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  • Other Sources  (26)
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  • 1
    facet.materialart.
    Unknown
    Precision cast vs. wrought superalloys (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: While cast polycrystalline superalloys recommend themselves in virtue of better 'buy-to-fly' ratios and higher strengthening gamma-prime volume fractions than those of wrought superalloys, the expansion of their use into such critical superalloy applications as gas turbine hot section components has been slowed by insufficient casting process opportunities for microstructural control. Attention is presently drawn, however, to casting process developments facilitating the production of defect-tolerant superalloy castings having improved fracture reliability. Integrally bladed turbine wheel and thin-walled turbine exhaust case near-net-shape castings have been produced by these means.
    Keywords: METALLIC MATERIALS
    Type: Journal of Metals (ISSN 0148-6608); 38; 13-17
    Format: text
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  • 2
    facet.materialart.
    Unknown
    The role of cobalt on the creep of Waspaloy (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Cobalt was systematically replaced with nickel in Waspaloy (which normally contains 13% Co) to determine the effects of cobalt on the creep behavior of this alloy. Effects of cobalt were found to be minimal on tensile strengths and microstructure. The creep resistance and the stress rupture resistance determined in the range from 704 to 760 C (1300 to 1400 C) were found to decrease as cobalt was removed from the standard alloy at all stresses and temperatures. Roughly a ten-fold drop in rupture life and a corresponding increase in minimum creep rate were found under all test conditions. Both the apparent creep activation energy and the matrix contribution to creep resistance were found to increase with cobalt. These creep effects are attributed to cobalt lowering the stacking fault energy of the alloy matrix. The creep resistance loss due to the removal of cobalt is shown to be restored by slightly increasing the gamma' volume fraction. Results are compared to a previous study on Udimet 700, a higher strength, higher gamma' volume fraction alloy with similar phase chemistry, in which cobalt did not affect creep resistance. An explanation for this difference in behavior based on interparticle spacing and cross-slip is presented.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-174628 , NAS 1.26:174628
    Format: application/pdf
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  • 3
    facet.materialart.
    Unknown
    The role of the alloy matrix in the creep behavior of particle-strengthened alloys (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The strengthening microstructural features in heat-resistant super-alloys are oxide dispersoids and/or gamma-prime precipitates. The role of the strength of the alloy matrix in the creep resistance of these alloys is considered. An evaluation was made of experimental data on oxide-dispersion- and/or precipitation-strengthened nickel-based alloys with various levels of matrix solid solution strengthening; a generalized expression for creep rates which separates the matrix contributions from the particle contributions to the resisting stress and creep strength of these alloys was derived. It is concluded that the major role of the alloy matrix in the creep behavior of these alloys is in determining the apparent stress dependence of the creep rates.
    Keywords: METALLIC MATERIALS
    Type: Materials Science and Engineering; 44; July 198
    Format: text
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  • 4
    facet.materialart.
    Unknown
    Creep and stress rupture of oxide dispersion strengthened mechanically alloyed Inconel alloy MA 754 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The creep and stress rupture behavior of the mechanically alloyed oxide dispersion strengthened nickel-base alloy MA 754 was studied at 760, 982 and 1093 C. Tensile specimens with a fine, highly elongated grain structure, oriented parallel and perpendicular to the longitudinal grain direction were tested at various stresses in air under constant load. It was found that the apparent stress dependence was large, with power law exponents ranging from 19 to 33 over the temperature range studied. The creep activation energy, after correction for the temperature dependence of the elastic modulus, was close to but slightly larger than the activation energy for self diffusion. Rupture was intergranular and the rupture ductility as measured by percentage elongation was generally low, with values ranging from 0.5 to 16 pct. The creep properties are rationalized by describing the creep rates in terms of an effective stress which is the applied stress minus a resisting stress consistent with the alloy microstructure. Values of the resisting stress obtained through a curve fitting procedure are found to be close to the values of the particle by-pass stress for this oxide dispersion strengthened alloy, as calculated from the measured oxide particle distribution.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science; 11A; Sept
    Format: text
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  • 5
    facet.materialart.
    Unknown
    Effects of cobalt on structure, microchemistry and properties of a wrought nickel-base superalloy (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The effect of cobalt on the basic mechanical properties and microstructure of wrought nickel-base superalloys has been investigated experimentally by systematically replacing cobalt by nickel in Udimet 700 (17 wt% Co) commonly used in gas turbine (jet engine) applications. It is shown that the room temperature tensile yield strength and tensile strength only slightly decrease in fine-grained (disk) alloys and are basically unaffected in coarse-grained (blading) alloys as cobalt is removed. Creep and stress rupture resistances at 760 C are found to be unaffected by cobalt level in the blading alloys and decrease sharply only when the cobalt level is reduced below 8 vol% in the disk alloys. The effect of cobalt is explained in terms of gamma prime strengthening kinetics.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science; 13A; June 198
    Format: text
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  • 6
    facet.materialart.
