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  • 1
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    Hardening mechanisms in a dynamic strain aging alloy, Hastelloy X, during isothermal and thermomechanical cyclic deformation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The relative contributions of the hardening mechanisms in Hastelloy X during cyclic deformation were investigated by conducting isothermal cyclic deformation tests within a total strain range of +/-0.3 pct and at several temperatures and strain rates, and thermomechanical tests within several different temperature limits. The results of the TEM examinations and special constant structure tests showed that the precipitation on dislocations of Cr23C6 contributed to hardening, but only after sufficient time above 500 C. Solute drag alone produced very considerable cyclic hardening. Heat dislocation densities, peaking around 10 exp 11 per sq cm, were found to develop at temperatures producing the greatest cyclic hardening.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 23A; 551-561
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  • 2
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    Low cycle fatigue behaviour of a plasma-sprayed coating material (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Single crystal nickel-base superalloys employed in turbine blade applications are often used with a plasma spray coating for oxidation and hot corrosion resistance. These coatings may also affect fatigue life of the superalloy substrate. As part of a large program to understand the fatigue behavior of coated single crystals, fully reversed, total strain controlled fatigue tests were run on a free standing NiCoCrAlY coating alloy, PWA 276, at 0.1 Hz. Fatigue tests were conducted at 650 C, where the NiCoCrAlY alloy has modest ductility, and at 1050 C, where it is extremely ductile, showing tensile elongation in excess of 100 percent. At the lower test temperature, deformation induced disordering softened the NiCoCrAlY alloy, while at the higher test temperature cyclic hardening was observed which was linked to gradual coarsening of the two phase microstructure. Fatigue life of the NiCoCrAlY alloy was significantly longer at the higher temperature. Further, the life of the NiCoCrAlY alloy exceeds that of coated, /001/-oriented PWA 1480 single crystals at 1050 C but at 650 C the life of the coated crystal is greater than that of the NiCoCrAlY alloy on a total strain basis.
    Keywords: METALLIC MATERIALS
    Type: International Journal of Fatigue (ISSN 0142-1123); 8; 217-223
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  • 3
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    Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. III - Tension-compression anisotropy (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Single crystal superalloy specimens with various crystallographic directions along their axes were tested in compression at room temperature, 650, 760, 870, and 980 deg C. These results are compared with the tensile behavior studied previously. The alloy, Rene N4, was developed.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 17A; 507-512
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  • 4
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    Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. II - Low cycle fatigue behavior (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The low cycle fatigue (LCF) properties of a single-crystal nickel-base superalloy Rene N4, have been examined at 760 and 980 C in air. Specimens having crystallographic orientations near the 001, 011, -111, 023, -236, and -145 lines were tested in fully reversed, total-strain-controlled LCF tests at a frequency of 0.1 Hz. At 760 C, this alloy exhibited orientation dependent tension-compression anisotropies of yielding which continued to failure. Also at 760 C, orientations exhibiting predominately single slip exhibited serrated yielding for many cycles. At 980 C, orientation dependencies of yielding behavior were smaller. In spite of the tension-compression anisotropies, cyclic stress range-strain range behavior was not strongly orientation dependent for either test temperature. Fatigue life on a total strain range basis was highly orientation dependent at 760 and 980 C and was related chiefly to elastic modulus, low modulus orientations having longer lives. Stage I crack growth on 111 planes was dominant at 760 C, while Stage II crack growth occurred at 980 C. Crack initiation generally occurred at near-surface micropores, but occasionally at oxidation spikes in the 980 C tests.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 17A; 497-505
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  • 5
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    Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. I - Tensile behavior (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Single crystal specimens of a nickel-base superalloy with axes near 001, 011, and -112 were tested in tension at room temperature, 760, and 980 C. The alloy Rene N-4, was developed for gas turbine engine blades and has the nominal composition 3.7 Al, 4.2 Ti, 4 Ta, 0.5 Nb, 6 W, 1.5 Mo, 9 Cr, 7.5 Co, balance Ni, (all in weight percent). Analysis of slip band traces, specimen axis rotation, and dislocation Burgers vectors showed that at 760 and 980 C primary cube slip supplanted normal octahedral slip for the -112 line-oriented specimens. The other two orientations, which have lower resolved shear stresses on the cube system, exhibited octahedral slip at all three temperatures. The critical resolved shear stress is considerably greater on the cube system than on the octahedral system at room temperature. However, at 760 and 980 C the critical resolved shear stresses on the two systems are about the same. While the room temperature and 980 C yield strengths for the two orientations exhibiting octahedral slip could be rationalized on the basis of resolved shear stress, those at 760 C could not. Such violations of Schmid's law have previously been observed in other superalloys and single phase gamma-prime.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 17A; 491-496
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  • 6
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    Fatigue crack propagation of nickel-base superalloys at 650 deg C (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The 650 C fatigue crack propagation behavior of two nickel-base superalloys, Rene 95 and Waspaloy, is studied with particular emphasis placed on understanding the roles of creep, environment, and two key grain boundary alloying additions, boron and zirconium. Comparison of air and vacuum data shows the air environment to be detrimental over a wide range of frequencies for both alloys. More in-depth analysis on Rene 95 shows at lower frequencies, such as 0.02 Hz, failure in air occurs by intergranular, environmentally-assisted creep crack growth, while at higher frequencies, up to 5.0 Hz, environmental interaction are still evident but creep effects are minimized. The effect of B and Zr in Waspaloy is found to be important where environmental and/or creep interactions are presented. In those instances, removal of B and Zr dramatically increases crack growth and it is therefore plausible that effective dilution of these elements may explain a previously observed trend in which crack growth rates increase with decreasing grain size.
