Papers by J.daniel Whittenberger
Elevated-temperature deformation properties of a HfC modified Ti-48Al-2Mn-2Nb matrix particulate composite
J Mater Sci, 1994
ABSTRACT Rapid solidification techniques in combination with HIPing have been used to produce Ti-... more ABSTRACT Rapid solidification techniques in combination with HIPing have been used to produce Ti-48Al-2Mn-2Nb and a Ti-48Al-2Mn-2Nb+15 wt% HfC composite. While the composite does contain several second phases within the gamma + alpha(sub 2) matrix, none was identified to be HfC. The elevated-temperature properties were determined by constant velocity compression and constant load tensile testing in air between 1000 and 1173 K. Such testing indicated that the elevated temperature strengths of the HfC-modified aluminide was superior to those of the unreinforced matrix with the best 1100 K temperature slow strain rate properties for both materials being achieved after high-temperature annealing prior to testing. Examination of the microstructures after deformation in combination with the measured stress exponents and activation energies suggest that creep resistance of the HfC-modified form is due to solid-solution strengthening from carbon and hafnium rather than the presence of second phases.
J Mater Eng Perform, 1995
The use of the solid- to- liquid phase transformation of LiF to store thermal energy is under con... more The use of the solid- to- liquid phase transformation of LiF to store thermal energy is under consideration for a space- based solar dynamic system. Although advantageous in terms of its energy density, the melting point of this salt (1121K) is beyond the commonly accepted upper- use temperature of 1100 K for chromium- bearing superalloys in vacuum. However, one commercially available nickel- base superalloy (Hastelloy B- 2) is chromium free; unfortunately, because of its high molybdenum content, this alloy can form phases that cause high- temperature embrittlement. To test the suitability of Hastelloy B- 2, it has been exposed to molten LiF, its vapor and vacuum at 1173 K for 2500, 5000, and 10 h. For control, the chromium- containing cobalt- base Haynes alloy 188 and nickel- base Haynes alloy 230 were also exposed to LiF and vacuum at 1173 K for 5000 h. Neither LiF nor vacuum exposures had any significant effect on Hastelloy B- 2 in terms of microstructural surface damage or weight change. Measurement of the post exposure tensile properties of Hastelloy B- 2, nevertheless, revealed low tensile ductility at 1050 K. Such embrittlement and low strength at elevated temperatures appear to preclude the use of Hastelloy B- 2 as a containment material for LiF. Little evidence of significant attack by LiF was seen in either of the chromium- containing superalloys; however, considerable weight loss and near- surface microstructural damage occurred in both alloys exposed to vacuum. Although measurement of the post exposure room-temperature tensile properties of Haynes alloys 188 and 230 revealed no significant loss of strength or ductility, the severe degree of microstructural damage found in unshielded alloys exposed to vacuum indicates that chromium-bearing superalloys might also be unsuitable for prolonged containment of LiF in space above 1100 K. Keywords
Interdiffusion between the L1 2 trialuminides Al 66 Ti 25 Mn 9 and Al 67 Ti 25 Cr 8
J Mater Res, 1992
Cambridge Journals. Home; Contact Us; Site Map; Help; FAQ; Accessibility; Register. Basket; Log i... more Cambridge Journals. Home; Contact Us; Site Map; Help; FAQ; Accessibility; Register. Basket; Log in. User Log-in; Athens Log-in; Institutional Log-in. Username or Email Address: Password: Remember me. Forgot your Password? About ...
Comparative thermal fatigue resistance of several oxide dispersion strengthened alloys
Int J Fatigue, 1981
... The results for the thermal fatigue resistance of ODS alloys are in agreement with those of B... more ... The results for the thermal fatigue resistance of ODS alloys are in agreement with those of Bailey. ... MAH 'Additional thermal fatigue data on nickel-and cobalt-base superalloys; Part 2' NASA CR-121212 (1973) 5. Howes, MAH 'Thermal fatigue and oxidation data on TAZ-gA, MAR ...
Microstructure and Strengthening of Creep-Tested Cryomilled NiAl-AlN
MRS Proceedings, 1996
ABSTRACT The mechanical grinding of prealloyed NiAl powder in liquid nitrogen (cryomilling) resul... more ABSTRACT The mechanical grinding of prealloyed NiAl powder in liquid nitrogen (cryomilling) results in an intermetallic matrix composite where micron sized particle free aluminide cores (grains) are surrounded by thin mantles comprised of nanometer sized A1N particles and NiAl grains. Under high temperature, slow strain rate conditions both compressive and tensile creep testing have shown that the mechanical strength of hot extruded cryomilled NiAl approaches the levels exhibited by advanced NiAl-based single crystals and simple Ni-based superalloys. Transmission electron microscopy of cryomilled materials tested between 1100 and 1300 K revealed little, if any, dislocation structure within the mantle regions, while the NiAl cores contained subgrains and dislocation networks after testing at all strain rates between 10-4 and 10-8 s-1. These and other microstructural observations suggest that creep strength is the result of a fine NiAl grain/subgrain size, the inability of dislocations to move through the mantle and stabilization of the microstracture by the A1N particles.