    Unknown
    Modeling of gamma/gamma-prime phase equilibrium in the nickel-aluminum system (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A theoretical model is proposed for the determination of phase equilibrium in alloys, taking into consideration dissimilar lattice parameters. Volume-dependent pair interactions are introduced by means of phenomenological Lennard-Jones potentials and the configurational entropy of the system is treated in the tetrahedron approximation of the cluster variation method. The model is applied to the superalloy-relevant, nickel-rich, gamma/gamma-prime phase region of the Ni-Al phase diagram. The model predicts reasonable values for the lattice parameters and the enthalpy of formation as a function of composition, and the calculated phase diagram closely approximates the experimental diagram.
    Keywords: METALLIC MATERIALS
    Type: Acta Metallurgica (ISSN 0001-6160); 32; 1519-152
    Format: text
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  • 7
    facet.materialart.
    Unknown
    The elastic modulus correction term in creep activation energies Applied to oxide dispersion strengthened superalloy (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The effect of elastic modulus and the temperature dependence of elastic modulus on creep activation energies for an oxide dispersion strengthened nickel-base superalloy are investigated. This superalloy is commercially known as Inconel Alloy MA 753, strengthened both by gamma-prime precipitates and by yttria particles. It is shown that at intermediate temperatures, say below 1500 F, where elastic modulus is weakly dependent on temperature, the modulus correction term to creep activation energy is small. Accordingly, modulus corrections are insignificant for the superalloy considered, which shows high apparent creep activation energies at this temperature. On the contrary, at very high temperatures, the elastic modulus correction term can be significant, thus reducing the creep activation energy to that of vacancy self-diffusion. In order to obtain high-temperature creep resistance, a high-value elastic modulus with a weak dependence on temperature is required.
    Keywords: METALLIC MATERIALS
    Type: Scripta Metallurgica; 9; Oct. 197
    Format: text
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  • 8
    facet.materialart.
    Unknown
    Reaction kinetics between fiber and matrix (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Interdiffusion and interdiffusion controlled intermediate phase formation in metal matrix composites can be of interest for the prolonged application of these systems at high temperatures. Methods are discussed that address the kinetics of interdiffusion in systems that exhibit solid solution intermixing or the formation of a third intermediate phase at the fiber/matrix interface, or both. The tungsten fiber reinforced niobium and tungsten fiber reinforced superalloy systems are employed as model systems for experimentation and discussion. In an effort to impede interdiffusion, the concept of ion implanted diffusion barriers have been examined. Preliminary results on the feasibility and effectiveness of ion implanted diffusion barriers are presented.
    Keywords: COMPOSITE MATERIALS
    Type: Intl. Symposium on Superalloys 1988; Sept. 18-22, 1988; Champion, PA; United States
    Format: text
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  • 9
    facet.materialart.
    Unknown
    Creep and stress rupture of a mechanically alloyed oxide dispersion and precipitation strengthened nickel-base superalloy (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The creep and stress rupture behavior of a mechanically alloyed oxide dispersion strengthened (ODS) and gamma-prime precipitation strengthened nickel-base alloy (alloy MA 6000E) was studied at intermediate and elevated temperatures. At 760 C, MA 6000E exhibits the high creep strength characteristic of nickel-base superalloys and at 1093 C the creep strength is superior to other ODS nickel-base alloys. The stress dependence of the creep rate is very sharp at both test temperatures and the apparent creep activation energy measured around 760 C is high, much larger in magnitude than the self-diffusion energy. Stress rupture in this large grain size material is transgranular and crystallographic cracking is observed. The rupture ductility is dependent on creep strain rate, but usually is low. These and accompanying microstructural results are discussed with respect to other ODS alloys and superalloys and the creep behavior is rationalized by invoking a recently-developed resisting stress model of creep in materials strengthened by second phase particles.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science; 11A; Sept
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  • 10
    facet.materialart.
    Unknown
    Alloy design with oxide dispersoids and precipitates (1977)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: The mechanical behavior of particle-strengthened alloys is reviewed. On the basis of this knowledge, it is concluded that second-phase particles, coherent or incoherent, can enhance the flow strength, creep resistance, and stress-rupture life of alloys. Unfortunately, particles are usually not beneficial alloy-design elements if enhanced uniaxial ductility, plane-strain ductility, stress-rupture ductility, and toughness are called for. Such properties as fatigue-crack propagation resistance appear to require, for example, both high strength and high ductility, a situation which can come to pass only when the perennial conflict between strength and ductility is resolved in particle-strengthened systems in particular and in any other material system in general. Wherever possible, the role of coherent and incoherent particles in alloy design is distinguished.
    Keywords: METALLIC MATERIALS
    Format: text
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