High Temperature Degradation of Alloy 718 after Longtime Exposures

Radavich, J.F.; Korth, G.E.

doi:10.7449/1992/superalloys_1992_497_505

Cited by 18 publications

(11 citation statements)

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“…The structural results of our own study are essentially in agreement with the Table II summary and our microscopic examination verities the SEM microstructures published by Radavich and Korth (16). The use of the cryogenic, metholic-perchloric electrolytes, allows the preparation of structures containing high chromium precipitates without their loss , as occurs when the SEM specimen is prepared at ambient temperatures or in other electrolytes such as metholic-hydrochloric.…”

Section: Discussionsupporting

confidence: 90%

The Effects of Long Time Exposure on Alloy 718

Wlodek¹,

Field²

1994

Superalloys 718, 625, 706 and Various Derivatives (1994)

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Measurements of gamma prime (y') and gamma double prime (y") size were made on Inconel alloy 718 exposed for up to 50,000 hr's, in the temperature range of 538 to 704 "C (1000 to 1300 "F ). All materials were from either the original Barker, Ross and Radavich study, where the specimens were exposed under stress, or the more recent Korth work that utilized unstressed exposures. The diameter of the y' and y" phases, D' and D" ( in pm ), were measured and could be correlated through a Larsen -Miller parameter ( P = T [ 25+ log t 1 ) to the temperature ( T in OK ) and the time of exposure ( t in hr's ) . The following relationships were established : These relationships were derived using materials of varying chemistry, processing and heat treatment, exposed with and without stress. In addition, where suitable mechanical data were available, it was possible to establish regression equations between the y " diameter and simple mechanical properties. High resolution scanning electron microscopy, that allows accurate precipitate measurement, can thus be used to estimate service temperature and approximate residual properties in parts after prolonged service. This technique is effective regardless of the stress level, or slight, in specification, variations in chemistry, processing or heat treatment.Detailed AEM studies were performed on material exposed 50,000 hr's. at 649 C ( 1200 OF ). These lead to the definite identification of c(-Cr, a high Cr and MO Iaves phase, and small amounts of a sigma phase, as forming during prolonged exposure, in addition to the standard y ' , y I', delta, and MC phases. More extensive SEM studies, backed up by energy dispersive x -ray analysis, were utilized to follow these precipitation reactions over the whole range of time and temperature studied here. It was possible to conclude that the precipitation of a-Cr and the other minor phases in alloy 718 are driven by the almost complete rejection of Cr and MO that results in advance of the growing delta phases.

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Section: Discussionsupporting

confidence: 90%

The Effects of Long Time Exposure on Alloy 718

Wlodek¹,

Field²

1994

Superalloys 718, 625, 706 and Various Derivatives (1994)

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“…It appears that the microstructures developed in longtime exposures of alloy 625 at 1200'F are similar to some of those found in alloy 718 in longtime exposures at 1300'F and 1400°F, namely Ni3 Cb, 1/', and aCr [4]. Unlike alloy 718, alloy 625 does not form sigma or f because of the low Fe and Al + Ti contents but forms MgC due to its high MO content.…”

Section: Discussionmentioning

confidence: 57%

Effects of Long-Time Exposure in Alloy 625 at 12OO�F, 1400�F and 1600�F

Radavich¹,

Fort²

1994

Superalloys 718, 625, 706 and Various Derivatives (1994)

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“…It is commonly accepted that the mechanical properties dropping in Inconel 718 after long-time thermal exposure at high temperature is caused by the coarsening of γ″ (Ni 3 Nb) and γ′ (Ni 3 (Ti, Al)), as well as the transformation of γ″ to a more stable δ (Ni 3 Nb) phase. Besides, the precipitation of body-centered cubic α-Cr phase can be another possible factor that affects the mechanical properties [7][8][9][10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Mechanism of α-Cr precipitation and crystallographic relationships between α-Cr and δ phases in Inconel 718 alloy after long-time thermal exposure

Dong

Zhang

et al. 2010

Int J Miner Metall Mater

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To study the precipitation mechanism of α-Cr phase in Inconel 718 alloy, the samples after long-time aging at 650 and 677°C were examined by microstructural observations and chemical phase analysis methods. Combining the thermodynamics and kinetics calculation results, α-Cr always precipitates in the vicinity of δ phase, because δ phase rejects Cr into the γ-matrix when growing. The selected area diffraction patterns confirm that the crystallographic relationships of α-Cr with δ phase are (010) δ //( 1 10) α-Cr and [100] δ //[111] α-Cr . A graphic model is also presented to show the crystallographic relation between α-Cr and δ phases.

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High Temperature Degradation of Alloy 718 after Longtime Exposures

Cited by 18 publications

References 0 publications

The Effects of Long Time Exposure on Alloy 718

The Effects of Long Time Exposure on Alloy 718

Effects of Long-Time Exposure in Alloy 625 at 12OO�F, 1400�F and 1600�F

Mechanism of α-Cr precipitation and crystallographic relationships between α-Cr and δ phases in Inconel 718 alloy after long-time thermal exposure

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