A Study of the Effects of Alloying Additions on TCP Phase Formation in 4&lt;sup&gt;th&lt;/sup&gt; Generation Nickel-Base Single-Crystal Superalloys

Pang, H.T.; Hobbs, R.A.; Stone, H.J.; Rae, C.M.F.

doi:10.4028/www.scientific.net/amr.278.54

Cited by 11 publications

(1 citation statement)

References 7 publications

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“…It is striking that the effect of Mo on the formation of the TCPs in the SRZ is the opposite of that in the substrate [12], This is evident from the earliest observations immediately following the initial 1h anneal after aluminisation. At this point the TCP precipitation in the substrate is limited with LDSX-3 showing some occasional large planar ⌠ TCPs.…”

Section: Discussionmentioning

confidence: 95%

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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Section: Discussionmentioning

confidence: 95%

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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On the Evolution of the γ/γ′ Lattice Misfit and TCP Phase Precipitation in a Highly Alloyed Single Crystalline Ni-Base Superalloy

Bandorf,

Kirzinger,

Zenk

et al. 2024

The Minerals, Metals &Amp; Materials Series

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In Situ Investigation of TCP Phase Formation, Stress Relaxation and γ/γ′ Lattice Misfit Evolution in Fourth Generation Single Crystal Ni-Base Superalloys by X-Ray High Temperature Diffraction

Bezold

Stone

Rae

et al. 2022

Metall Mater Trans A

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In nickel-based superalloys, the lattice misfit between the γ and γ′ phases and the propensity to TCP phase formation at service temperatures critically influence the microstructural evolution that takes place and hence the resultant mechanical properties. In this work, the lattice misfits of a series of highly alloyed Ru-containing 4th generation Ni-base superalloys are investigated by in situ X-ray diffraction (XRD) at high temperature. While the lattice misfit values of all alloys range between − 0.3 and − 1.3 pct at room temperature, they show an atypical temperature dependence, becoming less negative above 900 °C. In situ XRD measurements at 1100 °C reveal that the majority of the internal coherency stresses are already relieved after two hours. This is particularly pronounced for the alloys that have both a lattice misfit larger than |0.6| pct at 1100 °C and are prone to TCP phase formation. However, throughout the relaxation of the internal coherency stresses the lattice misfit remains fairly constant. Due to the similar chemical compositions of the alloys studied, qualitative guidelines for an optimum lattice misfit magnitude are developed by comparing the lattice misfit values with previous creep experiments. Our results indicate that no universal optimal lattice misfit value exists for these alloys and the value strongly depends on the applied creep conditions. Graphical Abstract

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A Study of the Effects of Alloying Additions on TCP Phase Formation in 4<sup>th</sup> Generation Nickel-Base Single-Crystal Superalloys

Cited by 11 publications

References 7 publications

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

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

On the Evolution of the γ/γ′ Lattice Misfit and TCP Phase Precipitation in a Highly Alloyed Single Crystalline Ni-Base Superalloy

In Situ Investigation of TCP Phase Formation, Stress Relaxation and γ/γ′ Lattice Misfit Evolution in Fourth Generation Single Crystal Ni-Base Superalloys by X-Ray High Temperature Diffraction

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