Mechanisms of Topologically Close-Packed Phase Suppression in an Experimental Ruthenium-Bearing Single-Crystal Nickel-Base Superalloy at 1100 °C

Hobbs, R.A.; Zhang, L.; Rae, C.M.F.; Tin, Sammy

doi:10.1007/s11661-008-9490-9

Cited by 113 publications

(75 citation statements)

References 26 publications

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“…This result and the fact that Mo, Ta and Ti also change the γ/γ'-partitioning ratio, explain the large variety of results in literature which were obtained for very different alloys. [7] discusses possible reasons for the impact of Ru on the nucleation rate of the TCP-phase precipitation. Ru might influence the γ'-phase fraction, the γ/γ'-partitioning ("reverse partitioning") and the interface energy between matrix and precipitate.…”

Section: Discussionmentioning

confidence: 99%

“…Additionally, it is still under dispute whether Ru really influences the γ'-phase fraction or the γ/γ'-partitioning ratio. For example, [7] found a reduction of the γ'-phase fraction by Ru, while [5,25] could not find any in other alloys. It was shown in the previous section that the "reverse partitioning" effect is alloy dependent and this probably also holds for the γ'-phase 184 Euro Superalloys 2010 fraction.…”

Section: Discussionmentioning

confidence: 99%

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Modeling of Precipitation Kinetics of TCP-Phases in Single Crystal Nickel-Base Superalloys

Rettig

Heckl

Singer

2011

AMR

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Abstract. The precipitation of brittle so-called TCP-phases is critical for the application of Recontaining single crystal superalloys. In this work a fully multicomponent precipitation model is presented, which is capable of simulating the precipitation process of the TCP-phases in superalloys considering complex precipitation sequences with several metastable phases. The model is coupled to multicomponent thermodynamic CALPHAD calculations and relies on multicomponent diffusion models based on the TC-API interface of the software DICTRA. The required mobility database has been newly developed and covers all relevant alloying elements of the Ni-base superalloys including rhenium (Re) and ruthenium (Ru). It is well known that adding Ru strongly reduces TCP-phase precipitation. Based on the developed precipitation model, possible mechanisms are investigated to explain this effect and it is concluded that Ru mostly influences the nucleation rate by a combined influence on interface energy, "reverse partitioning" and γ'-phase fraction. IntroductionNickel-base superalloys are widely applied for high temperature applications, especially for turbine blades in the hottest sections of industrial and aero-engine gas turbines [1-2]. Reduction of fuel consumption and engine emissions are very important design goals today. The efficiency of the gas turbine is determined by the burning temperature. Obviously, the material capability of the turbine blades limits this temperature. Therefore improvements in creep strength through material development as well as single-crystalline casting and application of thermal barrier coatings increase the turbine efficiency [3]. Nickel-base superalloys contain typically more than eight alloying elements. Although they have been under investigation for decades due to the complexity there is still space for improvements [2,4]. In the last decade, major improvements in creep strength could be achieved by the development of the 3 rd and 4 th generation single crystalline superalloys, which contain up to 6 wt-% Re and 6 wt-% Ru [1]. Rhenium is known to be a very good solid solution hardener [5], nevertheless it strongly increases the susceptibility to brittle topologically-close packed (TCP) phase precipitation, which limits the acceptable content of rhenium [6][7]. One answer to this problem was to add ruthenium in the 4 th generation superalloys. This element very effectively reduces the TCP-phase precipitation and increases the creep strength [8][9]. The mechanism of this effect is still not well understood [5,7,8,10]. Both elements, Re as well as Ru are extremely expensive and there are doubts on the availability [11]. In order to optimize the alloy composition, the mechanism of the Ru-effect is investigated in this work with numerical methods. Modeling precipitation in superalloys is challenging because of the high number of alloying elements. Most of the multicomponent models developed in the past were applied to high temperature steels. The first, still simple models benefiting from the ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Modeling of Precipitation Kinetics of TCP-Phases in Single Crystal Nickel-Base Superalloys

Rettig

Heckl

Singer

2011

AMR

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“…The latest fourth generation Ni-base superalloys, contain between 2 and 5% Ruthenium (Ru), which improves the mechanical properties in part by suppressing the formation of deleterious intermetallic Topologically Close Packed (TCP) phases [1,2]. This comes at the cost of the degradation of the oxidation resistance and coatings, such as Platinum Aluminide coatings (PtAl) and MCrAlY, are necessary to protect the turbine blades during service, details of these coatings are given elsewhere [3][4][5].…”

Section: Introductionmentioning

confidence: 99%

Secondary Reaction Zone Formations in Pt-Aluminised Fourth Generation Ni-Base Single Crystal Superalloys

