiber creep resistance when tested in argon, but significantly degrade creep resistance and rupture strength when tested in air. Decrease in creep resistance in air is greater at 1200 C than at 1400 C. Mechanisms are suggested for the observed behavior.

Yun, H. M.↗
NASA NTRS1994

Tensile Creep and Stress-rupture Behavior of Polymer Derived Sic Fibers

Tensile creep and stress-rupture studies were conducted on polymer derived Nicalon, Hi-Nicalon, and SiC/BN-coated Nicalon SiC fibers. Test conditions were temperatures from 1200 to 1400 C, stresses from 100 to 1600 MPa, stress application times up to 200 hours, and air, argon, and vacuum test environments. For all fibers, creep occurred predominantly in the primary stage. Hi-Nicalon had much higher 0.2 and 1 percent creep strengths than as-produced as well as-coated Nicalon fibers. The stress-rupture strength of Hi-Nicalon up to 100 hours was also higher than that of the coated and as-produced Nicalon fibers. SiC/BN coating on Nicalon increased only the short-term low-temperature rupture strength. Limited testing in argon and vacuum suggests that for all fiber types, creep and rupture resistances are reduced in comparison to the results in air. Possible mechanisms for the observed behavior are discussed.

Yun, H. M.↗
DOE OSTI2020

A continuum damage mechanics (CDM) based Wilshire model for creep deformation, damage, and rupture prediction

In this report, a new constitutive model is derived that combines the Wilshire equations with continuum damage mechanics (CDM) to enable the long-term prediction of creep deformation, damage, and rupture. The Wilshire equations have been demonstrated to accurately extrapolate the stress-rupture, minimum-creep-strain-rate, and time-to-strain of various alloys across decade of life. Recently, the time-to-creep-strain equation has been rearranged to predict creep deformation curves; however, the resulting equation is difficult to calibrate and does not track damage. The CDM-based Sinh constitutive model accurately predicts creep deformation, damage, and stress-rupture for a variety of alloys; however, it lacks an explicit description of stress and temperature co-dependence which limits interpolation and extrapolation ability. In this study, the Wilshire and the CDM-based Sinh equations are combined to create the “WCS” model. The WCS model combines the best features of each model while eliminating their deficiencies. Experimental data for alloy P91 is gathered and the WCS model is calibrated to the data. The WCS model accurately predicts the stress rupture, minimum-creep-strain-rate, creep deformation, and damage of alloy P91 across the experimental stress and temperature range as well as consistency in parametric simulations.

36 MATERIALS SCIENCE↗