Partitioning of Re between γ and γ′ phase in nickel-base superalloys

Volek, Andreas; Pyczak, Florian; Singer, Robert F.; Mughrabi, H.

doi:10.1016/j.scriptamat.2004.09.013

Cited by 128 publications

(65 citation statements)

References 14 publications

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“…3 are seen to strongly partition to the γ ′ phase and γ phase, respectively, which is in good agreement with previous results 10,11,29) . It should be emphasized that the maps of aluminium and rhenium are not continuous across the boundary of the matrix and the intermediate layer, as shown in Fig.…”

Section: Resultssupporting

confidence: 92%

“…Rhenium can increase the solidus and liquidus temperature of the nickel matrix and the volume fraction of γ ′ phase, and is primarily chosen as it is more effective than tantalum and tungsten in this role due to its low solubility in the γ ′ phase 3,[6][7][8] . However, there is an upper limit for the alloying content of Re as high amounts of rhenium degrade the creep and rupture properties due to the formation of topological close packed (TCP) phases induced by the low diffusivity of rhenium in the Ni matrix 9,10) . Single crystal turbine blades are made through the directional solidi cation of investment castings which has been developed to avoid the introduction of casting defects 11) .…”

Section: Introductionmentioning

confidence: 99%

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Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Kim

Withey

2016

Mater. Trans.

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Ni-base single crystal superalloy turbine blades containing defect grains were investigated by high resolution electron microscopy. Several different types of defects, such as, stray grains, equiax grains and freckle chains which formed during casting, and recrystallized grains which formed during subsequent heat treatment, were selected. Regardless of the region of the turbine blade, many particles with large amounts of rhenium were detected at the boundary of the stray grain and matrix. The Re-rich particles were also detected at the boundary of the matrix and other defect grains, such as, equiax grains and freckle chain grains, and even at a low angle grain boundary. However, the boundary of the recrystallised grain and matrix which was formed after solution heat treatment showed just one Re-rich particle. Also, the composition of these Re-rich particles is different from any topologically close packed phases which have been reported in Ni-base superalloys. The results suggest that during solidi cation, the particles are formed from the melt and pushed ahead of each solidi cation front of the defect grain and the matrix, and piled up at the boundary of the matrix/defect grain.

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Section: Resultssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Kim

Withey

2016

Mater. Trans.

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“…Beside the improved tertiary creep lives of Recontaining alloys, Re additions have been observed to considerably reduce the coarsening kinetics of γ precipitates [7], primarily due to the fact that Re strongly favours partitioning to the γ phase. The strong partitioning of Re to the γ phase has been observed in most single-crystal Ni-based superalloys with high γ volume content [4,[8][9][10], and it is supported by first-principles calculations showing Re substitutional defects are unstable in the γ phase [11]. As the γ precipitates coarsen, Re has to diffuse ahead of the γ /γ interface [7].…”

Section: The Rhenium-effectmentioning

confidence: 67%

What is the role of rhenium in single crystal superalloys?

Mottura

Reed

2014

MATEC Web of Conferences

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Abstract. Rhenium plays a critical role in single-crystal superalloys -its addition to first generation alloys improves creep life by a factor of at least two, with further benefits for fatigue performance. Its use in alloys such as PWA1484, CMSX-4 and Rene N5 is now widespread, and many in this community regard Re as the "magic dust". In this paper, the latest thinking concerning the origins of the "rhenium-effect" is presented. We start by reviewing the hypothesis that rhenium clusters represent barriers to dislocation motion. Recent atom probe tomography experiments have shown that Re may instead form a solid solution with Ni at low concentrations (< 7 at.%). Density functional theory calculations indicate that, in the solid solution, short range ordering of Re may be expected. Finally, Re has been shown to diffuse slowly in the γ -Ni phase. Calculations using a semi-analytical dislocation climb/glide model based upon the work of McLean and Dyson have been used to rationalise the composition-dependence of creep deformation in these materials. All evidence points to two important factors: (i) the preferred partitioning of Re to the γ phase, where dislocation activity preferentially occurs during the tertiary creep regime and (ii) a retardation effect on dislocation segments at γ /γ interfaces, which require non-conservative climb and thus an associated vacancy flux.

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“…It has been controversially debated for a long time, whether this effect is responsible for the TCP-phase fraction reduction in 4 th generation superalloys. Nevertheless beside many works claiming the existence of this effect (for example [8,23]), it could not be found in many other alloys (for example [10]). In the following a thermodynamic study with ThermoCalc is presented, which investigates the combined influence of Ru and other alloying element on the partitioning coefficient of Re (see Fig.…”

Section: Resultsmentioning

confidence: 84%

“…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].…”

mentioning

confidence: 99%

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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Partitioning of Re between γ and γ′ phase in nickel-base superalloys

Cited by 128 publications

References 14 publications

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

Detection of Rhenium-Rich Particles at Grain Boundaries in Nickel-Base Superalloy Turbine Blades

What is the role of rhenium in single crystal superalloys?

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

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