Suzuki

Rae

Hobbs

et al. 2011

AMR

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Abstract. Fourth generation superalloys are characterised by the addition of Ru which contributes to improved creep resistance whilst improving the microstructural stability. However, Ru additions have a negative effect on coated Ni-base superalloys, promoting Secondary Reaction Zone (SRZ) formation. Formation of a layer of SRZ beneath an aluminised or Pt-aluminised coating has the potential to reduce the effective cross section of a blade by in excess of 100 µm or 10% of the wall thickness. In this paper the effects of alloy composition on the formation of the SRZ in PtAluminised fourth generation alloys were investigated systematically. A series of experimental fourth generation alloys was used having two distinct compositions of Co, Mo, W and Ru and conforming to a four factorial 'Design of Experiments' model. These alloys showed significant and consistent changes in the SRZ depending on alloy composition. These were in distinct contrast to the effects of these elements on stability in the bulk. Mo was demonstrated to be by far the most effective element suppressing SRZ formation, followed by Co. In contrast, both W and Ru enhance SRZ formation. IntroductionThe latest fourth generation Ni-base superalloys, contain between 2 and 5% Ruthenium (Ru), which improves the mechanical properties in part by suppressing the formation of deleterious intermetallic Topologically Close Packed (TCP) phases [1,2]. This comes at the cost of the degradation of the oxidation resistance and coatings, such as Platinum Aluminide coatings (PtAl) and MCrAlY, are necessary to protect the turbine blades during service, details of these coatings are given elsewhere [3][4][5].The formation of the secondary reaction zone (SRZ) [6-8] is a major problem associated with coated Ni-base superalloys leading to the loss of the coating, and degradation of the properties of coated Ni-base superalloys, and is potentially life-limiting to turbine blades. The SRZ is an intermediate layer formed between an aluminised or Pt-Aluminised coating and the substrate by a discontinuous precipitation reaction similar to recrystallisation. It transforms the metastable aluminium-enriched substrate microstructure into an equilibrium mix of ',  and TCPs. The TCPs coarsen and align perpendicular to the growth direction facilitated by the rapid diffusion path of the high angle boundary. Therefore, the SRZ is associated with poor mechanical properties and provides boundaries allowing a high diffusivity path into the substrate facilitating oxidation and spallation. Traditionally alloys have been developed principally for mechanical performance and any deficit in environmental performance has been remedied by the application of a coating. However the realisation that the longevity and properties of coated Ni-base superalloys are significantly correlated with alloy composition has placed optimisation of the coating performance as a critical part of alloy development. Understanding how the individual alloy elements affect SRZ morphologies in coated fourth generation Ni...

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“…Besides the positive effects of Re on the deformation rate, it has been frequently reported that Re strongly decreases the alloy stability and promotes precipitation of brittle topologically close packed (TCP) phases [3][4][5][6][7][8]. TCP precipitation is highly undesirable and eventually limits the amount of Re that can be added to advantage: On the one hand Re, which preferentially enters the TCP-phases, is removed from the matrix [9,10] lowering the solution strengthening effect, while on the other hand the brittle and needle-like precipitates may grow to considerable size where they act as crack initiation sites [6,7,10].…”

Section: Introductionmentioning

confidence: 99%

“…The detailed mechanisms of the Ru-effect are still under dispute [9,11,[15][16][17][18][19], because the experimental investigation of the retarded precipitation process is difficult and the alloy system is very complex. In the following, numerical simulation will be employed to shed some light on the Ru effect.…”

Section: Introductionmentioning

confidence: 99%

Influence of Ruthenium on Topologically Close Packed Phase Precipitation in Single-crystal Ni-based Superalloys: Numerical Experiments and Validation

Rettig¹,

Singer²

2012

Superalloys 2012 (Twelfth International Symposium)

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The suppression of topologically close-packed phases (TCP) in nickel-based single-crystal superalloys by the addition of ruthenium is modeled with a fully multicomponent mesoscale precipitation model based on the numerical Kampmann-Wagnermethod using thermodynamic CALPHAD-calculations. For the application of the model in ruthenium-containing superalloys, mobility assessments of the binary systems nickel-ruthenium (NiRu) and nickel-rhenium (Ni-Re) were performed to create a new mobility database. It is postulated that the dominating effect of ruthenium regarding more sluggish TCP-phase precipitation is a change of interface energy reducing the number of precipitates nucleating. The precipitation sequences occurring during TCPphase precipitation can be explained using CALPHAD thermodynamics.

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Mechanisms of Topologically Close-Packed Phase Suppression in an Experimental Ruthenium-Bearing Single-Crystal Nickel-Base Superalloy at 1100 °C

Cited by 113 publications

References 26 publications

Modeling of Precipitation Kinetics of TCP-Phases in Single Crystal Nickel-Base Superalloys

Modeling of Precipitation Kinetics of TCP-Phases in Single Crystal Nickel-Base Superalloys

Secondary Reaction Zone Formations in Pt-Aluminised Fourth Generation Ni-Base Single Crystal Superalloys

Influence of Ruthenium on Topologically Close Packed Phase Precipitation in Single-crystal Ni-based Superalloys: Numerical Experiments and Validation

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