Diffusion processes during creep at intermediate temperatures in a Ni-based superalloy

Smith, Timothy M.; Rao, You; Wang, Y.; Ghazisaeidi, Maryam; Mills, Michael J.

doi:10.1016/j.actamat.2017.09.027

Cited by 97 publications

(35 citation statements)

References 29 publications

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“…[29] Therefore, in the light of this, it seems reasonable to assume that as a first approximation, the lengthening of the different faults under these conditions (800°C and 650 MPa) is governed by the segregation of c-stabilizers to the fault. This is further supported by the work of Smith et al [30] where a comparative study of the lengthening rates for the different diffusion processes taking place is presented. This picture of the plastic deformation proposed here is probably applicable across a range of medium-high temperatures and high stresses.…”

Section: A Segregation-assisted Shearingsupporting

confidence: 60%

Segregation-Assisted Plasticity in Ni-Based Superalloys

Barba

Smith

Miao

et al. 2018

Metall Mater Trans A

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Correlative high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy are used to study deformation-induced planar faults in the single-crystal superalloy MD2 crept at 800°C and 650 MPa. Segregation of Cr and Co at microtwins, anti-phase boundaries (APB), and complex/superlattice extrinsic and intrinsic stacking faults (CESF/SESF and CISF/SISF) is confirmed and quantified. The extent of this is found to depend upon the fault type, being most pronounced for the APB. The CESF/SESF is studied in detail due to its role as a precursor of the microtwins causing the majority of plasticity under these conditions. Quantitative modeling is carried out to rationalize the findings; the experimental results are consistent with a greater predicted velocity for the lengthening of the CESF/ SESF-compared with the other types of fault-and hence confirm its role in the diffusion-assisted plasticity needed for the microtwinning mechanism to be operative.

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Section: A Segregation-assisted Shearingsupporting

confidence: 60%

Segregation-Assisted Plasticity in Ni-Based Superalloys

Barba

Smith

Miao

et al. 2018

Metall Mater Trans A

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“…Maintaining the microstructural integrity of these materials during operation is a paramount challenge in this field [1,2]. Most investigations of the microstructural changes during high temperature deformation focus on the main precipitation strengthening phase in the superalloys, the γ' precipitates, and its evolution over time in terms of size [3,4], volume fraction [5,6], shape [7,8], composition [9][10][11] and its different deformation mechanisms occurring under various thermal loading scenarios [12][13][14][15][16]. However, little attention has been paid so far to the minor elements, such as carbon and boron and their associated phases, which can also have major consequences for the mechanical performance of superalloys.…”

Section: Introductionmentioning

confidence: 99%

Influence of composition and precipitation evolution on damage at grain boundaries in a crept polycrystalline Ni-based superalloy

et al. 2019

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The microstructural and compositional evolution of intergranular carbides and borides prior to and after creep deformation at 850 °C in a polycrystalline nickel-based superalloy was studied. Primary MC carbides, enveloped within intergranular γ' layers, decomposed resulting in the formation of layers of the undesirable  phase. These layers have a composition corresponding to Ni3Ta as measured by atom probe tomography and their structure is consistent with the D024 hexagonal structure as revealed by transmission electron microscopy. Electron backscattered diffraction reveals that they assume various misorientations with regard to the adjacent grains. As a consequence, these layers act as brittle recrystallized zones and crack initiation sites. The composition of the MC carbides after creep was altered substantially, with the Ta content decreasing and the Hf and Zr contents increasing, suggesting a beneficial effect of Hf and Zr additions on the stability of MC carbides. By contrast, M5B3 borides were found to be microstructurally stable after creep and without substantial compositional changes. Borides at 850 °C were found to coarsen, resulting in some cases into γ'depleted zones, where, however, no cracks were observed. The major consequences of secondary phases on the microstructural stability of superalloys during the design of new polycrystalline superalloys are discussed.

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“…[40] Recent studies have identified diffusion-activated plasticity as an additional operating mechanism which could explain the decreasing strength in this temperature regime. [41,42] A further significant weakening effect at higher temperatures is a decrease in c 0 volume fraction, / p . Calculations using Thermo-Calc and the TTNi8 Ni-alloy database predict a decrease from 58 pct at 600°C to nearly 0 pct at 1150°C (see Figure 13(d)).…”

Section: B Stepped-temperature Testsmentioning

confidence: 99%

On the Rapid Assessment of Mechanical Behavior of a Prototype Nickel-Based Superalloy using Small-Scale Testing

Sulzer

Alabort

Németh

et al. 2018

Metall Mater Trans A

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An electro-thermal mechanical testing (ETMT) system is used to assess the mechanical behavior of a prototype single-crystal superalloy suitable for industrial gas turbine applications. Miniaturized testpieces of a few mm 2 cross section are used, allowing relatively small volumes to be tested. Novel methods involving temperature ramping and stress relaxation are employed, with the quantitative data measured and then compared to conventional methods. Advantages and limitations of the ETMT system are identified; particularly for the rapid assessment of prototype alloys prior to scale-up to pilot-scale quantities, it is concluded that some significant benefits emerge.

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Diffusion processes during creep at intermediate temperatures in a Ni-based superalloy

Cited by 97 publications

References 29 publications

Segregation-Assisted Plasticity in Ni-Based Superalloys

Segregation-Assisted Plasticity in Ni-Based Superalloys

Influence of composition and precipitation evolution on damage at grain boundaries in a crept polycrystalline Ni-based superalloy

On the Rapid Assessment of Mechanical Behavior of a Prototype Nickel-Based Superalloy using Small-Scale Testing

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