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Gaydosh, D. J.

Publications and source records attributed to Gaydosh, D. J..

15 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2015

On the Recovery Stress of a Ni50.3Ti29.7Hf20 High Temperature Shape Memory Alloy

Recovery stress in shape memory alloys (SMAs), also known as blocking stress, is an important property generally obtained during heating under a dimensional constraint as the material undergoes the martensitic phase transformation. This property has been instinctively utilized in most SMA shape-setting procedures, and has been used in numerous applications such as fastening and joining, rock splitting, safety release mechanisms, reinforced composites, medical devices, and many other applications. The stress generation is also relevant to actuator applications where jamming loads (e.g., in case the actuator gets stuck and is impeded from moving) need to be determined for proper hardware sizing. Recovery stresses in many SMA systems have been shown to reach stresses in the order of 800 MPa, achieved via thermo-mechanical training such as pre-straining, heat treatments or other factors. With the advent of high strength, high temperature SMAs, recovery stress data has been rarely probed, and there is no information pertinent to the magnitudes of these stresses. Thus, the purpose of this work is to investigate the recovery stress capability of a precipitation strengthened, Ni50.3Ti29.7Hf20 (at.) high temperature SMA in uniaxial tension and compression. This material has been shown to exhibit outstanding strength and stability during constant-stress, thermal cycling, but no data exists on constant-strain thermal cycling. Several training routines were implemented as part of this work including isothermal pre-straining, isobaric thermal cycling, and isothermal cyclic training routines. Regardless of the training method used, the recovery stress was characterized using constant-strain (strain-controlled condition) thermal cycling between the upper and lower cycle temperatures. Preliminary results indicate recovery stresses in excess of 1.5 GPa were obtained after a specific training routine. This stress magnitude is significantly higher than conventional NiTi stress generation capability.

Recovery Stress↗
NASA NTRS1990

Compatibility of Fe-40Al with various fibers

Chemical reaction can occur at the fiber/matrix interface of intermetallic matrix composites, leading to a degradation of mechanical properties. Fe-40Al matrix composites were fabricated using SiC, B, W, Mo-base, and Al2O3 fibers. Composite samples were heat treated up to 1500 K to study the reaction kinetics, and reaction rates were determined from reaction zone thickness measurements. The Al2O3 and W fibers were found to be compatible with the Fe-40Al matrix, while the Mo-based fibers reacted moderately and the B and SiC fibers reacted severely. Experimental results are compared to theoretical thermodynamic predictions.

Draper, S. L.↗
NASA NTRS1990

Influence of testing environment on the room temperature ductility of FeAl alloys

The effects of testing atmospheres (air, O2, N2, and vacuum) on the room-temperature ductility of Fe-40Al, Fe-40Al-0.5B, and Fe-50Al alloys were investigated. The results confirmed the decrease in room-temperature ductility of Fe-rich FeAl alloys by the interaction of the aluminide with water vapor, reported previously by Liu et al. (1989). The highest ductilities were measured in the atmosphere with the lowest moisture levels, i.e., in vacuum. It was found that significant ductility is still restricted to Fe-rich alloys (Fe-40Al), as the Fe-50Al alloy remained brittle under all testing conditions. It was also found that slow cooling after annealing was beneficial, and the effect was additive to the environmental effect. The highest ductility measurements in this study were 9 percent elongation in furnace-cooled Fe-40Al and in Fe-40Al-0.5B, when tested in vacuum.

Gaydosh, D. J.↗
NASA NTRS1990

1300 K compressive properties of several dispersion strengthened NiAl materials

To examine the potential of rapid solidification technology (RST) as a means to fabricate dispersion-strengthened aluminides, cylindrical compression samples were machined from the gauge section of their tensile specimens and tested in air at 1300 K. While microscopy indicates that RST can produce fine dispersions of TiB2, TiC and HfC in a NiAl matrix, the mechanical property data reveal that only HfC successfully strengthens the intermetallic matrix. The high stress exponents (above 10) and/or independence of strain rate on stress for NiAl-HfC materials suggest elevated temperature mechanical behavior similar to that found in oxide dispersion-strengthened alloys. Furthermore, an apparent example of departure side pinning has been observed, and as such, it is indicative of a threshold stress for creep.

Whittenberger, J. Daniel↗
NASA NTRS1989

Microstructure and tensile properties of Fe-40 at. pct Al alloys with C, Zr, Hf, and B additions

The influence of small additions of C, Zr, and Hf, alone or in combination with B, on the microstructure and tensile behavior of substoichiometric FeAl was investigated. Tensile properties were determined from 300 to 1100 K on powder which was consolidated by hot extrusion. All materials possessed some ductility at room temperature, although ternary additions generally reduced ductility compared to the binary alloy. Adding B to the C- and Zr-containing alloys changed the fracture mode from intergranular to transgranular and restored the ductility to approximately 5 percent elongation. Additions of Zr and Hf increased strength up to about 900 K. Fe6Al6Zr and Fe6Al6Hf precipitates, both with identical body-centered tetragonal structures, were identified as the principal second phase in these alloys. Strength decreased steadily as temperature increased above 700 K, as diffusion-assisted mechanisms became operative. Although all alloys had similar strengths at 1100 K, Hf additions significantly improved high-temperature ductility by suppressing cavitation.

