On precipitate shearing by superlattice stacking faults in superalloys

Caron, Pierre; Khan, T.; Veyssière, P.

doi:10.1080/01418618808204522

Cited by 120 publications

(22 citation statements)

References 12 publications

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“…Close inspection decomposed at the interface recombined on exiting the ␥ Ј particle and left behind a faulted loop as debris. [9][10][11][12]14] If of Figure 13 reveals several features which clarify the analysis. First, there were a number of dislocation pairs in the the faults are confined to the ␥ Ј particles, as in the case of the subsolvus alloy and the 0.2 to 0.35 m unimodal alloys, matrix, some of which are marked in Figure 13(c).…”

Section: Analysis Of the Stacking Faultsmentioning

confidence: 93%

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

Sinharoy

Virro-Nic

Milligan

2001

Metall Mater Trans A

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Two powder metallurgy nickel-base turbine disk alloys, RENE'95* and KM4, were studied for *RENE'95 is a trademark of General Electric Company, Fairfield, CT. strength and deformation behavior at 650 ЊC. Two classes of microstructures were investigated: unimodal size distributions of ␥ Ј precipitates with particle sizes ranging from 0.1 to 0.7 m and commercially heat-treated structures with bimodal or trimodal size distributions of ␥ Ј precipitates. The strength and deformation mechanisms were heavily influenced by the microstructure. In both alloys, deformation during compression tests consisted of a combination of a/2͗110͘ antiphase boundary (APB)-connected dislocation pairs and a/3͗112͘ partials creating superlattice intrinsic stacking faults (SISFs). In unimodal alloys, the fault density increased with decreasing particle size and decreasing strain rate. These trends, observed in compression testing, are consistent with earlier studies of similar alloys, which were tested in creep. As the ␥ Ј size was reduced, the nature of the faults changed from being isolated within single precipitates to being extended across entire grains. Commercially heat-treated alloys, containing a bimodal distribution of ␥ Ј particles, exhibited significantly more faulting than unimodal alloys at the same cooling ␥ Ј size. This augmentation of the faulting in commercial alloys was apparently due to the presence of the fine, aging ␥ Ј particles. The two typical commercial heat treatments (supersolvus and subsolvus) resulted in different deformation structures: the subsolvus behavior was similar to that of unimodal alloys with ␥ Ј sizes between 0.2 and 0.35 m, while the supersolvus deformation was similar to that of unimodal alloys with the 0.1 m ␥ Ј size. These differences were attributed to differences in the size of the fine, aging ␥ Ј particles. Creep deformation in a commercially heat-treated material at 650 ЊC occurred solely by SISF-related mechanisms, resulting in a macroscopic slip vector of ͗112͘. The effects of alloy chemistry, APB energy, and microstructure on the deformation and mechanical behavior are discussed in detail, and possible effects of the faulting mechanisms on the mechanical behavior are explored. Finally, models for yield strength as a function of microstructure for bimodal alloys with large volume fractions of precipitates are found to be in need of development.

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Section: Analysis Of the Stacking Faultsmentioning

confidence: 93%

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

Sinharoy

Virro-Nic

Milligan

2001

Metall Mater Trans A

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“…In Ni-based superalloys where γ′ is the prime-strengthening phase, a rich variety of deformation modes have been reported [11][12][13][14][15][16][17][18]. The precipitates themselves are unique in that during deformation, the γ′ precipitates impart resistance to plastic deformation since they act as effective γ γ γ γ 7th International Symposium on Superalloy 718 and Derivatives Edited by:…”

Section: Introductionmentioning

confidence: 99%

“…This combination of changes enables the precipitation of ordered L1 2 structured (Ni 3 Al,Ti) based γ′ precipitates that are coherently embedded in a solid solution γ matrix [9][10]. It is expected that the alteration of the prime-strengthening constituent from γ′′ to γ′ will have a significant effect on the thermal stability of this alloy as well as the high temperature mechanical properties.In Ni-based superalloys where γ′ is the prime-strengthening phase, a rich variety of deformation modes have been reported [11][12][13][14][15][16][17][18]. The precipitates themselves are unique in that during deformation, the γ′ precipitates impart resistance to plastic deformation since they act as effective γ γ γ γ 7th International Symposium on Superalloy 718 and Derivatives Edited by:…”

mentioning

confidence: 99%

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus®

Unocic¹,

Daehn²,

Unocic³

et al. 2010

7th International Symposium on Superalloy 718 and Derivatives (2010)

