The Role of Niobium in Wrought Precipitation-Hardened Nickel-Base Alloys

Smith, Gaylord D.; Patel, Saurabh K.

doi:10.7449/2005/superalloys_2005_135_154

Cited by 51 publications

(36 citation statements)

References 29 publications

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“…The substitution of Ti and Al with Nb as strengthening elements in the precipitation-hardened alloy Inconel 718 improved the resistance to postweld heat-treatment stress relaxation cracking (PWHT), because of the sluggish precipitation of the hardening phase [1,18,19]. On the other hand, many studies [6,[19][20][21] have highlighted a relationship between the presence of Nb and the formation of liquation cracking. This phenomenon is linked to the enrichment along the FZ grain boundaries in the Nb content, which is only partially solubilised in the HAZ due to the low heat input associated with LBW.…”

Section: Metallographic Analysis Inmentioning

confidence: 99%

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Lertora

Mandolfino

Gambaro

2014

International Journal of Aerospace Engineering

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Nickel alloys are very important in many aerospace applications, especially to manufacture gas turbines and aero engine components, where high strength and temperature resistance are necessary. These kinds of alloys have to be welded with high energy density processes, in order to preserve their high mechanical properties. In this work, CO2laser overlap joints between Inconel 718 sheets of limited thickness in the absence of postweld heat treatment were made. The main application of this kind of joint is the manufacturing of a helicopter engine component. In particular the aim was to obtain a specific cross section geometry, necessary to overcome the mechanical stresses found in these working conditions without failure. Static and dynamic tests were performed to assess the welds and the parent material fatigue life behaviour. Furthermore, the life trend was identified. This research pointed out that a full joint shape control is possible by choosing proper welding parameters and that the laser beam process allows the maintenance of high tensile strength and ductility of Inconel 718 but caused many liquation microcracks in the heat affected zone (HAZ). In spite of these microcracks, the fatigue behaviour of the overlap welds complies with the technical specifications required by the application.

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Section: Metallographic Analysis Inmentioning

confidence: 99%

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Lertora

Mandolfino

Gambaro

2014

International Journal of Aerospace Engineering

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“…Titanium (α + β and β) alloys are used in engine components with operating temperatures around 550 • C, which includes parts in the fan and compressor sections. Superalloys are used for components that operate above 550 • C, such as the blades, discs, vanes, and other parts found in the combustion chamber and other high-temperature engine sections [10].…”

Section: Introductionmentioning

confidence: 99%

Creep Behaviour and Microstructural Characterization of VAT 36 and VAT 32 Superalloys

Gobbi

Reis

et al. 2018

Metals

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Superalloys are used primarily for the aerospace, automotive, and petrochemical industries. These applications require materials with high creep resistance. In this work, evaluation of creep resistance and microstructural characterization were carried out at two new nickel intermediate content alloys for application in aerospace industry and in high performance valves for automotive applications (alloys VAT 32 and VAT 36). The alloys are based on a high nickel chromium austenitic matrix with dispersion of intermetallic L12 and phases containing different (Nb,Ti)C carbides. Creep tests were performed at constant load, in the temperature range of 675–750 °C and stress range of 500–600 MPa. Microstructural characterization and failure analysis of fractured surfaces of crept samples were carried out with optical and scanning electron microscopy with EDS. Phases were identified by Rietveld refinement. The results showed that the superalloy VAT 32 has higher creep resistance than the VAT 36. The superior creep resistance of the alloy VAT 32 is related to its higher fraction of carbides (Nb,Ti)C and intermetallic L12 provided by the amount of carbon, titanium, and niobium in its chemical composition and subsequent heat treatment. During creep deformation these precipitates produce anchoring effect of grain boundaries, hindering relative slide between grains and therefore inhibiting crack formation. These volume defects act also as obstacles to dislocation slip and climb, decreasing the creep rate. Failure analysis of surface fractures of crept samples showed intergranular failure mechanism at crack origin for both alloys VAT 36 and VAT 32. Intergranular fracture involves nucleation, growth, and subsequent binding of voids. The final fractured portion showed transgranular ductile failure, with dimples of different shapes, generated by the formation and coalescence of microcavities with dissimilar shape and sizes. The occurrence of a given creep mechanism depends on the test conditions. At creep tests of VAT 32 and VAT 36, for lower stresses and higher temperature, possible dislocation climb over carbides and precipitates would prevail. For higher stresses and intermediate temperatures shear mechanisms involving stacking faults presumably occur over a wide range of experimental conditions.

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“…Alloy 718 is an Ni-based, Nb-rich superalloy whose excellent mechanical properties are, in large part attributable to the precipitation of Ni 3 Nb phases: d precipitates (with a D0 a structure) and c 00 precipitates (with a D0 22 structure). Moreover, strong reactions of alloying elements with carbon to form carbides (WAC, CrAC) are used to strengthen the alloy by controlling the grain size during the elaboration process or to improve the high-temperature mechanical properties by reducing grain-boundary slippage [1][2][3].…”

Section: Introductionmentioning

confidence: 99%

DFT study of the solubility of hydrogen and carbon in Ni3Nb-D0a and
Connétable
¹
,
Galliano
²
,
Odemer
³

et al. 2014
Journal of Alloys and Compounds
21
0
0
0
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The influence of the local environment on C and H atoms was investigated in Ni 3 Nb-D0 a (space group 59) and Ni 3 Nb-D0 22 (space group 139) crystals. The interstitial positions of these atoms and their solubility energies were studied by analyzing the results of first-principles calculations based on density functional theory. The results were compared with those obtained in pure and Nb alloyed fcc Ni. For C atoms, several possible interstitial sites were found, but only one (per structure) is slightly more stable than the others: the 4d sites for D0 a and the 4c sites for D0 22. The C atom is slightly soluble and its solubility energy is equivalent in the two intermetallic structures: approximately equal to 1.06 eV, which is significantly larger than in fcc Ni (0.55 eV). In the case of hydrogen, other interstitial sites were identified: the 4e positions for both D0 a and D0 22. The solubility energy in D0 a (approximately 0.12 eV, without the zero-point energy correction) was found to be smaller than that in D0 22 (0.17 eV) but larger than that in nickel (0.09 eV). With the zero-point energy correction, the solubility in both Ni 3 Nb alloys is therefore equivalent. These results were finally used to assess the fraction of light elements in Ni 3 Nb relative to that in fcc Ni and that in Ni doped Nb.

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The Role of Niobium in Wrought Precipitation-Hardened Nickel-Base Alloys

Cited by 51 publications

References 29 publications

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Creep Behaviour and Microstructural Characterization of VAT 36 and VAT 32 Superalloys

DFT study of the solubility of hydrogen and carbon in Ni3Nb-D0a and
Connétable
¹
,
Galliano
²
,
Odemer
³

et al. 2014
Journal of Alloys and Compounds
21
0
0
0
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The Role of Niobium in Wrought Precipitation-Hardened Nickel-Base Alloys

Cited by 51 publications

References 29 publications

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

Creep Behaviour and Microstructural Characterization of VAT 36 and VAT 32 Superalloys

DFT study of the solubility of hydrogen and carbon in Ni3Nb-D0a and Connétable1, Galliano2, Odemer3 et al. 2014Journal of Alloys and Compounds21000View full textAdd to dashboardCite

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DFT study of the solubility of hydrogen and carbon in Ni3Nb-D0a and
Connétable
¹
,
Galliano
²
,
Odemer
³

et al. 2014
Journal of Alloys and Compounds
21
0
0
0
View full text Add to dashboard Cite