    Keywords: METALLIC MATERIALS
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  • 7
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    The characteristics of gamma-prime dislocation pairs in a nickel-base superalloy (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The gamma-prime dislocation pairs of a single crystal nickel-base superalloy, PWA 1480, after tensile and fatigue loading at 650 C are analyzed. The existence and extent of cube cross slip in octahedral slip, and the nature of gamma-prime dislocation pairs in primary cube slip are investigated. It is observed that the PWA 1480 specimens oriented near (001) and (-3 6 10) line directions deform by octahedral slip and specimens oriented near (-1 1 1) and (-2 3 4) lines deform by primary cube slip. It is determined that the overall dislocation distributions are more homogeneous in low cycle fatigue (LCF) loading than in monotonic tensile loading; however, the gamma-prime dislocation pair characteristics are similar for tensile and LCF test specimens. The data reveal that the gamma-prime dislocation pairs of octahedral slip specimens are near-screw and on the cube cross slip plane and for the cube slip specimens, the dislocation pairs are of various characters and on the primary cube slip plane.
    Keywords: METALLIC MATERIALS
    Type: Scripta Metallurgica (ISSN 0036-9748); 21; 987-992
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  • 8
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    Stress rupture and creep behavior of a low pressure plasma-sprayed NiCoCrAlY coating alloy in air and vacuum (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The creep behavior of a NiCoCrAlY coating alloy in air and vacuum at 660 and 850 C is studied. The microstructure of the coating alloy is described. Analysis of the creep curves reveal that the secondary creep rates, the transition from secondary to tertiary creep, and the strain-to-failure are affected by the environment, preexposure, stress, and temperature. It is observed that the rupture lives of the NiCoCrAlY alloy at 660 and 850 C are greater in air than in vacuum. Several mechanisms that may explain the lack of crack growth from surface-connected pores during tests in air are proposed.
    Keywords: METALLIC MATERIALS
    Type: Thin Solid Films (ISSN 0040-6090); 147; 143-152
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  • 9
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    High temperature tensile and creep behaviour of low pressure plasma-sprayed Ni-Co-Cr-Al-Y coating alloy (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The high temperature tensile and creep behavior of low pressure plasma-sprayed plates of a typical Ni-Co-Cr-Al-Y alloy has been studied. From room temperature to 800 K, the Ni-Co-Cr-Al-Y alloy studied has nearly a constant low ductility and a high strength. At higher temperatures, it becomes weak and highly ductile. At and above 1123 K, the behavior is highly dependent on strain rate and exhibits classic superplastic characteristics with a high ductility at intermediate strain rates and a strain rate sensitivity of about 0.5. At either higher or lower strain rates, the ductility decreases and the strain rate sensitivities are about 0.2. In the superplastic deformation range, the activation energy for creep is 120 + or - 20 kJ/mol, suggesting a diffusion-aided grain boundary sliding mechanism. Outside the superplastic range, the activation energy for creep is calculated to be 290 + or - 20 kJ/mol.
    Keywords: METALLIC MATERIALS
    Type: Materials Science and Engineering (ISSN 0025-5416); 83; 239-245
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  • 10
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    The tensile and fatigue deformation structures in a single crystal Ni-base superalloy (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Dislocation structures produced in Rene N4 crystals of various orientations deformed in tension and low cycle fatigue (LCF) at 760 and 980 degrees C were examined in order to elucidate the observed differences in stress-strain behavior. Specimens tensile tested at 760 degrees C displayed significant crystallographic orientation dependences in mechanical response but comparable inhomogeneous dislocation structures. LCF specimens of various orientations had comparable cyclic stress-strain curves and generally similar somewhat more homogeneous dislocation structures. Tensile specimens at the higher temperature had comparable mechanical response and corresponding similar quite homogeneous dislocation structures with gamma' faulting; and LCF specimens had orientation-dependent mechanical response but comparable homogeneous loose dislocation networks.
    Keywords: METALLIC MATERIALS
    Type: Scripta Metallurgica (ISSN 0036-9748); 20; 513-518
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