Phase field modeling of channel dislocation activity and γ′ rafting in single crystal Ni–Al

Zhou, Ning; Chen, Shen; Mills, Michael J.; Wang, Y.

doi:10.1016/j.actamat.2007.06.002

Cited by 97 publications

(55 citation statements)

References 33 publications

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“…The Phase Field Model has proved a powerful tool for studying the deformation mechanisms in L1 2 ordered superalloys on the scale of the dislocation interactions with precipitates [1,2]. The method has also been successfully applied to modelling γ' precipitate shearing by dislocations on the {111} plane [3] in single crystal superalloys and to study the role of channel plasticity during rafting [4,5] at higher temperatures and lower stresses (> 1000°C and < 200 MPa). However, the model, described in [3], had limited applicability to simulating γ' cutting at elevated temperatures, because it did not incorporate the formation of extrinsic stacking faults.…”

Section: Introductionmentioning

confidence: 99%

Prediction of Mechanical Behaviour in Ni-Base Superalloys Using the Phase Field Model of Dislocations

Vorontsov

Воскобойников

Rae

2011

AMR

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Abstract. The "Phase-Field Model of Dislocations" (PFMD) was used to simulate shearing of gamma-prime precipitate arrays in single crystal turbine blade superalloys. The focus of the work has been on the cutting of the L1 2 ordered precipitates by a<112>{111} dislocation ribbons during Primary Creep. The Phase Field Model presented incorporates specially developed Generalised Stacking Fault Energy (γ-surface) data obtained from atomistic simulations. The topography of this surface determines the shearing mechanisms observed in the model. The merit of the new γ-surface, is that it accounts for the formation of extrinsic stacking faults, making the model more relevant to creep deformation of superalloys at elevated temperatures.

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Section: Introductionmentioning

confidence: 99%

Prediction of Mechanical Behaviour in Ni-Base Superalloys Using the Phase Field Model of Dislocations

Vorontsov

Воскобойников

Rae

2011

AMR

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“…The associated strain field has been exploited by metallurgists to attain strength improvements [8]. However, excessive strains destabilise the microstructure by promoting directional coarsening (rafting) at elevated temperatures [9,10]. Furthermore, addition of certain refractory elements to increase the lattice misfit favours the formation of brittle topologically close packed phases that denude the microstructure of strengthening γ precipitates [11].…”

Section: Introductionmentioning

confidence: 99%

Coarsening behaviour and interfacial structure of γ′ precipitates in Co-Al-W based superalloys

Vorontsov¹,

Barnard

Rahman³

et al. 2016

Acta Materialia

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This work discusses the effects of alloying on the coarsening behaviour of the L1 2 ordered γ phase and the structure of the γ/γ interfaces in three Co-Al-W base superalloys aged at ∼90 • C below the respective solvus temperatures: Co-7Al-7W, Co10Al-5W-2Ta and Co-7Al-7W-20Ni (at.%). The coarsening kinetics are adequately characterised by the classical Lifshitz-Slyozov-Wagner model for Ostwald ripening. Co-7Al-7W exhibited much slower coarsening than its quaternary derivatives. Alloying can be exploited to modify the coarsening kinetics either by increasing the solvus temperature by adding tantalum, or by adding nickel to shift the rate controlling mechanism towards dependence on the diffusion of aluminium rather than tungsten. Lattice resolution STEM imaging was used to measure the widths of the order-disorder (structural) and Z-contrast (compositional) gradients across the γ/γ interfaces. Similarly to nickel base superalloys, the compositional gradient was found to be wider than the structural. Co-7Al-7W-20Ni had much wider interface gradients than Co-7Al-7W and Co-10Al-5W-2Ta, which suggests that its γ phase stoichiometry is less constrained. A possible correlation between temperature and misfit normalised r vs. t 1 3 coarsening rate coefficients and the structural gradient width has also been identified, whereby alloys with wider interfaces exhibit faster coarsening rates.

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“…Through phase field simulations [16,21,22] we show that this model not only reproduces the crossover from martensite to strain glass at x > x c , but also captures all the important features of the generic phase diagram [see Fig. 1(b)], such as the relatively low crossover PRL 105, 205702 (2010) …”

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confidence: 99%

Modeling Abnormal Strain States in Ferroelastic Systems: The Role of Point Defects

et al. 2010

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Recent experiments have revealed a rich variety of strain states in doped ferroelastic systems. We study the origin of two abnormal strain states; precursory tweed and strain glass, and their relationship with the well-known austenite and martensite (the para-and ferroelastic states). A Landau free energy model is proposed, which assumes that point defects alter the global thermodynamic stability of martensite and create local lattice distortions that interact with the strain order parameters and break the symmetry of the Landau potential. Phase field simulations based on the model have predicted all the important signatures of a strain glass found in experiment. Moreover, the generic ''phase diagram'' constructed from the simulation results shows clearly the relationships among all the strain states, which agrees well with experimental measurements. DOI: 10.1103/PhysRevLett.105.205702 PACS numbers: 64.70.KÀ, 62.20.DÀ, 64.70.PÀ, 81.30.Kf Ferroelastic materials, are generally characterized by two distinct strain states, a strain-disordered paraelastic state (known as the parent phase or austenite) at high temperature and a long-range strain-ordered ferroelastic state (known as martensite) at low temperature. Point defects have been known to play a central role in altering and controlling the properties of ferroelastic materials [1]. In addition to the well-known paraelastic and ferroelastic strain states, it was found that point defects can generate two abnormal strain states: a ''precursory strain state'' (or tweed) characterized by a cross-hatched nanosized strain domain structure [2,3] imbedded in a dynamically disordered paraelastic matrix [4] and a new strain-glass state that is a frozen state of local strain order [5][6][7][8], a ferroelastic analogue to ferroelectric relaxors [9] and cluster spin glasses [10,11].Recent experimental studies have yielded strikingly similar ''phase diagrams'' of strain states for many different doped ferroelastic systems [12][13][14]. An example is given in Fig. 1(a) for a Fe-doped TiNi system [12]. It describes clearly the relationships among all the strain states in ferroelastic systems and shows the following generic features: (i) at a critical doping level x c there exists a rather abrupt crossover from a normal martensitic transition (MT) (x < x c ) to a strain-glass transition (SGT) (x > x c ); (ii) a precursory strain state appears below a temperature T nd , which is well above the M s (MT start temperature) or T g (SGT temperature); (iii) both M s and T g decrease with increasing defect content while T nd decreases at low defect content but increases at high defect content. This generic phase diagram could serve as an experimental validation of any theory proposed to explain the relationship among different strain states in ferroelastic systems.The nature of the precursory strain state (tweed) has been an interesting topic for decades, because it is neither a fully disordered strain state like an ideal austenite nor a fully ordered strain state like the poly-twinn...

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Phase field modeling of channel dislocation activity and γ′ rafting in single crystal Ni–Al

Cited by 97 publications

References 33 publications

Prediction of Mechanical Behaviour in Ni-Base Superalloys Using the Phase Field Model of Dislocations

Prediction of Mechanical Behaviour in Ni-Base Superalloys Using the Phase Field Model of Dislocations

Coarsening behaviour and interfacial structure of γ′ precipitates in Co-Al-W based superalloys

Modeling Abnormal Strain States in Ferroelastic Systems: The Role of Point Defects

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