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  • 1
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    Hydrogen effects in 001-line oriented nickel-base superalloy single crystals (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The entry and subsequent interaction of hydrogen on the mechanical properties of the single crystal nickel-base superalloy CMSX-2 has been studied. Significant amounts of hydrogen were introduced by high temperature hydrogen charging in molten salts which led to an increased lattice parameter and microhardness and to a degradation in tensile elongation to failure whose extent scales with the depth of the hydrogenated zone. In this region a fracture mode change from a 111 to a 100 plane type also occurred. The values of the binding energy of hydrogen to solidification voids and the effective hydrogen pressure in the voids were estimated.
    Keywords: METALLIC MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 19A; 73-82
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  • 2
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    Dynamic recrystallization and grain boundary migration in B2 FeAl (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: 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.
    Keywords: METALLIC MATERIALS
    Type: Metallography (ISSN 0026-0800); 20; 347-357
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  • 3
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    Role of Hydrogen and Structure on CMSX-2 (1985)
    In:  CASI
    Details
    Publication Date: 2014-09-04
    Description: The goal was to characterize and understand the detailed effect of hydrogen on the tensile and fatigue behavior of single crystals of CMSX-2. Specimens were solutionized, air cooled, and then aged in one of two ways. The resultant macro and microstructure included a pronounced dendritic structure with numerous low angle boundaries in the interdendritic region and on the average a high level of porosity with a large variation in size and distribution. Hydrogen permeability and diffusivity in this material was found to be very low at room temperature. Hydrogen concentration studies on thin samples yielded values significantly higher than found for similar charging conditions in nickel and stainless steels. The tensile mechanical properties were found to depend on hydrogen concentration. SEM observations of the brittle subsurface zone revealed a strong correlation between crack initiation sites and voids just beneath the surface. The hollow and solid samples were compared to better understand the influence of increased charged volume on the fatigue behavior.
    Keywords: METALLIC MATERIALS
    Type: NASA. Lewis Research Center Struct. Integrity and Durability of Reusable Space Propulsion Systems; p 171-180
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  • 4
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    Characterization of hydrogen embrittlement in nickel base superalloy single crystals (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In order to study the role of CMSX2 single crystal microstructure on the combined stress-hydrogen environment effects, hydrogen was introduced by cathodic charging. Concentration measurements were carried out to investigate the dependence of hydrogen solubility and trapping on microstructure. Mechanical properties were measured at room temperature on smooth tensile specimens as a function of heat treatment, crystal orientation and H charging conditions. SEM and TEM allow to study H induced cracks initiation and propagation. A large amount of hydrogen can be dissolved and trapped in CMSX2 single crystals when exposed to a high hydrogen fugacity environment. The strong H trapping evidenced in voids explains the predominant role of these defects as crack initiation sites. The strong detrimental effect of hydrogen on the material tenacity is discussed.
    Keywords: METALLIC MATERIALS
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  • 5
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    Room temperature tensile ductility in polycrystalline B2 Ni-30Al-20Fe (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A room-temperature tensile elongation of about 2.5 percent, where the only slip vector observed was the 100, has been determined for a double-extruded B2 Ni-30Al-20Fe alloy consisting of recrystallized equiaxed grains about 25 microns in diameter; these results suggest that 100-slip does not preclude limited ductility in polycrystalline B2 alloys in tension at low temperatures. A suppression of ordering through resort to rapid solidification, in other words, is not necessary for ductility, since the cast and as-extruded alloy presently examined is ordered.
    Keywords: METALLIC MATERIALS
    Type: Scripta Metallurgica (ISSN 0036-9748); 23; 897-900
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  • 6
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    The microstructure and tensile properties of extruded melt-spun ribbons of iron-rich B2 FeAl (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: 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.
    Keywords: METALLIC MATERIALS
    Type: High-temperature ordered intermetallic alloys II; Dec 02, 1986 - Dec 04, 1986; Boston, MA; United States
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  • 7
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    Improving the low temperature ductility of NiAl (1989)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: As part of a study aimed at developing a ductile NiAl-based alloy, ingots of Ni-Fe-Al alloys were cast and hot extruded to rods. The purpose of the iron additions was two-fold viz; to produce a change in the slip vector from 001 to 111 line and, in one alloy, to add a L1(2)-structured ductile second phase. Extruded Ni-20Al-30Fe was two-phase, containing a pro-eutectic B2 phase in a fine lamellar structure of B2+L1(2) phases. Room temperature tensile testing of both single extruded and double extruded alloys resulted in 8-percent and 22-percent plastic elongation and yield stresses of 850 and 760 MPa, respectively. Fracture in both cases occurred by ductile tearing of the eutectic and transgranular cleavage of the proeutectic phase at 1350 MPa. The ductility in double extruded condition is higher than that reported earlier in rapidly solidified wires by Inoue et al. (1984). By comparison, extruded single-phase B2-structured Ni-30Al-20Fe exhibited a fracture strength of 780 MPa, no plasticity, and a mixture of intergranular fracture and transgranular cleavage. This is contrast to earlier work by Inoue et al. where a yield stress of 400 MPa, 5 percent plastic strain, and a mixture of dimple and intergranular fracture was reported.
    Keywords: METALLIC MATERIALS
    Type: Symposium on High-Temperature Ordered Intermetallic Alloys III; Nov 29, 1988 - Dec 01, 1988; Boston, MA; United States
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