Elevated Temperature Flow Strength, Creep Resistance and Diffusion Welding Characteristics of Ti-6 AI-2 Nb-1Ta-0.8 Mo
Metall Mater Trans a, 1979
ABSTRACT A study of the flow strength, creep resistance and diffusion welding characteristics of ... more ABSTRACT A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been essentially processed above the beta transus (∼1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A “soft” interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.
1300 K Compressive Properties of Directionally Solidified Ni-33Al-33Cr-1Mo
MRS Proceedings, 2000
Intermetallics, 1995
ELSEVIER 0966-9795(95)00008-9 lntermetallics 3 (1995) 493 503 _,1995 Elsevier Science Limited Pri... more ELSEVIER 0966-9795(95)00008-9 lntermetallics 3 (1995) 493 503 _,1995 Elsevier Science Limited Printed in Great Britain. All rights reserved 0966-9795/95/$09,50
Fluoride salts and container materials for thermal energy storage applications in the temperature range 973 - 1400 K
Iecec 87 Proceedings of the Twenty Second Intersociety Energy Conversion Engineering Conference, 1987
Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat st... more Multicomponent fluoride salt mixtures were characterized for use as latent heat of fusion heat storage materials in advanced solar dynamic space power systems with operating temperatures in the range of 973 to 1400 K. The melting points and eutectic composition for many systems with published phase diagrams were verified, and several new eutectic compositions were identified. Additionally, the heats of fusion of several binary and ternary eutectics and congruently melting intermediate compounds were measured by differential scanning calorimetry. The extent of corrosion of various metals by fluoride melts was estimated from thermodynamic considerations, and equilibrium conditions inside a containment vessel were calculated as functions of the initial moisture content of the salt and free volume above the molten salt. Preliminary experimental data on the corrosion of commercial, high-temperature alloys in LiF-19.5CaF2 and NaF-27CaF2-36MgF2 melts are presented and compared to the thermodynamic predictions.
Use of pure nickel and LiOH for thermal energy storage
Journal of Materials Engineering, 1988
ABSTRACT The solid to liquid phase transformation of LiOH has been proposed as an ideal candidate... more ABSTRACT The solid to liquid phase transformation of LiOH has been proposed as an ideal candidate thermal energy storage media for a Rankine Cycle powered electrical generation unit envisioned in Space Station based solar dynamic systems. Due to the corrosive nature of molten hydroxides, long term containment of LiOH is of concern. Pure nickel is thought to be a suitably resistant material, and a program has been instituted to measure the effects of prolonged exposure of liquid and gaseous LiOH on the mechanical properties of pure nickel alloys. Results to date indicate that negligible weight and thickness changes occurred in Ni alloys exposed to LiOH for as long as 2500 hr at 775 K, and essentially no difference in 77-900 K tensile properties could be detected between LiOH exposed and vacuum annealed Ni specimens. Although there was little sign of outward damage, microstructural examination revealed that all hydroxide contaminated tensile test specimens had surface connected intergranular cracks along the gage lengths. Two other potential problems, which have strong implications with respect to a LiOH/Ni energy storage system, were also noted during the corrosion experiments. In particular stress corrosion cracking of weld joints in pressurized vessel and permeation of hydrogen through nickel were observed.
Metall Mater Trans a, 1977
The room temperature and 1365 K tensile properties and 1365 K tensile creep properties at low str... more The room temperature and 1365 K tensile properties and 1365 K tensile creep properties at low strain rates were measured for several oxide dispersion strengthened (ODS) alloys. The alloys examined included ODS Ni, ODS Ni-20Cr and ODS Ni-16Cr-4J5Al. Metallography of creep tested, large grain size ODS alloys indicated that creep of these alloys is an inhomogeneous process. All alloys appear to possess a threshold stress for creep. It is believed that the threshold stress is associated with diffusional creep in the large grain size ODS alloys and normal dislocation motion in perfect single crystalline ODS alloys. Threshold stresses for large grain size ODS Ni-20Cr and Ni-16Cr-4J5A1 type alloys are dependent on the grain aspect ratio. Because of the deleterious effect of prior creep on room temperature mechanical properties of large grain size ODS alloys, it is speculated that the threshold stress may be the design-limiting creep strength property.
High-temperature slow-strain-rate compression studies on CoAI-TiB 2 composites
Metall Mater Trans a, 1990
ABSTRACT Results are presented of compressive deformation tests performed on particulate-reinforc... more ABSTRACT Results are presented of compressive deformation tests performed on particulate-reinforced CoAl-TiB2 composites in the temperature range 1100-1300 K. Hot-pressed and postdeformation microstructures were characterized by TEM and by optical microscopy. It was found that the addition of TiB2 particles improves the deformation resistance of the matrix, due to dislocation-particle interactions.
A Review of: "SUPERALLOYS II" edited by CT. Sims, N.S. Stoloff, and W.C. Hagel A Wiley-Interscience Publication John Wiley & Sons, New York, NY 615 pages, hardcover, 1987
Mater Manuf Process, 1992
J Mater Sci, 1988
The compressive slow plastic flow behaviour of several B2 crystal structure NiAI intermetallics h... more The compressive slow plastic flow behaviour of several B2 crystal structure NiAI intermetallics has been studied in air between 1000 and 1400 K (-,~0.53 to 0.74 T M). Small grain-sized Ni-48.25at%AI (~5 and 10#m) was found to be stronger than the previously studied 17/~m diameter material. While grain refinement improved the strength at all test temperatures, the exact mechanism is not clear. Experiments at lower temperature revealed that composition as well as grain size can be an important factor, since Ni-49.2AI was weaker than Ni-48.25AI. Pronounced yield points were found during slow strain-rate testing at 1000 K; however, continued deformation appears to take place by the same mechanism(s) as found at high temperatures. Small changes in thermomechanical processing (TMP) schedules to fabricate Ni-49.2AI indicated that basic deformation characteristics (stress exponent and activation energy) are not affected; however, the pre-exponential term could be modified if TMP alters the grain structure.
Preliminary investigation of inertia friction welding B2 aluminides
Journal of Materials Science Letters, 1987
ABSTRACT An attempt is made to achieve inertia friction-welding in FeAl and NiAl samples, taking ... more ABSTRACT An attempt is made to achieve inertia friction-welding in FeAl and NiAl samples, taking into account their intermetallics' compositions, extrusion parameters, and microstructural data. The energy required for the weld is stored in a rotating flywheel mass attached to one of the two pieces to be joined; when enough energy is introduced, the flywheel is disconnected and an axial load is applied which forces the spinning piece against the stationary one, converting the energy into heat by means of friction. Due to the inherent brittleness of the aluminides, a step-load program was used in which an initial, low-pressure heat buildup increased the work pieces' ductility.
Compression behavior of the forged L12 compounds Al67Ti25Cr8 and Al66Ti25Mn9
Scripta Metallurgica Et Materialia, 1990
ABSTRACT The paper presents the findings of a compression study as a function of temperature from... more ABSTRACT The paper presents the findings of a compression study as a function of temperature from cryogenic temperatures to 1373 K at a strain rate of about 0.0001/s on forged Al67Ti25Cr8 and Al66Ti25Mn9 compounds. The creep response of these alloys is analyzed at strain rates varying from 2 x 10 to the -4th to 2 x 10 to the -7th /s at 1000 K and 1100 K. It is shown that as-cast microstructures for both compounds are dendritic, while both intermetallics forged very well with no edge cracking, with the microstructures appearing fully recrystallized. True comprehensive stress-strain diagrams determined at 1100 K as a function of nominal strain rate reveal a range of behaviors in both materials.
J Mater Eng Perform, 1994
As a continuation of a study of a space-based thermal energy storage system centered on a LiF-CaF... more As a continuation of a study of a space-based thermal energy storage system centered on a LiF-CaF2 eutectic salt contained by Haynes alloy 188, this Co-base superalloy was subjected to molten salt, its vapor, and vacuum for 22,500 h at 1093 K. Samples from all three exposure conditions were tensile tested between 77 to 1200 K; in addition, vacuum and molten-salt exposed specimens were vacuum creep rupture tested at 1050 K. Comparison of these mechanical properties with those measured for the as-received alloy reveals no evidence for degradation beyond that ascribed to simple thermal aging of Haynes alloy 188. This behavior is identical to the 10,000 h results (Ref 3); hence, Haynes alloy 188 is a suitable containment material for an eutectic LiF-CaF2 thermal energy storage salt.
Effect of Strain Rate on the Fracture Behavior at 1366 K of the bcc Iron Base Oxide Dispersion Strengthened Alloy MA 956
Metall Mater Trans a, 1979
The tensile behavior of the oxide dispersion strengthened iron-base alloy MA 956 was investigated... more The tensile behavior of the oxide dispersion strengthened iron-base alloy MA 956 was investigated as a function of strain-rate ranging from 3.3×10-2 to 8.3×10-8 s-1 at 1366 K. All tests were conducted in the longitudinal direction on specimens machined from bar stock. Because of the microstructure of this alloy, all specimens were either single crystals or bicrystals with the boundary parallel to the gage length. Testing revealed that the strength was rather insensitive to strain-rate, the tensile ductility decreased with decreasing strain-rate, and for strain-rates ≤8.3×10-5 s-1, the alloy fractured in brittle manner. Evidence of transgranular cracking perpendicular to the applied stress was observed at all strain-rates; failure at strain-rates ≤8.3×10-5 s-1 was due to cracks which grow by the joining together of cavities ahead of the running crack. This alloy appears to possess a critical stress intensity factor for rapid crack growth.
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Papers by J.daniel Whittenberger