Gaydosh, D. J.↗
NASA NTRS1989

Dispersoids in rapidly solidified B2 nickel aluminides

Rapid solidification processing has been successfully used to create a uniform distribution of 30-nm TiB2 and HfC precipitates in a B2-ordered NiAl matrix, in order to enhance the matrix material's high-temperature strength and creep behavior. Attention is drawn to the question of the stability of carbide and boride dispersoids in an NiAl matrix during high-temperature exposures. The present alloys were consolidated at temperatures above 1422 K; the small size of precipitates in materials processed at such high temperatures gives an indication of their thermal stability, and further coarsening of the precipitates at elevated service temperatures is rendered unlikely by their low solubility in the matrix.

Jha, S. C.↗
NASA NTRS1987

Dynamic recrystallization and grain boundary migration in B2 FeAl

Transmission electron microscopy and optical microscopy were used to examine polycrystalline specimens of the B2-structured alloy FeAl strained under tension to fracture at elevated temperature. Strain-induced grain boundary migration was observed above 900 K and dynamic recrystallization was found at 1000 K and 1100 K. Little evidence of dynamic recovery was evident but some networks were formed at 1100 K.

Baker, I.↗
NASA NTRS1987

The microstructure and tensile properties of extruded melt-spun ribbons of iron-rich B2 FeAl

The microstructure of extruded rods of iron-rich FeAl(B2-structure), as characterized by TEM, SEM, optical microscopy and x-ray diffractometry, consisted of elongated grains with a 111-line fibre texture containing a high dislocation density. Numerous oxide particles were found, mostly in lines which reflected the matrix flow during extrusion. In addition, some large inclusions were present. Tensile testing of annealed, relatively dislocation-free specimens as a function of increasing temperature found increasing ductility up to 900K, above which a ductility drop occurred accompanied by a change in fracture mode, from transgranular cleavage to intergranular fracture. The yield strength, which was independent of temperature up to 800K (at about 500MPa), also decreased rapidly as diffusion became more important. The predominant slip vector changed from 111-line to 100-line around 700K.

Baker, I.↗
NASA NTRS1987

Room temperature tensile ductility in powder processed B2 FeAl alloys

It has been shown that it is possible to obtain significant room temperature tensile ductility in FeAl alloys using iron-rich deviations from stoichiometry. A comparison of the room temperature tensile and compressive behaviors of Fe-50 at. pct Al and Fe-40 at. pct Al shows that FeAl is brittle at higher Al contents because it fractures along grain boundaries before general yielding. Lower aluminum contents reduce the yield stress substantially and hence some ductility is observed before fracture. Addition of boron results in measurable improvements in ductility of Fe-40 at. pct Al and is accompanied by an increase in transgranular tearing on the fracture surface, suggesting a grain boundary strengthening mechanism. Increasing the cooling rate following annealing at 1273 K results in a large increase in the yield strength and a corresponding decrease in ductility.

Crimp, M. A.↗
NASA NTRS1986

Tensile behavior of Fe-40Al alloys with B and Zr additions

Both Fe-40Al and Fe-40Al-0.1Zr with and without B were produced by the hot extrusion of powdered metal. Tensile properties were determined from room temperature to 1100 K in air. All of the materials possessed some ductility at room temperature, and addition of B caused an increase in ductility and a change in fracture mode from intergranular to transgranular cleavage. At high temperatures, failure was caused primarily by the formation of grain boundary cavities in all of the alloys. The effect of Zr addition was unclear because of the complexity of the various microstructures. Comparison of air and vacuum testing at high temperatures revealed that an apparent oxidation assisted mechanism reduced high temperature ductility in these alloys, especially at 900 K.

Gaydosh, D. J.↗
NASA NTRS1985

Ductility in rapidly solidified NiAl

An attempt is made to refine the grain structure of equiatomic NiAl by means of rapid solidification processing, and to examine the effect of small grain size on room temperature ductility. Free melt spinning was used to produce the rapidly solidified material. Room temperature bend testing of both as-spun and heat-treated NiAl ribbon was conducted by free bending the ribbon around a mandrel of successively smaller diameter until failure occurred. Room-temperature plastic deformation was exhibited both before and after a 1-h heat treatment at 1000 C. Heat treatment increased the observed ductility.

Gaydosh, D. J.↗
NASA NTRS1985

Rapidly solidified NiAl and FeAl

Melt spinning was used to produce rapidly solidified ribbons of the B2 intermetallics NiAl and FeAl. Both Fe-40Al and Fe-45Al possessed some bend ductility in the as spun condition. The bend ductility of Fe-40Al, Fe-45Al, and equiatomic NiAl increased with subsequent heat treatment. Heat treatment at approximately 0.85 T (sub m) resulted in significant grain growth in equiatomic FeAl and in all the NiAl compositions. Low bend ductility in both FeAl and NiAl generally coincided with intergranular failure, while increased bend ductility was characterized by increasing amounts of transgranular clevage fracture.

Gaydosh, D. J.↗
NASA NTRS1984

Rapidly solidified NiAl and FeAl

Melt spinning was used to produce rapidly solidified ribbons of the B2 intermetallics NiAl and FeAl. Both Fe-40Al and Fe-45Al possessed some bend ductility in the as spun condition. The bend ductility of Fe-40Al, Fe-45Al, and equiatomic NiAl increased with subsequent heat treatment. Heat treatment at approximately 0.85 T (sub m) resulted in significant grain growth in equiatomic FeAl and in all the NiAl compositions. Low bend ductility in both FeAl and NiAl generally coincided with intergranular failure, while increased bend ductility was characterized by increasing amounts of transgranular cleavage fracture.

Gaydosh, D. J.↗