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A preliminary study on the evolution of creep deformation substructure in Ni-base superalloy Allvac 718Plus has been performed. Specimens crept at 620 MPa and at temperatures ranging from 690-732ºC were examined utilizing diffraction contrast TEM characterization techniques.Creep was interrupted at 1-2.5% strain in order to study the deformation substructure following a limited amount of deformation. The dominant deformation modes at each of the test temperatures were highly planar in nature and involved shearing of the matrix and ′ precipitates on {111} glide planes. In addition, paired a/2<110> dislocations were evident which suggest an antiphase boundary shearing mechanism. Creep induced microtwinning was also observed at the highest creep temperature which was created by identical a/6<112> Shockley partial dislocations that shear the matrix and ′ precipitates on consecutive close packed {111} glide planes. IntroductionNi-based superalloys are predominately utilized in aircraft and land-based industrial gas turbine engines where they excel in the retention of mechanical properties during service at elevated temperatures. In order to improve both engine performance and efficiency significant emphasis has been placed on developing alloys that can operate at higher temperatures without significant loss in structural integrity. In the conventional 718 alloy, the upper bound service temperature is limited to ∼650º, which is governed primarily by microstructural instability through coarsening of the prime strengthening DO 22 structured Ni 3 Nb-based γ′′ precipitate phase followed by its transformation to the equilibrium orthorhombic Ni 3 Nb δ-phase [1][2][3][4][5][6]. With this in mind, Allvac 718Plus was developed with the specific goal of increasing the temperature capability by ∼55ºC while maintaining the excellent workability and weldability characteristics of 718 [7][8]. The alloy chemistry was modified such that the Fe content was reduced while the W, Co and Al/Ti ratio was increased. This combination of changes enables the precipitation of ordered L1 2 structured (Ni 3 Al,Ti) based γ′ precipitates that are coherently embedded in a solid solution γ matrix [9][10]. It is expected that the alteration of the prime-strengthening constituent from γ′′ to γ′ will have a significant effect on the thermal stability of this alloy as well as the high temperature mechanical properties.In Ni-based superalloys where γ′ is the prime-strengthening phase, a rich variety of deformation modes have been reported [11][12][13][14][15][16][17][18]. The precipitates themselves are unique in that during deformation, the γ′ precipitates impart resistance to plastic deformation since they act as effective γ γ γ γ 7th International Symposium on Superalloy 718 and Derivatives Edited by:

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“…One reason for the higher CRSS of the γ' phase is the difficulty of entry of dislocations from the γ phase into the γ' phase. In [30], shearing of γ' has been observed through pairs of a/2<110> dislocations in the γ phase, which then propagate as a super dislocation in the γ' phase. The associated RSS can be estimated using the formula:…”

Section: Tension Test Of Ds Alloy At 900 Cmentioning

confidence: 99%

Elastic Microstrains during Tension and Creep of Superalloys: Results from In Situ Neutron Diffraction

Lu¹,

Ma²,

Majumdar³

2008

Superalloys 2008 (Eleventh International Symposium)

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In situ neutron diffraction experiments were conducted to monitor elastic microstrains during tension and creep of a directionally solidified (DS) superalloy PWA1422 and a single crystal (SX) alloy PWA 1484. The rationale was to obtain insight on internal stress evolution, and thereby improved understanding of deformation mechanisms. The misfit between the gamma (γ) and gamma-prime (γ') phases were determined as a function of temperature and deformation. The microstrains in the tension test were used to obtain the critical resolved shear stress (CRSS) of the phases. Results show a dramatic increase in the CRSS of the γ-phase compared to the bulk, and are consistent with dislocations bowing (Orowan type) between narrow γ-channels. A threshold stress is calculated for dislocation activity in the horizontal channel, and is suggested as a minimum stress for initiating any creep or rafting. Microstrains from the creep test at 900°C/425 MPa are consistent with the formation of dislocation networks, but the data do not suggest that the CRSS is exceeded for cutting of the γ'. Rather, rafting is suggested for the onset of tertiary creep. At 1092°C/120 MPa, the far-field creep strain exhibits an unusual behavior in the pre-steady-state low strain (<0.5%) regime. This is also accompanied with creep acceleration and decrease of elastic strain in γ'. The response is accompanied with the formation of a completely rafted microstructure. An explanation is provided in terms of deposition of actual misfit dislocations preferentially on the vertical interfaces.

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On precipitate shearing by superlattice stacking faults in superalloys

Cited by 120 publications

References 12 publications

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus®

Elastic Microstrains during Tension and Creep of Superalloys: Results from In Situ Neutron Diffraction

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On precipitate shearing by superlattice stacking faults in superalloys

Cited by 120 publications

References 12 publications

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

Deformation and strength behavior of two nickel-base turbine disk alloys at 650 °C

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus&reg;

Elastic Microstrains during Tension and Creep of Superalloys: Results from In Situ Neutron Diffraction

Contact Info

Product

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A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus®